CA1225774A - Thermoplastic molding compositions - Google Patents

Abstract

Mo-2494 THERMOPLASTIC MOLDING COMPOSITIONS
ABSTRACT OF THE DISCLOSURE
The present invention is directed to thermo-plastic molding compositions comprising a blend of poly(ethylene terephthalate) and polycarbonate resins characterized in that the weight ratio between said resins is about 1:1 to 4:1 and in that a graft modified polybutadiene rubber is added thereto, said compositions exhibiting an improved level of impact strength.
Mo-2494

Description

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Mo-2494 THERMOPLASTIC MOLDING COMPOSITIONS
Field of the Invention .. .. . .
The invention relates to thermoplastic molding compositions and in particular, to impact modified blends of polyethylene terephthalate and polycarbonate resin.
BACKGROUND OF T~E INVENTION
Improved properties and processability of polycarbonate has been disclosed in U.S. 3,130,177 and 3,162,695 to result upon the blending therewith a butadiene graft polymer; blends of polycarbonate and polyester, modified by a butadiene graft copolymer were disclosed in U.S. 3,~64,428. Also, similar systems were disclosed in U.S. 4,180,494 to offer improved solvent resistance.
The present invention is based on the surprising and unexpected level of impact strength, especially at low temperatures, assoclated with a particulflr composition comprising polyethylene terephthalate and polycarbonate resins having a certain weight ratio therebetween and a particular graft elastomer which is characterized in that 0 its elastomeric core is predominantly o polybutadiene.
SUMMARY OF THE INVENTION
The present invention is directed to thermoplastic molding compositions comprising a blend of poly(ethylene terephthalate) and polycarbonate resins characterized in that the weight ratio between said resins is about l:l to 4:1 and in that a graft modified polybutadiene rubber is added thereto, said compositions exhibiting an improved level of impact strength.
DETAILED DESCRIPTION OF THE INVENTION
AND ITS PREFERRED EMBODIMENTS
The high molecular weight, thermoplastic polyester resins suitable in the practice of the Mo-2494 . ~

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invention are derived from a terephthalic acid com-ponent and an ethylene glycol component and are charac-terized in that their intrinsic viscosity is at least 0.4 deciliters per gram. Optionally, the terephthallc acid accounts for at least 85 mole percent of the acid component. Among the suitable other, optional dicar-boxylic acids are isophthalic acid, naphthalene-dicar-boxylic acid, diphenylether dicarboxylic acid, diphenyl-dicarboxylic acid, dlphenylsulfone dlcarboxyllc acid and diphenoxyethane dicarboxylic acid. Other optlonal acids include hydroxycarboxylic acids and aliphatic dicarboxylic acids such as succinic acid, adipic acid and sebacic acid.
The diol component of these polyesters may, in additlon to ethylene ~lycol., contain Up to 30 mole percent of other dlols having up to 4 carbon atoms in the ~orm of linear methylene chains, cycloaliphatic diols ha~ing from 6 to ]5 carbon atoms or aromatic diols having from 6 to 21 carbon atoms. Examples of such additional diols ("codiols") include 3-methyl-pen~anediol-(2,4), 2-methylpentanediol-(1,4), 2,2,4-tri-methylpentanediol-(1,3), 2-ethylhexanediol-(1,3),

2,2-diethylpropanediol-(1,3), hexanedlol-(1,3), 1,4-dl-(~-hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclo-hexyl)-propane, 2,4-dihydroxy-1,1,3,3-tetramethylcyclo-butane, 2,2-bls-(3-~-hydroxyethoxyphenyl)-propane and 2,2-bis-(4-hydroxypropoxyphenyl)-propane.
Typical examples of the diol include tri-methylene glycol, tetramethylene glycol and hexa-methylene glycol, neopentyl glycol, cyclohexane di-methylol, tricyclodecane dimethylol, 2,2-bis-(4-~-hydroxyethoxyphenyl)-propane, 4,4'-bis-(~-hydroxy-ethoxy)-diphenylsulfone, and diethylene glycol.

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The polyesters may be branched by incorpor-ating trihydric or tetrahydric alcohols or tribasic or tetrabasic acids 9 as described in German Offenlegungs-schrift 1,900,270 and in U.S. Patent 3,962,744.
Examples of suitable branching agents include trimesic acid, pyromellitic acid, trimethylolpropane and ethane, and pentaerythritol. It is advisable to use no more than 1 mole percent of branching agent, based on the quantity of acid component. The polyesters may also contain known monofunctional compounds such as phenol or benzoic acid as chain terminators.
The preferred polyesters are characterized in that their structure comprises units of the general formula (I):
O
O C
~C~12) -O-C

wherein n denotes 2.
The intrinsic viscosity characterizing the suitable polyester resin in the practice according to the invention should preferably be in the range of 0.4 to 1.4 grams per deciliter and, more preferably, bet-ween 0.4 and 1.1 grams per deciliter, as measured in a 1% solution of phenol and tetrachloroethane (60:40) at Methods for the preparation of the polyester resin suitable in the present context are known and have been described in U.S. Patents 2,463,319 and 3,047,539.

