WO2014197617A1

WO2014197617A1 - Compositions of resin-linear organosiloxane block copolymers

Info

Publication number: WO2014197617A1
Application number: PCT/US2014/040939
Authority: WO
Inventors: Steven Swier
Original assignee: Dow Corning Corporation
Priority date: 2013-06-05
Filing date: 2014-06-04
Publication date: 2014-12-11

Abstract

Curable compositions of organopolysiloxanes comprising an alkaline earth metal salt and a condensation catalyst are disclosed. The addition of the alkaline earth metal salt to such compositions results in curable compositions and/or cured compositions having at least improved thermal stability over similar compositions lacking the alkaline earth metal salt.

Description

COMPOSITIONS OF

RESIN-LINEAR ORGANOSILOXANE BLOCK COPOLYMERS

CLAIM OF PRIORITY

[0001 ] This application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 61 /831 ,325, filed June 5, 201 3, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUN D

[0002] Light emitting diodes (LEDs) and solar panels use an encapsulant coating to protect electronic components from environmental factors. Such protective coatings must be optically clear to ensure maxi mum efficiency of these devices.

Furthermore, these protective coatings must be tough, durable, long lasting, and yet easy to apply. Many of the currently available coatings, however, lack toughness; are not durable; are not long-lasting; and/or are not easy to apply. There is therefore a continuing need to identify protective and/or functional coatings in many areas of emerging technologies.

BRI EF SUMMARY OF TH E EMBODI MENTS

[0003] Embodiment 1 relates to a curable composition comprising :

i) an organosiloxane block copolymer comprising:

40 to 90 mole percent disiloxy units of the formula [R¹2S1O2/2],

1 0 to 60 mole percent trisiloxy units of the formula [R²Si03/2],

0.5 to 35 mole percent silanol groups [≡SiOH];

wherein :

each R¹ , at each occurrence, is independently a C-| to C30 hydrocarbyl,

each R², at each occurrence, is independently a C-| to C30 hydrocarbyl;

wherein :

the disiloxy units [R¹ 2S1O2/2] are arranged in linear blocks having an average of from 10 to 400 disiloxy units [R¹2Si02/2] per linear block,

the trisiloxy units [R²Si03/2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole, and at least 30% of the non-linear blocks are crosslinked with each other, each linear block is linked to at least one non-linear block; and the organosiloxane block copolymer has a weight average molecular weight (M_w) of at least 20,000 g/mole; and/or

ii) an organopolysiloxane comprising unit formula:

[R¹3Si0₁/2]c[R¹2Si02 2]d[R¹ Si03/2]e[Si0₄ 2]f

wherein each R¹ is, as defined herein, and is independently a C-| to C30 hydrocarbyl; the organopolysiloxane comprises from 1 to about 80 mole % silanol groups [≡SiOH], and the subscripts c, d, e, and f represent the mole fraction of each siloxy unit present in the organopolysiloxane and range as follows: c is about 0 to about 0.6, d is about 0 to about 1 , e is about 0 to about 1 , f is about 0 to about 0.6, with the provisos that d+e+f > 0, c+d+e+f < 1 ;

ii) an alkaline earth metal salt; and

iii) a condensation catalyst.

[0004] Embodiment 2 relates to the curable composition of Embodiment 1 , further comprising a solvent, a filler or a phosphor.

[0005] Embodiment 3 relates to the curable composition of Embodiment 1 or 2, wherein the condensation catalyst comprises a metal ligand complex.

[0006] Embodiment 4 relates to the curable composition of Embodiment 3, wherein the metal ligand complex comprises a metal acetylacetonate complex.

[0007] Embodiment 5 relates to the curable composition of Embodiment 3 or 4, wherein the metal is Al, Bi, Sn, Ti or Zr.

[0008] Embodiment 6 relates to the curable composition of Embodiment 5, wherein the metal ligand complex comprises aluminum trisacetylacetonate.

[0009] Embodiment 7 relates to the curable composition of Embodiment 1 or 2, wherein the condensation catalyst comprises a basic compound.

[0010] Embodiment 8 relates to the curable composition of Embodiment 7, wherein the basic compound comprises diazabicycloundecene (DBU).

[0011 ] Embodiment 9 relates to the curable composition of Embodiments 1 -8, wherein is phenyl.

[0012] Embodiment 10 relates to the curable composition of Embodiments 1 -9, wherein R¹ is methyl or phenyl.

[0013] Embodiment 1 1 relates to the curable composition of Embodiments 1 -10, wherein the disiloxy units have the formula [(CH3)(C6H5)Si02/2]- [0014] Embodiment 12 relates to the curable composition of Embodiments 1 -1 1 , wherein the disiloxy units have the formula [(CH3)2Si02/2_.- [0015] Embodiment 13 relates to the curable composition of Embodiments 1 -12, wherein the alkaline earth metal salt comprises an alkaline earth metal salt of the formula MX^"! 2, and hydrates or solvates thereof, wherein M represents an alkaline earth metal and X¹ represents any suitable counterion.

[0016] Embodiment 14 relates to the curable composition of Embodiments 1 -13, wherein the alkaline earth metal salt comprises an alkaline earth metal hydroxide or an alkaline earth metal hydroxide hydrate of the formula (OH)2-p H2O wherein M represents an alkaline earth metal and p ranges from 0 to 8.

[0017] Embodiment 1 5 relates to the curable composition of Embodiment 1 3 or 14, wherein M is barium.

[0018] Embodiment 1 6 relates to the curable composition of Embodiments 1 -15, wherein the alkaline earth metal salt is present in an amount sufficient to improve the thermal stability of the curable composition.

[0019] Embodiment 17 relates to the curable composition of Embodiment 1 6, wherein the amount of alkaline earth metal salt sufficient to improve thermal stability of the curable composition, in terms of alkaline earth metal level as a function of solids, is from about 25 ppm to about 10,000 ppm.

[0020] Embodiment 18 relates to the curable composition of Embodiment 1 -17, wherein 0.2 < c+d+e+f ≤ 1 .

[0021 ] Embodiment 19 relates to the curable composition of Embodiment 1 -18, wherein the condensation catalyst comprises a metal ligand complex and the molar ratio of the metal in the metal-ligand complex to the alkaline earth metal is from about 1 :4 to about 3:4.

[0022] Embodiment 20 relates to a solid film composition comprising the curable composition of Embodiments 1 -19.

[0023] Embodiment 21 relates to the solid film composition of Embodiment 20, wherein the solid composition has an optical transmittance of at least 95%.

[0024] Embodiment 22 relates to the cured product of the composition of Embodiments 1 -21 .

[0025] Embodiment 23 relates to the cured product of Embodiment 22, wherein the alkaline earth metal salt is present in an amount sufficient to improve the thermal stability of the cured product. [0026] Embodiment 24 relates to an LED encapsulant comprising the compositions of Embodiments 1 -23.

[0027] Embodiment 25 relates to a method for increasing the thermal stability of a curable composition comprising:

i) a condensation catalyst; and

ii) an organosiloxane block copolymer comprising:

40 to 90 mole percent disiloxy units of the formula [R¹2S1O2/2],

1 0 to 60 mole percent trisiloxy units of the formula [R²SiC>3/2],

0.5 to 35 mole percent silanol groups [≡SiOH];

wherein :

each R¹ , at each occurrence, is independently a C-| to C30 hydrocarbyl,

each R², at each occurrence, is independently a C-| to C30 hydrocarbyl;

wherein :

the trisiloxy units [R²SiC>3/2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole, and at least 30% of the non-linear blocks are crosslinked with each other, each linear block is linked to at least one non-linear block; and

the organosiloxane block copolymer has a weight average molecular weight (M_w) of at least 20,000 g/mole; and/or

an organopolysiloxane comprising unit formula:

[R¹ 3Si0₁/2]c[R¹2Si02 2]d[R¹ Si03/2]e[Si0₄ 2]f

the method comprising contacting the curable composition with an alkaline earth metal salt. [0028] Embodiment 26 relates to the method of Embodiment 25, wherein the increase in thermal stability comprises a reduction in the production of benzene upon curing and/or heat aging the curable composition.

[0029] Embodiment 27 relates to the method of Embodiment 25, wherein the alkaline earth metal salt is present in an amount sufficient to improve the thermal stability of the curable composition.

DETAILED DESCRI PTION OF THE EMBODIMENTS

[0030] The present disclosure provides curable and solid compositions comprising organopolysiloxanes, including "resin linear" organosiloxane block copolymers, where the compositions comprise an alkaline earth metal salt and a condensation catalyst {e.g., a metal ligand complex or a basic compound, such as DBU). The alkaline earth metal salt is present in an amount sufficient to, among other things, protect the curable and solid compositions from any adverse effects the catalyst may have on the thermal stability of the organopolysiloxanes, including "resin linear" organosiloxane block copolymers, before, during or after cure.

[0031 ] In some embodiments, the curable compositions described herein comprise:

i) an organosiloxane block copolymer comprising:

40 to 90 mole percent disiloxy units of the formula [R¹2Si02/2L

10 to 60 mole percent trisiloxy units of the formula [R²Si03/2],

0.5 to 35 mole percent silanol groups [≡SiOH];

wherein:

each R¹ , at each occurrence, is independently a C-_| to C30 hydrocarbyl,

each R², at each occurrence, is independently a C-| to C30 hydrocarbyl,

wherein:

the disiloxy units [R¹2S1O2/2] are arranged in linear blocks having an average of from 10 to 400 disiloxy units [R¹2Si02/2] per linear block,

the trisiloxy units [R²Si03 2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole, and at least 30% of the non-linear blocks are crosslinked with each other, each linear block is linked to at least one non-linear block, and

the organosiloxane block copolymer has an average molecular weight (M_w) of at least 20,000 g/mole; and/or

(ii) organopolysiloxane comprising unit formula: [R¹3Si0₁/2]c[R¹2Si02 2]d[R¹ Si03/2]e[Si0₄ 2]f wherein each R¹ is, as defined herein, and is independently a C-| to C30 hydrocarbyl; the organopolysiloxane comprises from 1 to about 80 mole % silanol groups [≡SiOH], and the subscripts c, d, e, and f represent the mole fraction of each siloxy unit present in the organopolysiloxane and range as follows: c is about 0 to about 0.6, d is about 0 to about 1 , e is about 0 to about 1 , f is about 0 to about 0.6, with the provisos that d+e+f > 0, c+d+e+f < 1 ;

ii) an alkaline earth metal salt; and

iii) a condensation catalyst.

[0032] The organopolysiloxanes of the embodiments described herein include "resin-linear" organosiloxane block copolymers, as well as "resin'V'resinous" and "linear" organopolysiloxanes {e.g., those comprising unit formula

[R¹3SiOi /2]c[^Rl 2^Si02/2]d[^{Rl si0}3/2]e[^Si04/2]f)- Methods of preparing such organopolysiloxanes and compositions comprising such organopolysiloxanes are known in the art. See, e.g., Published PCT Application Nos. WO2012/040305 and WO2012/040367, the entireties of both of which are incorporated by reference as if fully set forth herein.

[0033] Organopolysiloxanes are polymers containing siloxy units independently selected from [R3S1O-1/2], [R2S1O2/2]. [RS1O3/2], or [S1O4/2] siloxy units, where R may be, e.g., any organic group. These siloxy units are commonly referred to as M, D, T, and Q units respectively. These siloxy units can be combined in various manners to form cyclic, linear, or branched structures. The chemical and physical properties of the resulting polymeric structures vary depending on the number and type of siloxy units in the organopolysiloxane. For example, "linear" organopolysiloxanes contain, in some embodiments, mostly D, or [R2S1O2/2] siloxy units, which results in polydiorganosiloxanes that are fluids of varying viscosities, depending on the "degree of polymerization" or "dp" as indicated by the number of D units in the polydiorganosiloxane. "Linear" organopolysiloxanes, in some embodiments, have glass transition temperatures (Tg) that are lower than 25°C. "Resin" or "resinous" organopolysiloxanes result when a majority of the siloxy units are selected from T or Q siloxy units. When T siloxy units are predominately used to prepare an organopolysiloxane, the resulting organosiloxane is often referred to as a "resin" or a "silsesquioxane resin." Increasing the amount of T or Q siloxy units in an organopolysiloxane, in some embodiments, results in polymers having increasing hardness and/or glass like properties. "Resin" organopolysiloxanes thus have higher Tg values, for example siloxane resins often have Tg values greater than 40°C, e.g., greater than 50°C, greater than 60°C, greater than 70°C, greater than 80°C, greater than 90°C or greater than 100°C. In some embodiments, Tg for siloxane resins is from about 60°C to about 100°C, e.g., from about 60°C to about 80°C, from about 50°C to about 100°C, from about 50°C to about 80°C or from about 70°C to about 100°C.

Oraanosiloxane block copolymers

[0034] As used herein "organosiloxane block copolymers" or "resin-linear organosiloxane block copolymers" refer to organopolysiloxanes containing "linear" D siloxy units in combination with "resin" T siloxy units. In some embodiments, the organosiloxane copolymers are "block" copolymers, as opposed to "random" copolymers. As such, the "resin-linear organosiloxane block copolymers" of the disclosed embodiments refer to organopolysiloxanes containing D and T siloxy units, where the D units (i.e., [R¹2Si02/2] units) are primarily bonded together to form polymeric chains having, in some embodiments, an average of from 10 to 400 D units (e.g., an average of from about 10 to about 350 D units; about 10 to about 300 D units; about 10 to about 200 D units; about 10 to about 100 D units; about 50 to about 400 D units; about 100 to about 400 D units; about 150 to about 400 D units; about 200 to about 400 D units; about 300 to about 400 D units; about 50 to about 300 D units; about 100 to about 300 D units; about 150 to about 300 D units; about 200 to about 300 D units; about 100 to about 150 D units, about 1 15 to about 125 D units, about 90 to about 170 D units or about 1 10 to about 140 D units), which are referred herein as "linear blocks."

[0035] The T units (i.e., [R²SiC>3/2]) are, in some embodiments, primarily bonded to each other to form branched polymeric chains, which are referred to as "non-linear blocks." In some embodiments, a significant number of these non-linear blocks may further aggregate to form "nano-domains" when solid forms of the block copolymer are provided. In some embodiments, these nano-domains form a phase separate from a phase formed from linear blocks having D units, such that a resin-rich phase forms. In some embodiments, the disiloxy units [ ¹ 2SiC>2/2] are arranged in linear blocks having an average of from 1 0 to 400 disiloxy units [R¹2Si02/2] per linear block {e.g., an average of from about 10 to about 350 D units; about 10 to about 300 D units; about 10 to about 200 D units; about 10 to about 1 00 D units; about 50 to about 400 D units; about 100 to about 400 D units; about 150 to about 400 D units; about 200 to about 400 D units; about 300 to about 400 D units; about 50 to about 300 D units; about 100 to about 300 D units; about 150 to about 300 D units; about 200 to about 300 D units; about 100 to about 150 D units, about 1 15 to about 125 D units, about 90 to about 170 D units or about 1 10 to about 140 D units), and the trisiloxy units [R²Si03 2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole and at least 30% of the non-linear blocks are crosslinked with each other.

[0036] In some embodiments, the non-linear blocks have a number average molecular weight of at least 500 g/mole, e.g., at least 1000 g/mole, at least 2000 g/mole, at least 3000 g/mole or at least 4000 g/mole; or have a molecular weight of from about 500 g/mole to about 4000 g/mole, from about 500 g/mole to about 3000 g/mole, from about 500 g/mole to about 2000 g/mole, from about 500 g/mole to about 1000 g/mole, from about 1000 g/mole to 2000 g/mole, from about 1000 g/mole to about 1500 g/mole, from about 1000 g/mole to about 1200 g/mole, from about 1 000 g/mole to 3000 g/mole, from about 1000 g/mole to about 2500 g/mole, from about 1 000 g/mole to about 4000 g/mole, from about 2000 g/mole to about 3000 g/mole or from about 2000 g/mole to about 4000 g/mole.

[0037] In some embodiments, at least 30% of the non-linear blocks are crosslinked with each other, e.g., at least 40% of the non-linear blocks are crosslinked with each other; at least 50% of the non-linear blocks are crosslinked with each other; at least 60% of the non-linear blocks are crosslinked with each other; at least 70% of the non-linear blocks are crosslinked with each other; or at least 80% of the nonlinear blocks are crosslinked with each other, wherein all of the percentages given herein to indicate percent non-linear blocks that are crosslinked are in weight percent. In other embodiments, from about 30% to about 80% of the non-linear blocks are crosslinked with each other; from about 30% to about 70% of the nonlinear blocks are crosslinked with each other; from about 30% to about 60% of the non-linear blocks are crosslinked with each other; from about 30% to about 50% of the non-linear blocks are crosslinked with each other; from about 30% to about 40% of the non-linear blocks are crosslinked with each other; from about 40% to about 80% of the non-linear blocks are crosslinked with each other; from about 40% to about 70% of the non-linear blocks are crosslinked with each other; from about 40% to about 60% of the non-linear blocks are crosslinked with each other; from about 40% to about 50% of the non-linear blocks are crosslinked with each other; from about 50% to about 80% of the non-linear blocks are crosslinked with each other; from about 50% to about 70% of the non-linear blocks are crosslinked with each other; from about 55% to about 70% of the non-linear blocks are crosslinked with each other, from about 50% to about 60% of the non-linear blocks are crosslinked with each other; from about 60% to about 80% of the non-linear blocks are crosslinked with each other; or from about 60% to about 70% of the nonlinear blocks are crosslinked with each other.

[0038] The organosiloxane block copolymers {e.g., those comprising 40 to 90 mole percent disiloxy units of the formula [R¹ 2S1O2/2] and 1 0 to 60 mole percent trisiloxy units of the formula [R²SiC>3/2]) may be represented by the formula

[R¹2Si02/2]a.^R2Si03/2]b where the subscripts a and b represent the mole fractions of the siloxy units in the copolymer,

a is about 0.4 to about 0.9,

alternatively about 0.5 to about 0.9,

alternatively about 0.6 to about 0.9,

b is about 0.1 to 0.6 about,

alternatively about 0.1 to about 0.5,

alternatively about 0.1 to about 0.4,

wherein each R¹ , at each occurrence, is independently a C-| to C30 hydrocarbyl, and each R², at each occurrence, is independently a C-| to C30 hydrocarbyl.