Mo-2494 ~2~577 The composition of the invention may include crystallization rate promoters for the polyester (such as oligomeric polyesters) to allow lower mold temperatures and shorter injection cycles. Suitable promoters have been taught in U.S. Patent 4,223,113.
The most preferred poly(alkylene terephthalate) in the present context is poly(ethylene terephthalate).
The polycarbonate resins useful in the practice of the invention are homopolycarbonate, copolycarbonate and terpolycarbonate resins or mixtures thereof. The polycarbonate resins generally have molecular weights of 10,000-200,000 (weight average molecular weight) pre~erably 20,000-80,000, and are additionally characterized by their melt flow of 1-24 gm/10 min. at 300C per ~STM D-1238.
These polycarbonate resins may be prepared, for example, by the known diphaslc lnterface process firom phosgene and dihydroxy compounds by polycondensation (see the monograph ~l. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York, 1964).
In the present context, dihydroxy compounds suitable for the preparation of the polycarbonates of the invention conform to the structural formula (1) or (2) / ~3 O~I ( 1 ) /_ (Z)d e ~IO~ d HO ~ )f (2) wherein Mo-2494 ^ ~:
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denotes an alkylene group with 1 to 8 carbon atoms, an alkylidene group with 2 to 8 carbon atoms, a cycloalkylene group with 5 to 15 carbon atoms, a cycloalkylidene group with 5 to 15 carbon atoms, a carbonyl group, an oxygen atom, S, -SO- or -SO2- radical, a radical of the general formula CH~ ~ CH3 ~ 3 r__ C
-- C ~C-- or --C--~> CH3 g denotes the number of 0 or 1;
e denotes the number of 0 or 1;
denotes F, Cl, Br or Cl-C2 alkyl and if severa]. Z are substituents in one aryl radi.cal, the~ may be identical or different;
d denotes 0 or an integer of from 1 to 4; and f denotes 0 or an integer of from 1 to 3.
Among the useful dihydroxy compounds in the practice of the invention are hydroquinone, resorcinol, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)-cyclo-alkanes, bis-(hydroxyphenyl)-ethers, bis-(hydroxy-phenyl)-ketones, bis-(hydroxyphenyl)-sulfoxides, bis-(hydroxyphenyl)-sulfones and d,~-bis-(hydroxyphenyl)-di-isopropyl-benzenes. These and further suitable aromatic dihydroxy compounds are described, for example, in ~.S.
Patents 3,028,365; 2,999,835; 3,148,172; 3,2.71,358;
2,991,273; 3,271,367; 3,280,078; 3,014,891 and 2,999,846, in German Offenlegungsschriften (German Published Specifications) 1,570,703; 2,063,050, 2,063,052, 2,211,956 and 2,211,957, in French Patent Mo-2494 , ~, .. ...
t`'; ' ' ~ 7 Specification 1,561,418 and in the monograph, H. Sclmell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York, 1964. Further examples of suitable bisphenols are 2,2-bis-(4-hydroxy-phenyl)-propane (bisphenol A), 2,4-bis-(4-hydroxy-phenyl)-2-methylbutane, 1,1-bis-(4-hydroxyphenyl)-cyclo-hexane, a,a-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, 2,2-bis-(3-chloro-4-hydroxyphenyl)-propane, hydroxy-benzophenone and 4,4'-sulfonyl diphenol.
The most preferred bisphenol is 2,2-bis(4-hydroxyphenyl)-propane (bisphenol A).
The polycarbonates of the invention may entail in their structure, units derived from one or more of the suitable bisphenols.
The preparation of polycarbonate resins may be carried out in accorda~ce wlth any o~ the processes known in the art, for e~ample, by the interfacial poly-condensation process, polycondensation in a homogeneous phase or by transesterification.
The suitable processes and the associated reactants, catalysts, solvents and conditions are known in the art and have been described, inter alia, in German Patents 1,046,311 and 962,274 and in U.S.
Patents 3,248,414; 3,153,008; 3,215,668; 3,187,065;
3,028,365; 2,999,846; 2,999,835; 2,964,974; 2,970,137;
3,912,638 and 1,991,273.
In the preparation of the polycarbonate resins of the invention, monofunctional reactants such as monophenols may be used in order to limit their respective molecular weights. Also, branching agents may be emp]oyed. Branching may be obtained by the incorporation of small amounts, preferably of be~ween about 0.05 and 2.0 mol percent (relative to diphenols employed), of trifunctional or more than trifunctional Mo-2494 ~2Z~

compounds, especially compounds having three or more phenolic hydroxyl groups. Polycarbonates of this type are described, for example, in German Offenlegungs-schriften (German Published Specifications) 1,570,533;
5 1,595,762; 2,116,974 and 2,113,347, British Specifi-cation 1,079,821 and U.S. Patent 3,544,514.
Some examples of compounds with three or more than three phenolic hydroxyl groups which can be used are phloroglucinol, 4,6-dimethyl-2,4,6-tri-(4-hydroxy-phenyl)-heptane, 2,4,6-trimethyl-2,4,6-tri-(4-hydroxy-phenyl)-heptane, 1,4,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, tri-(4-hydroxy-phenyl)-phenylmethane, 2,2-bis-[4,4-bis-(4-hydroxy-phenyl)-cyclohexyl]-propane, 2,4-bis-(4-hydroxypllenyl-isopropyl)-phenol, 2,6-bis-(2-hyclroxy-5'-methylbenzyl)-