[0039] In some embodiments, the organosiloxane block copolymers of the embodiments described herein comprise 40 to 90 mole percent disiloxy units of the formula [R¹ 2Si02/2]_> ^e-9 _> 50 to 90 mole percent disiloxy units of the formula [R¹2Si02 2] ; 60 to 90 mole percent disiloxy units of the formula [R¹2SiC>2/2] ; 65 to 90 mole percent disiloxy units of the formula [R¹ 2SiC>2/2] ; ⁷^ to 90 mole percent disiloxy units of the formula [R¹2Si02/2]; or 80 to 90 mole percent disiloxy units of the formula [R¹ 2SiC>2/2] ; 40 to 80 mole percent disiloxy units of the formula [R¹2SiO2/2] ; 40 to 70 mole percent disiloxy units of the formula [R¹2SiO2 2] ; 40 to 60 mole percent disiloxy units of the formula [R¹ 2SiO2/2l ; 40 to 50 mole percent disiloxy units of the formula [R¹2SiO2/2.; 50 to 80 mole percent disiloxy units of the formula [R¹2SiO2/2]; 50 to 70 mole percent disiloxy units of the formula [R¹2SiO2/2. ; 50 to 60 mole percent disiloxy units of the formula [R¹2SiO2 2] ; 60 to 80 mole percent disiloxy units of the formula [R¹ 2SiO2 2l ; 60 to 70 mole percent disiloxy units of the formula [R¹2SiO2/2]; or 70 to 80 mole percent disiloxy units of the formula [R¹2SiO2/2.-

[0040] In some embodiments, the organosiloxane block copolymers of the embodiments described herein comprise 10 to 60 mole percent trisiloxy units of the formula [R²SiO3/2], e.g., 10 to 20 mole percent trisiloxy units of the formula [R²SiO3/2]; 10 to 30 mole percent trisiloxy units of the formula [R²SiO3/2]; 1 0 to 35 mole percent trisiloxy units of the formula [R²SiO3 2]; 1 0 to 40 mole percent trisiloxy units of the formula [R²SiO3/2]; 1 0 to 50 mole percent trisiloxy units of the formula [R²SiO3 2] ; 20 to 30 mole percent trisiloxy units of the formula [R²SiO3/2]; 20 to 35 mole percent trisiloxy units of the formula [R²SiO3/2]; 20 to 40 mole percent trisiloxy units of the formula [R²SiO3/2]; 20 to 50 mole percent trisiloxy units of the formula [R²SiO3/2]; 20 to 60 mole percent trisiloxy units of the formula [R²SiO3/2]; 30 to 40 mole percent trisiloxy units of the formula [R²SiO3/2]; 30 to 50 mole percent trisiloxy units of the formula [R²SiO3 2]; 30 to 60 mole percent trisiloxy units of the formula [R²SiO3/2]; 40 to 50 mole percent trisiloxy units of the formula [R²SiO3/2] ; or 40 to 60 mole percent trisiloxy units of the formula [R²SiO_3/2].

[0041 ] It should be understood that the organosiloxane block copolymers of the embodiments described herein may contain additional siloxy units, such as M siloxy units, Q siloxy units, other unique D or T siloxy units (for example, having organic groups other than R¹ or R²), provided that the organosiloxane block copolymer contains the mole fractions of the disiloxy and trisiloxy units as described herein. In other words, the sum of the mole fractions as designated by subscripts a and b, do not necessarily have to sum to one. The sum of a + b may be less than one to account for minor amounts of other siloxy units that may be present in the organosiloxane block copolymer. Alternatively, the sum of a + b is greater than 0.6, alternatively greater than 0.7, alternatively greater than 0.8, or alternatively greater than 0.9. In some embodiments, the sum of a + b is from about 0.6 to about 0.9, e.g., from about 0.6 to about 0.8, from about 0.6 to about 0.7, from about 0.7 to about 0.9, from about 0.7 to about 0.8, or from about 0.8 to about 0.9.

[0042] In one embodiment, the organosiloxane block copolymer consists essentially of the disiloxy units of the formula [R¹2Si02/2] and trisiloxy units of the formula [R²SiC>3/2], while also containing 0.5 to 25 mole percent silanol groups [≡SiOH]

{e.g., 0.5 to 5 mole percent, 0.5 to 1 0 mole percent, 0.5 to 1 5 mole percent, 0.5 to 20 mole percent, 5 to 10 mole percent, 5 to 15 mole percent, 5 to 20 mole percent, 5 to 25 mole percent, 10 to 15 mole percent 10 to 20 mole percent, 10 to 25 mole percent, 15 to 20 mole percent, 1 5 to 25 mole percent, or 20 to 25 mole percent), where R^ and R^ are as defined above. Thus, some embodiments, the sum of a + b (when using mole fractions to represent the amount of disiloxy and trisiloxy units in the copolymer) is greater than 0.95, alternatively greater than 0.98.

[0043] In some embodiments, the resin-linear organosiloxane block copolymers also contain silanol groups (≡SiOH). The amount of silanol groups present on the organosiloxane block copolymer may vary from 0.5 to 35 mole percent silanol groups [≡SiOH],

alternatively from 2 to 32 mole percent silanol groups [≡SiOH],

alternatively from 8 to 22 mole percent silanol groups [≡SiOH].

The silanol groups may be present on any siloxy units within the organosiloxane block copolymer. The amount described herein represent the total amount of silanol groups found in the organosiloxane block copolymer. In some embodiments, the majority {e.g., greater than 75%, greater than 80%, greater than 90%; from about 75% to about 90%, from about 80% to about 90%, or from about 75% to about 85%) of the silanol groups will reside on the trisiloxy units, i.e., the resin component of the block copolymer. Although not wishing to be bound by any theory, the silanol groups present on the resin component of the organosiloxane block copolymer allows for the block copolymer to further react or cure at elevated temperatures.

[0044] At each occurrence, each R¹ in the above disiloxy unit is independently a C-| to C30 hydrocarbyl (e.g., a C-| to C20 hydrocarbyl, a Ci to C-| Q hydrocarbyl or a C-| to CQ hydrocarbyl), where the hydrocarbyl group may independently be an alkyl, aryl, or alkylaryl group. Each R¹ , at each occurrence, may independently be a C-| to C30 alkyl group, alternatively, at each occurrence, each R¹ may be a C-| to C-| 8 alkyl group. Alternatively each R¹ , at each occurrence, may be a C-| to C5 alkyl group such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. Alternatively each R¹ , at each occurrence, may be methyl. Each R¹ , at each occurrence, may be an aryl group, such as phenyl, naphthyl, or an anthryl group. Alternatively, each R¹ , at each occurrence, may be any combination of the aforementioned alkyl or aryl groups such that, in some embodiments, each disiloxy unit may have two alkyl groups {e.g., two methyl groups); two aryl groups {e.g., two phenyl groups); or an alkyl {e.g., methyl) and an aryl group {e.g., phenyl). Alternatively, each R¹ , at each occurrence, is phenyl or methyl.

[0045] Each R², at each occurrence, in the above trisiloxy unit is independently a C-| to C30 hydrocarbyl {e.g., a C-| to C20 hydrocarbyl, a C-| to C-| Q hydrocarbyl or a C-| to CQ hydrocarbyl), where the hydrocarbyl group may independently be an alkyl, aryl, or alkylaryl group. Each R², at each occurrence, may be a C-| to C20 alkyl group, alternatively each R², at each occurrence, may be a C-| to C-| 3 alkyl group.

Alternatively each R², at each occurrence, may be a Ci to CQ alkyl group such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. Alternatively each R², at each occurrence, may be methyl. Each R², at each occurrence, may be an aryl group, such as phenyl, naphthyl, or an anthryl group. Alternatively, each R², at each occurrence, may be any combination of the aforementioned alkyl or aryl groups such that, in some embodiments, each disiloxy unit may have two alkyl groups {e.g., two methyl groups); two aryl groups {e.g., two phenyl groups) ; or an alkyl

{e.g., methyl) and an aryl group {e.g., phenyl). Alternatively, each R², at each occurrence, is phenyl or methyl. [0046] As used throughout the specification, hydrocarbyl also includes substituted hydrocarbyls. "Substituted" as used throughout the specification refers broadly to replacement of one or more of the hydrogen atoms of the group with substituents known to those skilled in the art and resulting in a stable compound as described herein. Examples of suitable substituents include, but are not limited to, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, alkaryl, hydroxy, alkoxy, aryloxy, carboxy (i.e., C0₂H), carboxyalkyl, carboxyaryl, cyano, nitro and the like. Substituted hydrocabyl also includes halogen substituted hydrocarbyls, where the halogen may be fluorine, chlorine, bromine or combinations thereof.

[0047] In some embodiments, fluorinated organosiloxane block copolymers are also contemplated herein. Such fluorinated orangsiloxane block copolymers are described in U.S. Provisional Patent Appl. Ser. No. 61 /608,732, filed March 9, 2012; and PCT Appl. No. PCT/US2013/027904, filed February 27, 2013, the entire disclosures of both of which are incorporated by reference as if fully set forth herein.

[0048] The formula [R¹2Si02/2.a-^R2Si03/2]b> ^ancl related formulae using mole fractions, as used herein to describe the organosiloxane block copolymers, does not indicate structural ordering of the disiloxy [R¹2Si02/2. and trisiloxy [R²SiC>3/2] units in the copolymer. Rather, this formula is meant to provide a convenient notation to describe the relative amounts of the two units in the copolymer, as per the mole fractions described herein via the subscripts a and b. The mole fractions of the various siloxy units in the present organosiloxane block copolymers, as well as the silanol content, may be readily determined by ²⁹Si NMR techniques, as detailed in the Examples.

[0049] The organosiloxane block copolymers of the embodiments described herein have a weight average molecular weight (M_w) of at least 20,000 g/mole, alternatively a weight average molecular weight of at least 40,000 g/mole, alternatively a weight average molecular weight of at least 50,000 g/mole, alternatively a weight average molecular weight of at least 60,000 g/mole, alternatively a weight average molecular weight of at least 70,000 g/mole, or alternatively a weight average molecular weight of at least 80,000 g/mole. In some embodiments, the organosiloxane block copolymers of the embodiments described herein have a weight average molecular weight (M_w) of from about 20,000 g/mole to about 250,000 g/mole or from about 1 00,000 g/mole to about 250,000 g/mole, alternatively a weight average molecular weight of from about 40,000 g/mole to about 100,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 100,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 80,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 70,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 60,000 g/mole. In some embodiments, the organosiloxane block copolymers of the embodiments described herein have a number average molecular weight (M_n) of from about 15,000 to about 50,000 g/mole; from about

15,000 to about 30,000 g/mole; from about 20,000 to about 30,000 g/mole; or from about 20,000 to about 25,000 g/mole. The average molecular weight may be readily determined using Gel Permeation Chromatography (GPC) techniques, such as those described in the Examples.

[0050] In some embodiments, the structural ordering of the disiloxy and trisiloxy units may be further described as follows: the disiloxy units [R¹ 2SiC>2/2] are arranged in linear blocks having an average of from 1 0 to 400 disiloxy units [R¹2Si02/2. P^er linear block, and the trisiloxy units [R²SiC>3/2] are arranged in non^¬ linear blocks having a molecular weight of at least 500 g/mole. Each linear block is linked to at least one non-linear block in the block copolymer. Furthermore, at least 30% of the non-linear blocks are crosslinked with each other,

alternatively at least at 40% of the non-linear blocks are crosslinked with each other,

alternatively at least at 50% of the non-linear blocks are crosslinked with each other.

[0051 ] In other embodiments, from about 30% to about 80% of the non-linear blocks are crosslinked with each other; from about 30% to about 70% of the nonlinear blocks are crosslinked with each other; from about 30% to about 60% of the non-linear blocks are crosslinked with each other; from about 30% to about 50% of the non-linear blocks are crosslinked with each other; from about 30% to about 40% of the non-linear blocks are crosslinked with each other; from about 40% to about 80% of the non-linear blocks are crosslinked with each other; from about 40% to about 70% of the non-linear blocks are crosslinked with each other; from about 40% to about 60% of the non-linear blocks are crosslinked with each other; from about 40% to about 50% of the non-linear blocks are crosslinked with each other; from about 50% to about 80% of the non-linear blocks are crosslinked with each other; from about 50% to about 70% of the non-linear blocks are crosslinked with each other; from about 50% to about 60% of the non-linear blocks are crosslinked with each other; from about 60% to about 80% of the non-linear blocks are crosslinked with each other; or from about 60% to about 70% of the non-linear blocks are crosslinked with each other.

[0052] The crosslinking of the non-linear blocks may be accomplished via a variety of chemical mechanisms and/or moieties. For example, crosslinking of non-linear blocks within the block copolymer may result from the condensation of residual silanol groups present in the non-linear blocks of the copolymer. Crosslinking of the non-linear blocks within the block copolymer may also occur between "free resin" components and the non-linear blocks. "Free resin" components may be present in the block copolymer compositions as a result of using an excess amount of an organosiloxane resin during the preparation of the block copolymer. The free resin component may crosslink with the non-linear blocks by condensation of the residual silanol groups present on the non-blocks and on the free resin. The free resin may provide crosslinking by reacting with lower molecular weight compounds added as crosslinkers, as described herein. The free resin, when present, may be present in an amount of from about 10% to about 20% by weight of the organosiloxane block copolymers of the embodiments described herein, e.g., from about 15% to about 20% by weight organosiloxane block copolymers of the embodiments described herein.

[0053] Alternatively, certain compounds may be added during the preparation of the block copolymer to specifically crosslink the non-resin blocks. These crosslinking compounds may include an organosilane having the formula R⁵qSiX4_q, which is added during the formation of the block copolymer (step II) as discussed herein), where is a C-| to Cs hydrocarbyl or a C-| to Cs halogen-substituted hydrocarbyl ; X is a hydrolyzable group; and q is 0, 1 , or 2. R⁵ is a Ci to CQ hydrocarbyl or a C-| to CQ halogen-substituted hydrocarbyl, or alternatively R⁵ is a C-| to CQ alkyl group, or alternatively a phenyl group, or alternatively R^ is methyl, ethyl, or a combination of methyl and ethyl. X is any hydrolyzable group, alternatively X may be an oximo, acetoxy, halogen atom, hydroxyl (OH), or an alkoxy group.

[0054] In one embodiment, the organosilane having the formula R⁵qSiX4_q is an alkyltriacetoxysilane, such as methyltriacetoxysilane, ethyltriacetoxysilane, or a combination of both. Commercially available representative alkyltriacetoxysilanes include ETS-900 (Dow Corning Corp., Midland, Ml).

[0055] Other suitable, non-limiting organosilanes useful as crosslinkers include; methyl tris(methylethylketoxime)silane (MTO), methyl triacetoxysilane, ethyl triacetoxysilane, tetraacetoxysilane, tetraoximesilane, dimethyl diacetoxysilane, dimethyl dioximesilane, and methyl tris(methylmethylketoxime)silane.

[0056] In some embodiments, the crosslinks within the block copolymer will primarily be siloxane bonds,≡Si-0-Si≡, resulting from the condensation of silanol groups, as discussed herein.

[0057] The amount of crosslinking in the block copolymer may be estimated by determining the average molecular weight of the block copolymer, such as with GPC techniques. In some embodiments, crosslinking the block copolymer increases its average molecular weight. Thus, an estimation of the extent of crosslinking may be made, given the average molecular weight of the block copolymer, the selection of the linear siloxy component (that is the chain length as indicated by its degree of polymerization), and the molecular weight of the nonlinear block (which is primarily controlled by the selection of the selection of the organosiloxane resin used to prepare the block copolymer).

"Resinous" and "Linear" Oraanopolvsiloxanes

[0058] As mentioned previously, the curable compositions described herein may comprise, in addition to or instead of a resin-linear block copolymer, "resin'V'resinous" and/or "linear" organopolysiloxanes comprising unit formula

[R¹3SiOi/2]c[^Rl 2Si02/2]d[^Rl Si03/2]_e[Si04/2]f, wherein R², c, d, e, and f are as defined herein; c+d+e+f < 1 and, in some embodiments, 0.2 < c+d+e+f < 1 . Such organopolysiloxanes comprises from 1 to about 80 mole % silanol groups [≡SiOH] (e.g., from about 1 to about 50 mole % silanol groups, from about 1 to about 25 mole % silanol groups, from about 1 to about 20 mole % silanol groups, from about 1 to about 15 mole% silanol groups or from about 1 to about 10 mole % silanol groups). [0059] The weight average molecular weight (M_w) of the organopolysiloxane resin is not limiting, but, in some embodiments, ranges from 1 ,000 to 10,000, or alternatively 1 ,500 to 5,000 g/mole.

[0060] The above average formula used to refer to "resinous" and "linear" organopolysiloxanes using mole fractions does not indicate structural ordering of the various siloxy units in the copolymer. Rather, this formula is meant to provide a convenient notation to describe the relative amounts of the siloxy units in the copolymer, as per the mole fractions described herein via the subscripts. The mole fractions of the various siloxy units in the present organopolysiloxanes, as well as the silanol content, may be readily determined by ²^Si NMR techniques.

[0061 ] The organopolysiloxanes comprising unit formula

[R¹3SiOi _/2]_C[R¹ 2Si0₂ 2]d[^Rl Si0₃/2]e[Si04 2]f may be "linear" organopolysiloxanes, where a majority {e.g., greater than 60%; greater than 75%, greater than 80%, greater than 90%; from about 75% to about 90%, from about 80% to about 90%, or from about 75% to about 85%) of siloxy units in the organopolysiloxane are R²2Si02/2 units, and/or substantially "resinous" organopolysiloxanes, where the majority {e.g., greater than 60%; greater than 75%, greater than 80%, greater than 90%; from about 75% to about 90%, from about 80% to about 90%, or from about 75% to about 85%) of siloxy units in the organopolysiloxane are R²SiC>3/2 and/or S1O4/2 units.

[0062] In some embodiments, fluorinated analogs of the aforementioned "linear" organopolysiloxanes and/or "resinous" organopolysiloxanes may be used. Examples of such fluorinated analogs include, but are not limited to, those described in U.S. Provisional Patent Appl. Ser. No. 61/608,732, filed March 9, 2012; and PCT Appl. No. PCT/US2013/027904 the entire disclosures of both which are incorporated by reference as if fully set forth herein. Such fluorinated analogs may be used in addition to, or in place of the non-fluorinated analogs of the organopolysiloxanes.

[0063] "Linear" organopolysiloxane organopolysiloxanes comprising unit formula

[R¹3SiOi/2lc[^Rl 2Si02/2]d[^Rl Si03/2]_e[Si04/2]f may be a polydiorganosiloxane. Such polydiorganosiloxanes, in some embodiments, contain a majority of R²2SiC>2/2 siloxy units in their formula (for example, where d would be greater than 0.5 in the above average formula). In some embodiments, the polydiorganosiloxane contains a majority of [(aryl)(alkyl)Si02/2] siloxy units (e.g., [(CgH5)(CH3)Si02/2] siloxy units, such as polymethylphenylsiloxanes). Suitable polydiorganosiloxanes includes those having the average formula:

(CH₃)3SiO[(CH3)₂SiO]_mSi(CH₃)3

(CH₃)3SiO[(C₆H5)(CH3)SiO]_mSi(CH₃)3

(CH₃)(C₆H5)2SiO[(C₆H5)(CH3)SiO]_mSi(C₆H5)2(CH₃) and

(CH₃)2(C₆H5)SiO[(C₆H5)(CH3)SiO]_mSi(C₆H₅) (CH₃)₂

where m is > 1 , alternatively m is an integer from 1 to 200,

alternatively 1 to 100,

alternatively from 1 to 50,

alternatively from 1 to 10.

[0064] Other suitable polydiorganosiloxanes includes those having the average formula:

(CH₃)2(OH)SiO[(CH3)2SiO]_mSi(OH)(CH₃)2

(CH₃)2(OH)SiO[(C₆H5)(CH3)SiO]_mSi(OH)(CH₃)2 and

(CH₃)(C₆H5)(OH)SiO[(C₆H5)(CH3)SiO]_mSi(OH)(C₆H5)(CH₃)

where m is > 1 , alternatively m is an integer from 1 to 200,

alternatively 1 to 100,

alternatively from 1 to 50,

alternatively from 1 to 10.

[0065] Representative commercially available "linear" organopolysiloxanes include, but are not limited to Dow Corning®704 Fluid, Dow Corning® 705 Fluid, Dow Corning® 710 Fluid, Dow Corning® 510 Fluid, Dow Corning® 550 Fluid, Dow Corning® 2716 Fluid, and Dow Corning® 2666 Fluid.

[0066] The "resin" organopolysiloxane may be selected from those organosiloxane resins comprising at least 60 mole % of [R²Si03/2] siloxy units in its formula, where each R², at each occurrence, is as defined herein. The "resin" organopolysiloxane may contain any amount and combination of other M, D, T, and Q siloxy units, provided the "resin" organopolysiloxane contains at least 60 mole % of [R²Si03/₂] (T units) siloxy units, alternatively the "resin" organopolysiloxane contains at least 70 mole % of [R²Si03/2] siloxy units, at least 80 mole % of [R²SiC>3/2] siloxy units, alternatively the "resin" organopolysiloxane contains at least 90 mole % of [R²Si03/2] siloxy units, or alternatively the "resin" organopolysiloxane contains at least 95 mole % of [R²Si03/₂] siloxy units. In some embodiments, the "resin" organopolysiloxane contains from about 60 to about 100 mole % of [R²Si0₃/2] siloxy units, e.g., from about 60 to about 95 mole % of [R²Si03/₂] siloxy units, from about 60 to about 85 mole % of [R²SiC>3/2] siloxy units, from about 80 to about 95 mole % of [R²Si03/2] units or from about 90 to about 95 mole % of [R²Si03 2].

[0067] Organosiloxane resins containing at least 60 mole % of [R²SiC>3/2] and methods for preparing them are known in the art. In some embodiments, they are prepared by hydrolyzing an organosilane having three hydrolyzable groups on the silicon atom, such as a halogen or alkoxy group in an organic solvent. A representative example for the preparation of a silsesquioxane resin may be found in U.S. Patent No. 5,075,103. Furthermore, many organosiloxane resins are available commercially and sold either as a solid (flake or powder), or dissolved in an organic solvent. Suitable, non-limiting, commercially available organosiloxane resins include; Dow Corning® 217 Flake Resin, 233 Flake, 220 Flake, 249 Flake, 255 Flake, Z-6018 Flake (Dow Corning Corporation, Midland Ml).

Curable compositions

[0068] The present disclosure further provides curable compositions comprising:

a) the organopolysiloxanes, including organosiloxane block copolymers, as described herein, in combination with an alkaline earth metal salt and a condensation catalyst, and

b) an organic solvent (e.g., benzene, toluene, xylene or combinations thereof).

[0069] The alkaline earth metal salt is added to the curable compositions to improve, among other things, thermal stability of compositions (e.g., solid compositions) containing the organopolysiloxanes described herein before they are cured, while they are curing, after they are cured, and/or after heat aging, e.g., heat aging at 200°C for 1000 hours. The improvement in thermal stability may be characterized either qualitatively or quantitatively. For example, the improvements in thermal stability may be assessed qualitatively by visually assessing the change in color of the heat aged cured films (for example, color assessment after aging 1 00 h at 250°C). Alternatively, thermal stability may be assessed quantitatively by techniques such as by determining the temperature (T^) at which a 5 wt. % loss occurs during heating at 5°C/min. Thermal stability may also be assessed quantitatively by measuring the amount of benzene that is produced when the curable compositions described herein are curing and/or after heat aged; or measuring increases in the brittleness of a sample after cure and/or after heat aging (brittleness as determined, e.g., using the Mandrel Test (ASTM D1737)). [0070] The alkaline earth metal salt is combined with the organopolysiloxanes using any suitable method. In some embodiments, the alkaline earth metal salt is first dissolved in a silicon-containing compound {e.g., dimethylsilanol terminal phenylmethyl siloxane fluid having IV HoPhg giv H) before the solution of the alkaline earth metal salt in the silicon-containing compound is combined with the organopolysiloxanes, before or after the condensation catalyst is added. In other embodiments, the alkaline earth metal salt is combined with the organopolysiloxane directly, without the use of a silicon-containing compound, before or after the condensation catalyst is added. In still other embodiments, the alkaline earth metal salt is combined with a solution of the organopolysiloxane(s) in an organic solvent, before or after the condensation catalysts is added to the solution. Regardless of how the alkaline earth metal is combined with the organopolysiloxane(s), in some embodiments, the alkaline earth metal is combined with the organopolysiloxane(s) before the condensation catalyst is added.

[0071 ] As used herein, the term "silicon-containing compound" includes, but is not limited to a silanol-functional siloxane, a silanol-functional silane, an alkoxy- functional siloxane or combinations thereof. In some embodiments, silicon- containing compounds include, but are not limited to, compounds of the formula

R²n(^)ySiO((4-_n-y)/2)_! wherein the subscript n may be from about 0.8 to about 2.2 {e.g., from about 1 to about 2; from about 1 .5 to about 2.2; from about 1 .2 to about 2.2 or from about 1 to about 1 .8); the subscript y may be from about 0.01 to about 3 {e.g., from about 0.01 to about 2, from about 0.05 to about 1 , from about 0.05 to about 0.5, from about 0.05 to about 0.7, from about 2 to about 3, from about 0.5 to about 2.5, from about 1 to about 2.5 or from about 1 .5 to about 2.5); each R² group is, independently, as defined herein; and each X is, at each occurrence, independently H, a halide {e.g., CI, Br and I), -OR³, -NHR3, -NR3R⁴ -OOC-R³, O-

N=CR³R⁴ 0-C(=CR³R⁴)R5 or -N RSCOR⁴, wherein R3, R⁴ and R⁵ are each independently H or a CrC₂o hydrocarbyl group and, in some embodiments, R3 and

R⁴, together with the nitrogen atom to which they are attached, optionally form a cyclic amine.

[0072] As used herein the term "alkaline earth metal salt" includes, but is not limited to, salts of the alkaline earth metals magnesium, calcium, strontium, and barium and includes hydrates and solvates thereof. In some embodiments, the alkaline earth metal salt comprises an alkaline earth metal salt of the formula MX¹ 2 and hydrates (e.g., MX¹2-p H2O, wherein p ranges from 0 to 20, e.g., from 0 to 2, from

2 to 12, from 3 to 1 0, from 1 to 8 or from 0 to 6) and solvates thereof, where M represents an alkaline earth metal and X¹ represents any suitable counterion including halogen (e.g., fluoride, chloride, bromide, and iodide), hydroxide, carbonate, sulfate, phosphate, acetate, benzoate, and the like. In some embodiments, the alkaline earth metal salt comprises an alkaline earth metal hydroxide or an alkaline earth metal hydroxide hydrate of the formula M(OH)2-p

H2O, wherein M represents an alkaline earth metal and p ranges from 0 to 20 (e.g., from 0 to 2, from 2 to 12, from 3 to 1 0, from 1 to 8 or from 0 to 6). Representative examples of alkaline earth metal salts include, but are not limited to barium hydroxide, including the monohydrate, the dehydrate, the trihydrate, the tetrahydrate, the pentahydrate, the hexahydrate, the heptahydrate, the octahydrate, and combinations thereof.

[0073] The amount of the alkaline earth metal salt combined with curable compositions comprising the organopolysiloxane(s) described herein may be any suitable amount and, in some embodiments, an amount sufficient to improve the thermal stability of the curable and/or cured compositions comprising the organopolysiloxane(s). In some embodiments, the amount of alkaline earth metal salt sufficient to improve the thermal stability of the curable and/or cured compositions comprising the organopolysiloxane(s), in terms of alkaline earth metal level as a function of solids, may be from about 25 to about 10,000, e.g., from about 25 to about 5000 ppm, from about 1000 to about 5000, from about 500 to about 2500, from about 30 to about 300 ppm, from about 300 ppm to about 1000 ppm, from about 1 500 ppm to about 3000 ppm, from about 2000 ppm to about 3500 ppm, from about 2000 ppm to about 5000 ppm or from about 2500 ppm to about 3500 ppm. In some embodiments, the alkaline earth metal salt is present in an amount sufficient to provide an amount of alkaline earth metal sufficient to reduce the amount of benzene produced upon cure and/or heat aging by at least 90%, e.g., by at least 95%, by at least 96%, by at least 97%, by at least 98%, by at least 99%, by 100%, from about 90% to about 1 00%, from about 93% to about 99%, from about 95% to about 99% or from about 95% to about 100%. [0074] In some embodiments, the incorporation of the alkaline earth metal salt(s) into the compositions described herein provides solid compositions {e.g., films) that not only have improved thermal stability {e.g., the amount of benzene produced upon cure and/or heat aging is reduced by the amounts described herein), but, due to the presence of the alkaline earth metal salt(s) also have a high refractive index before and/or after curing and/or after heat aging. As used herein, the term "high refractive index" refers to refractive indices greater than 1 .50, e.g., greater than 1 .55, greater than 1 .58, greater than 1 .65, greater than 1 .75; from about 1 .5 to about 2.5; from about 1 .55 to about 1 .65; from about 1 .55 to about 1 .75; from about 1 .6 to about 1 .8, from about 1 .61 to about 1 .75 or from about 1 .62 to about 1 .67.

[0075] In some embodiments, the curable compositions contain a cure catalyst. The cure catalyst may be selected from any catalyst known in the art to effect condensation cure of organosiloxanes, such as various tin or titanium catalysts. Condensation catalyst can be any condensation catalyst that may be used to promote condensation of silicon bonded hydroxy (=silanol) groups to form Si-O-Si linkages. Examples include, but are not limited to, amines and metal ligand complexes of lead, tin, titanium, zinc, and iron. Other examples include, but are not limited to basic compounds, such as trimethylbenzylammonium hydroxide, tetramethylammonium hydroxide, n-hexylamine, tributylamine, diazabicycloundecene (DBU) and dicyandiamide; and metal-containing compounds such as tetraisopropyl titanate, tetrabutyl titanate, titanium acetylacetonate, aluminum triisobutoxide, aluminum triisopropoxide, zirconium tetra(acetylacetonato), zirconium tetrabutylate, cobalt octylate, cobalt acetyl acetonato, iron acetylacetonato, tin acetylacetonato, dibutyltin octylate, dibutyltin laurate, zinc octylate, zinc bezoate, zinc p-tert-butylbenzoate, zinc laurate, zinc stearate, aluminum phosphate, and aluminum triisopropoxide; organic aluminum and titanium chelates, such as aluminum trisacetylacetonate, aluminum bisethylacetoacetate monoacetylacetonate, diisopropoxybis(ethylacetoacetate)titanium, and diisopropoxybis(ethylacetoacetate)titanium. In some embodiments, the condensation catalysts include zinc octylate, zinc bezoate, zinc p-tert- butylbenzoate, zinc laurate, zinc stearate, aluminum phosphate, and aluminum triisopropoxide. See, e.g., U.S. Patent No. 8,193,269, the entire disclosure of which is incorporated by reference as if fully set forth herein. Other examples of condensation catalysts include, but are not limited to aluminum alkoxides, antimony alkoxides, barium alkoxides, boron alkoxides, calcium alkoxides, cerium alkoxides, erbium alkoxides, gallium alkoxides, silicon alkoxides, germanium alkoxides, hafnium alkoxides, indium alkoxides, iron alkoxides, lanthanum alkoxides, magnesium alkoxides, neodymium alkoxides, samarium alkoxides, strontium alkoxides, tantalum alkoxides, titanium alkoxides, tin alkoxides, vanadium alkoxide oxides, yttrium alkoxides, zinc alkoxides, zirconium alkoxides, titanium or zirconium compounds, especially titanium and zirconium alkoxides, and chelates and oligo- and polycondensates of the above alkoxides, dialkyltin diacetate, tin(ll) octoate, dialkyltin diacylate, dialkyltin oxide and double metal alkoxides. Double metal alkoxides are alkoxides containing two different metals in a particular ratio. In some embodiments, the condensation catalysts include titanium tetraethylate, titanium tetrapropylate, titanium tetraisopropylate, titanium tetrabutylate, titanium tetraisooctylate, titanium isopropylate tristearoylate, titanium truisopropylate stearoylate, titanium diisopropylate distearoylate, zirconium tetrapropylate, zirconium tetraisopropylate, zirconium tetrabutylate. See, e.g., U.S. Patent No. 7,005,460, the entire disclosure of which is incorporated by reference as if fully set forth herein. In addition, the condensation catalysts include titanates, zirconates and hafnates as described in DE 4427528 C2 and EP 0 639 622 B1 , both of which are incorporated by reference as if fully set forth herein.

[0076] In some embodiments, the condensation catalyst comprises metal- containing complexes. The molar ratio of the metal in the metal-containing catalyst to the alkaline earth metal is about 1 :10, e.g., about 1 :5, about 1 :8, about 1 :4, about 2:3, about 1 :2, from about 1 :10 to about 1 :2, from about 1 :2 to about 2:3, from about 1 :4 to about 2:3 or from about 1 :4 to about 3:4.

[0077] Solid compositions containing the organopolysiloxanes described herein may be prepared by removing the solvent from the curable compositions as described herein. The solvent may be removed by any known processing techniques. In one embodiment, a film of the curable compositions containing the organosiloxane block copolymers is formed, and the solvent is allowed to evaporate from the film. Subjecting the films to elevated temperatures, and/or reduced pressures, will accelerate solvent removal and subsequent formation of the solid curable composition. Alternatively, the curable compositions may be passed through an extruder to remove solvent and provide the solid composition in the form of a ribbon or pellets. Coating operations against a release film could also be used as in slot die coating, knife over roll, rod, or gravure coating. Also, roll-to- roll coating operations could be used to prepare a solid film. In coating operations, a conveyer oven or other means of heating and evacuating the solution can be used to drive off the solvent and obtain the final solid film.

[0078] The present disclosure further relates to solid forms of the aforementioned organopolysiloxanes described herein and solid compositions derived from the curable compositions described herein.

[0079] In some embodiments, the aforementioned organopolysiloxanes are isolated in a solid form, for example by casting films of a solution of the organopolysiloxane(s) in an organic solvent {e.g., benzene, toluene, xylene or combinations thereof) and allowing the solvent to evaporate. Under these conditions, the aforementioned organosiloxane block copolymers can be provided as solutions in an organic solvent containing from about 50 wt. % to about 80 wt. % solids, e.g., from about 60 wt. % to about 80 wt. %, from about 70 wt. % to about 80 wt. % or from about 75 wt. % to about 80 wt. % solids. In some embodiments, the solvent is toluene. In some embodiments, such solutions will have a viscosity of from about 1500 cSt to about 4000 cSt at 25^°C, e.g., from about 1500 cSt to about 3000 cSt, from about 2000 cSt to about 4000 cSt or from about 2000 cSt to about 3000 cSt at 25^°C.

[0080] Upon drying or forming a solid, the non-linear blocks of the block copolymer may further aggregate together to form "nano-domains." As used herein, "predominately aggregated" means the majority of the non-linear blocks of the organosiloxane block copolymer are found in certain regions of the solid composition, described herein as "nano-domains." As used herein, "nano-domains" refers to those phase regions within the solid block copolymer compositions that are phase separated within the solid block copolymer compositions and possess at least one dimension sized from 1 to 1 00 nanometers. The nano-domains may vary in shape, providing at least one dimension of the nano-domain is sized from 1 to 100 nanometers. Thus, the nano-domains may be regular or irregularly shaped. The nano-domains may be spherically shaped, tubular shaped, and in some instances lamellar shaped.

[0081 ] In a further embodiment, the solid organosiloxane block copolymers as described herein contain a first phase and an incompatible second phase, the first phase containing predominately the disiloxy units [R¹2Si02/2] as defined above, the second phase containing predominately the trisiloxy units [R²SiC>3/2] as defined above, the non-linear blocks being sufficiently aggregated into nano- domains which are incompatible with the first phase.

[0082] When solid compositions are formed from the curable compositions of an organosiloxane block copolymer, which also contain an organosiloxane resin, as described herein, the organosiloxane resin may also predominately aggregate within the nano-domains.

Filler

[0083] The curable compositions of the present disclosure may further contain a filler, as an optional component. The filler may comprise a reinforcing filler, an extending filler, a conductive filler, or a combination thereof. For example, the composition may optionally further comprise a reinforcing filler, which, when present, may be added in an amount ranging from about 0.1 % to about 95 %, e.g., from about 2% to about 90%, from about 1 % to about 60 %; from about 25% to about 60%; from about 30% to about 60%; from about 40% to about 60%; from about 50 to about 60%; from about 25% to about 50%; from about 25% to about 40%; from about 25% to about 30%; from about 30% to about 40%; from about 30% to about 50%; or from about 40% to about 50%; based on the total weight of the composition.

[0084] The exact amount of the filler may depend on various factors including the form of the reaction product of the composition and whether any other fillers are added. In some embodiments, the amount of filler may depend on a target hardness or modulus for, e.g., a solid compositions described herein, such that higher target hardness and/or modulus may require higher filler loadings. Non- limiting examples of suitable reinforcing fillers include carbon black, zinc oxide, magnesium carbonate, aluminum silicate, sodium aluminosilicate, and magnesium silicate, as well as reinforcing silica fillers such as fume silica, silica aerogel, silica xerogel, and precipitated silica. Fumed silicas are known in the art and commercially available; e.g., fumed silica sold under the name CAB-O-SIL by Cabot Corporation of Massachusetts, U.S.A.

[0085] The composition may optionally further comprise an extending filler in an amount ranging from about 0.1 % to about 95%, e.g., from about 2% to about 90%, from about 1 % to about 60%; from about 1 to about 20%; from about 25% to about 60%; from about 30% to about 60%; from about 40% to about 60%; from about 50% to about 60%; from about 25% to about 50%; from about 25% to about 40%; from about 25% to about 30%; from about 30% to about 40%; from about 30% to about 50%; or from about 40% to about 50%; based on the total weight of the composition. Non-limiting examples of extending fillers include crushed quartz, aluminum oxide, magnesium oxide, calcium carbonate such as precipitated calcium carbonate, zinc oxide, talc, diatomaceous earth, iron oxide, clays, mica, chalk, titanium dioxide, zirconia, sand, carbon black, graphite, or a combination thereof. Extending fillers are known in the art and commercially available; such as a ground silica sold under the name MIN-U-SIL by U.S. Silica of Berkeley Springs, WV. Suitable precipitated calcium carbonates include Winnofil® SPM from Solvay and Ultrapflex® and Ultrapflex® 100 from SMI.

[0086] The composition may optionally further comprise a conductive filler in an amount ranging from about 0.1 % to about 95%, e.g., from about 2% to about 90%, from about 1 % to about 60%; from about 1 % to about 20%; from about 25% to about 60%; from about 30% to about 60%; from about 40% to about 60%; from about 50% to about 60%; from about 25% to about 50%; from about 25% to about 40%; from about 25% to about 30%; from about 30% to about 40%; from about 30% to about 50%; or from about 40% to about 50%; based on the total weight of the composition. Conductive fillers may be thermally conductive, electrically conductive, or both. Conductive fillers are known in the art and include metal particulates (such as aluminum, copper, gold, nickel, silver, and combinations thereof) ; such metals coated on nonconductive substrates; metal oxides (such as aluminum oxide, beryllium oxide, magnesium oxide, zinc oxide, and combinations thereof), meltable fillers {e.g., solder), aluminum nitride, aluminum trihydrate, barium titanate, boron nitride, carbon fibers, diamond, graphite, magnesium hydroxide, onyx, silicon carbide, tungsten carbide, and a combination thereof. Alternatively, other fillers may be added to the composition, the type and amount depending on factors including the end use of the cured product of the composition. Examples of such other fillers include magnetic particles such as ferrite; and dielectric particles such as fused glass microspheres, titania, and calcium carbonate.

[0087] In one embodiment, the filler comprises alumina. Phosphor

[0088] The curable compositions of the present disclosure may include a phosphor. The phosphor is not particularly limited and may include any known in the art. In one embodiment, the phosphor is made from a host material and an activator, such as copper-activated zinc sulfide and silver-activated zinc sulfide. Suitable but non- limiting host materials include oxides, nitrides and oxynitrides, sulfides, selenides, halides or silicates of zinc, cadmium, manganese, aluminum, silicon, or various rare earth metals. Additional suitable phosphors include, but are not limited to, Zn₂Si04:Mn (Willemite); ZnS:Ag+(Zn,Cd)S:Ag; ZnS:Ag+ZnS:Cu+Y202S:Eu ZnO:Zn; KCI; ZnS:Ag,CI or ZnS:Zn; (KF,MgF₂):Mn; (Zn,Cd)S:Ag or (Zn,Cd)S:Cu Y20₂S:Eu+Fe₂03, ZnS:Cu,AI; ZnS:Ag+Co-on-AI₂0₃;(KF,MgF2):Mn

(Zn,Cd)S:Cu,CI; ZnS:Cu or ZnS:Cu,Ag; MgF₂:Mn; (Zn,Mg)F₂:Mn; Zn₂Si0₄:Mn,As ZnS:Ag+(Zn,Cd)S:Cu; Gd₂0₂S:Tb; Y₂0₂S:Tb; Y₃AI₅0₁₂:Ce; Y₂Si0₅:Ce Y₃AI₅0-|₂:Tb; ZnS:Ag,AI; ZnS:Ag; ZnS:Cu,AI or ZnS:Cu,Au,AI (Zn,Cd)S:Cu,CI+(Zn,Cd)S:Ag,CI; Y₂Si0₅:Tb; Y₂OS:Tb; Y₃(AI,Ga)₅0₁₂:Ce Y₃(AI,Ga)₅0₁₂:Tb; lnB0₃:Tb; lnB0₃:Eu; lnB0₃:Tb+lnB0₃:Eu lnB0₃:Tb+lnB0₃:Eu+ZnS:Ag; (Ba,Eu)Mg₂AI-| ₆0₂7; (CeJbJMgA^ -|Oig BaMgAI-|oOi7:Eu,Mn; BaMg₂AI-| 60₂7:Eu(ll); BaMgAlinO-|7:Eu,Mn

BaMg₂AI-| ₆0₂7:Eu(ll),Mn(ll); Ce₀.67Tb₀.₃₃ gAI-| O ₉:Ce,Tb Zn₂Si04:Mn,Sb₂0₃; CaSi0₃:Pb,Mn; CaW04 (Scheelite); CaW04:Pb; MgW04 (Sr,Eu,Ba,Ca)₅(P0₄)₃CI; Sr₅CI(P0₄)₃:Eu(ll); (Ca,Sr,Ba)₃(P0₄)₂CI₂:Eu (Sr,Ca,Ba)₁₀(PO₄)₆CI₂:Eu; Sr₂P20₇:Sn(ll); Sr₆P₅BO₂₀:Eu; Ca₅F(P0₄)₃:Sb (Ba,Ti)₂P₂07:Ti; 3Sr₃(P0₄)₂.SrF₂:Sb,Mn; Sr₅F(P0₄)₃:Sb,Mn

Sr₅F(P04)₃:Sb,Mn; LaP0₄:Ce,Tb; (La,Ce,Tb)P0₄;(La,Ce,Tb)P0₄:Ce,Tb Ca₃(P04)₂.CaF₂:Ce,Mn; (Ca,Zn,Mg)₃ (P04)₂:Sn; (Zn,Sr)₃(P04)₂:Mn (Sr,Mg)₃(P0₄)₂:Sn; (Sr,Mg)₃(P0₄)₂:Sn(ll); Ca₅F(P0₄)₃:Sb,Mn

Ca₅(F,CI)(P0₄)₃:Sb,Mn; (Y,Eu)₂0₃; Y₂0₃:Eu(lll); Mg₄(F)Ge0₆:Mn Mg₄(F)(Ge,Sn)0₆:Mn; Y(P,V)0₄:Eu; YV0₄:Eu; Y₂0₂S:Eu; 3.5 MgO · 0.5 MgF₂ - Ge0₂ :Mn; Mg₅As₂0-| i :Mn; SrAI₂0₇:Pb; LaMgAI-| -|0₁₉:Ce; LaP0₄:Ce SrAI₁₂0-|g:Ce; BaSi₂0₅:Pb; SrFB₂0₃:Eu(ll); SrB₄0₇:Eu; Sr₂MgSi₂0₇:Pb MgGa₂0₄:Mn(ll); Gd₂0₂S:Tb; Gd₂0₂S:Eu; Gd₂0₂S:Pr; Gd₂0₂S:Pr,Ce,F Y₂0₂S:Tb; Y₂0₂S:Eu; Y 0₂S:Pr; Zn(0.5)Cd(0.4)S:Ag; Zn(0.4)Cd(0.6)S:Ag;

CdW0₄; CaW0₄; MgW0₄; Y₂Si0₅:Ce;YAI0₃:Ce; Y₃AI₅0_{1 2}:Ce;

Y₃(AI,Ga)₅0₁ :Ce; CdS:ln ; ZnO:Ga; ZnO:Zn ; (Zn,Cd)S:Cu,AI ; ZnS:Cu,AI,Au;

ZnCdS:Ag,Cu ; ZnS:Ag; anthracene, EJ-212, Zn₂Si04:Mn; ZnS:Cu ; Nal :TI ; CshTI ; LiF/ZnS:Ag; LiF/ZnSCu,AI,Au, and combinations thereof.

[0089] The amount of phosphor added to the present compositions may vary and is not limiting. When present, the phosphor may be added in an amount ranging from about 0.1 % to about 95%, e.g., from about 5% to about 80%, from about 1 % to about 60%; from about 25% to about 60%; from about 30% to about 60%; from about 40% to about 60%; from about 50% to about 60%; from about 25% to about 50%; from about 25% to about 40%; from about 25% to about 30%; from about 30% to about 40%; from about 30% to about 50%; or from about 40% to about 50%; based on the total weight of the composition.

[0090] Some of the embodiments of the present invention relate to optical assemblies and articles comprising the compositions described herein such as those described in PCT/US2012/07101 1 , filed December 20, 2012; PCT/US2013/021 707, filed January 1 6, 2013; and PCT/US2013/0251 26, filed February 7, 201 3, all of which are incorporated by reference as if fully set forth herein. Accordingly, some embodiments of the present invention relate to an LED encapsulant comprising an organopolysiloxane, such as those described herein.

[0091 ] The term "about," as used herein, can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1 % of a stated value or of a stated limit of a range.

[0092] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range were explicitly recited. For example, a range of "about 0.1 % to about 5%" or "about 0.1 % to 5%" should be interpreted to include not just about 0.1 % to about 5%, but also the individual values (e.g., 1 %, 2%, 3%, and 4%) and the sub-ranges [e.g., 0.1 % to 0.5%, 1 .1 % to 2.2%, 3.3% to 4.4%) within the indicated range.

[0093] Embodiments of the invention described and claimed herein are not to be limited in scope by the specific embodiments herein disclosed, since these embodiments are intended as illustration of several aspects of the disclosure. Any equivalent embodiments are intended to be within the scope of this disclosure. Indeed, various modifications of the embodiments in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

[0094] The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

EXAMPLES

[0095] The following examples are included to demonstrate specific embodiments of the invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. All percentages are in wt. %. All measurements were conducted at 23-C unless indicated otherwise.

Example 1 : Preparation of (PhMeSi02/2)o.52(^PnSi03/2)o.42 (^{45 wt}- ^% Phenyl-T)

[0096] A 500 mL 4-neck round bottom flask was loaded with Dow Corning 217 Flake (45.0 g, 0.329 moles Si) and toluene (Fisher Scientific, 70.38 g). The flask was equipped with a thermometer, Teflon stir paddle, and a Dean Stark apparatus attached to a water-cooled condenser. A nitrogen blanket was applied; the Dean Stark apparatus was prefilled with toluene; and an oil bath was used for heating. The reaction mixture was heated at reflux for 30 minutes. After cooling the reaction mixture to 108°C, a solution of diacetoxy terminated PhMe siloxane was added quickly.

[0097] The diacetoxy terminated PhMe siloxane was prepared by adding a 50/50 wt. % MTA/ETA (methyltriacetoxysilane/ethyltriacetoxysilane) (1 .21 g, 0.00523 moles Si) mixture to a solution of 140 dp silanol terminated PhMe siloxane (55.0 g, 0.404 moles Si) dissolved in toluene (29.62 g). The solution was mixed for 2 hours at room temperature under a nitrogen atmosphere.

[0098] After the diacetoxy terminated PhMe siloxane was added, the reaction mixture was heated at reflux for 2 hours. At this stage 50/50 wt. % MTA/ETA (7.99 g, 0.0346 moles Si) was added at 108°C. The reaction mixture was heated at reflux for an additional 1 hour. The reaction mixture was cooled to 90°C and then deionized (Dl) water (12 mL) was added. The temperature was increased to reflux and the water was removed by azeotropic distillation. The reaction mixture was cooled again to 90°C and more Dl water (12 mL) was added. The reaction mixture was once again heated up to reflux and the water was removed. Some toluene (56.9 g) was then removed by distillation to increase the solids content. The material was cooled to room temperature and then pressure filtered through a 5.0 μηπ filter. Sheets were cast (made by pouring the solution in a chase and evaporating the solvent) and they were optically clear.

Example 2 - Preparation of barium-containing compositions

[0099] In an open flask with a mechanical stirrer and heating oil bath, a set amount of Ba(OH)2"P H2O solid was added into about 50 grams of a dimethylsilanol terminal phenylmethyl siloxane fluid

^ar|d ^mi^xecl to form a dispersion. This mixed dispersion was kept at 130-140°C for 30-45 minutes to form a colorless uniform solution, and then cooled down to obtain the product. See Table 1 . The barium content was measured by inductively coupled plasma (ICP) spectrometer.

Table 1

[00100] The resin-linear material from Example 1 , prepared as a 75% solution in toluene, was mixed with compositions listed in Table 1 at 3 wt. % vs. resin-linear solids using a planetary mixer, followed by addition of a cure catalyst as shown in Table 2. In instances where Ce:YAG phosphor was used, 1 g of resin-linear solution to 1 g of Ce:YAG particles were mixed in a planetary mixer.

Table 2

Comparative 4 none 50 ppm DBU None

Comparative 5 none 50 ppm DBU Ce:YAG

[00101] The thermal stability data are shown below in Table 3.

Table 3

¹ Benzene was measured from headspace gas chromotagraphy (ppm of benzene in the headspace per solid material)

n.m. = not measured.

²Extent of Si-Phenyl scission on PhMe-D units was determined from attenuated total reflectance infrared spectroscopy by taking the ratio between the 1290 to 1271 cm^"1 region and the 1290 to 1235 cm^"1 region, multiplied by 100.

^Weight loss was determined using thermogravimetric analysis under an air atmosphere (50mL/min).

⁴Cure time was determined from oscillatory shear rheology at 1 Hz and 5% strain, ramp from 120°C to 150°C in 10min and hold at 150°C, cure speed was determined as the time to reach tan d of 1 (time = 0 was at the start of the experiment at 120°C).

[00102] The results shown in Table 3 demonstrate that alkaline earth metal salts reduce benzene generation both in the absence and presence of Lewis acid metal catalysts like Al(acac)3- Weight loss is also reduced as the alkaline earth metal salt content is increased.

In fact, the thermal stability (and cure speeds) of Lewis acid metal-containing compositions containing sufficient amounts of alkaline earth metal salt approach the thermal stability levels observed for condensation catalysts that produce very little benzene and/or exhibit very little weight loss, such as DBU, even in the presence of a phosphor. See Comparative 4 and compare to Sample 7.

Claims

What is Claimed is:

1 . A curable composition comprising:

i) an organosiloxane block copolymer comprising:

40 to 90 mole percent disiloxy units of the formula [R¹2S1O2/2],

1 0 to 60 mole percent trisiloxy units of the formula [R²SiC>3/2],

0.5 to 35 mole percent silanol groups [≡SiOH];

wherein :

each R¹ , at each occurrence, is independently a C-| to C30 hydrocarbyl,

each R², at each occurrence, is independently a C-| to C30 hydrocarbyl;

wherein :

ii) an organopolysiloxane comprising unit formula:

[R¹ 3Si0₁/2]c[R¹2Si02 2]d[R¹ Si0₃/2]e[Si04 2]f

ii) an alkaline earth metal salt; and

iii) a condensation catalyst.

The curable composition of claim 1 , wherein the condensation catalyst comprises metal ligand complex.

3. The curable composition of claim 2, wherein the metal ligand complex comprises a metal acetylacetonate complex, wherein the metal is Al, Bi, Sn, Ti or Zr.

4. The curable composition of claim 3, wherein the metal ligand complex comprises aluminum trisacetylacetonate.

5. The curable composition of claim 1 , wherein the condensation catalyst

comprisesdiazabicycloundecene (DBU).

6. The curable composition of any preceding claim, wherein is phenyl.

7. The curable composition of any preceding claim, wherein R1 is methyl or phenyl.

8. The curable composition of any preceding claim, wherein the disiloxy units have the formula [(Ch^XCgHySiC^]-

9. The curable composition of any preceding claim, wherein the disiloxy units have the formula [(CH₃)₂Si0₂/2]-

10. The curable composition of any preceding claim, wherein the alkaline earth metal salt comprises an alkaline earth metal hydroxide or an alkaline earth metal hydroxide hydrate of the formula M(OH)2-p H2O wherein M represents an alkaline earth metal and p ranges from 0 to 8.

1 1 . The curable composition of claim 10, wherein M is barium.

12. The curable composition of any preceding claim, wherein the alkaline earth metal salt is present, in terms of alkaline earth metal level as a function of solids, in an amount from about 25 ppm to about 10,000 ppm.

13. The curable composition of any preceding claim, wherein 0.2≤ c+d+e+f < 1.

14. The curable composition of any preceding claim, wherein the condensation catalyst comprises a metal ligand complex and the molar ratio of the metal in the metal-ligand complex to the alkaline earth metal is from about 1 :4 to about 3:4.

15. A solid film composition comprising the curable composition of any preceding claim.

16. The solid film composition of claim 15, wherein the solid composition has an optical transmittance of at least 95%.

17. The cured product of the composition of any preceding claim.

18. A method for increasing the thermal stability of a curable composition comprising: i) a condensation catalyst; and

ii) an organosiloxane block copolymer comprising:

40 to 90 mole percent disiloxy units of the formula [R¹2S1O2/2].

1 0 to 60 mole percent trisiloxy units of the formula [R²Si03/2],

0.5 to 35 mole percent silanol groups [≡SiOH];

wherein :

each R¹ , at each occurrence, is independently a C-| to C30 hydrocarbyl,

each R², at each occurrence, is independently a C-| to C30 hydrocarbyl;

wherein :

an organopolysiloxane comprising unit formula:

[R¹ 3Si0₁/2]c[R¹2Si02/2]d[R¹ Si03/2]e[Si0₄ 2]f

the method comprising contacting the curable composition with an alkaline earth metal salt.

19. The method of claim 18, wherein the increase in thermal stability comprises a

reduction in the production of benzene upon curing and/or heat aging the curable composition.

20. The method of claim 19, wherein the alkaline earth metal salt is present, in terms of alkaline earth metal level as a function of solids, in an amount from about 25 ppm to about 10,000 ppm.