4-methylphenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxy-phenyl)-propane, hexa(4-(4-hydroxyphenylisopropyl)-phenyl)-orthoterephthalic acid ester, tetra-(4-hy-droxyphenyl)-methane, tetra-(4-(4-hydroxyphenyliso-propyl)-phenoxy)-methane and 1,4-bis((4'-4"-dihydroxy-triphenyl)-methyl)-benzene. Some of the other tri-functional compounds are 2,4-dihydroxy-benzoic acid, trimesic acid, cyanuric chloride and 3,3-bis-(4-hydroxy-phenyl)-2-oxo-2,3-dihydroindole.
Among the resins suitable in the practice of the invention are included phenolphthalein based poly-carbonate, copolycarbonates and terpolycarbonates such as are described in U.S. Patents 3,036,036 and 4,210,741.
The graft elastomer suitable in the present context is characterized in that its core is substantially of polybutadiene and that its grafted phase comprises styrene and acrylonitrile, and further in that the polybutadiene content of the graft elastomer Mo-2494 ,~ ~
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is at least 60%, preferably ~5 to 90%, relative to the weight of the graft elastomer. In these grafts, a monomer mixture of styrene and acrylonitrile is graft polymerized onto the prepolymerized rubber cure; cross-linking of the rubber core is an optional feature of thegraft elastomer of the invention.
Suitable rubbers are polybutadiene, butadiene/
styrene copolymers having up to 30% by weight of co-polymerized styrene, copolymers of butadienes and acryl-onitrile with up to 20% by weight of acrylonitrile andcopolymers of butadiene with up to 20% by weight of a lower alkyl ester of an acrylic or methacrylic acid (for example, methylacrylate, ethylacrylate, methylmeth-acrylate and ethylmethacrylate).
The welght ratio of the rubbery core to the gra~ted phase i.9 wlthin the range of ~0:20 to about 60:~0.
The preparation of graft elastomers of the type suitable in the present context has been described in the art, for instance, in U.S. 3,238,275 and in 3,919,353.
Essentially, the molecules of acrylonitrile-butadiene-styrene (ABS) graft polymers consist of two or more polymeric parts of different compositions chem-ically united. The graft polymers may be prepared bypolymerizing at least one conjugated diene, such as butadiene, or a conjugated diene with a monomer polymer-izable therewith, such as noted above to provide a backbone (a core) with subsequent polymerization of at least one grafting monomer, and preferably two, in the presence of the prepolymerized backbone to complete the graft polymer.

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--g The backbone, as mentioned, is preferably a conjugated diene polymer or copolymer such as polybuta-diene, a butadiene-styrene, butadiene-acrylonitrile or the like.
A specific conjugated diene monomer which may be utilized in preparing the backbone of the graft polymer is generically described by the formula:
x x x c = C - C = C /
X/ \X

wherein X may be selected from the group consisting of hydrogen, alkyl groups containing from 1 to 5 carbon atoms, chloro and bromo. Examples of dienes that may be used are butadiene; isoprene; 1,2-heptadiene;
methyl-1,3-pentadiene; 2,3-dimethyl-1,3-butadiene;
1,3-pentadiene; 2-methyl-3-ethyl-1,3-blltadiene;
2-ethyl-1,3-pentadiene; 1,3- and 2,4-hexadiene, chloro-and bromo-substituted butadienes such as dichlorobuta-diene, bromobutadiene, chloroprene, dibromobutadiene, mixtures thereof and the like. The preferred conjugated diene utilized herein is butadiene.
The first monomer or group of monomers polymer-ized in the presence of the prepolymerized backbone are preferably monovinyl aromatic hydrocarbons. The monovinyl aromatic monomers utilized are generically described by the formula:

Y ~ = C / 7 wherein Yl-Y8 independently are selected from the group consisting of hydrogen, alkyl groups containing ~fo-2494 ~22~i~79c from 1 to 5 carbon atoms, chloro and bromo. Examples of the monovinyl aromatic compounds and substituted monovinyl aromatic compounds that may be used are styrene and other vinyl-substituted aromatic compounds including alkyl-, cycloalkyl-, aryl-, alkaryl-, aralkyl-, alkoxy-, arloxy- and other substituted vinyl aromatic compounds. Examples of such compounds are 3-methylstyrene; 3,5-diethylstyrene and 4-n-propyl-styrene, ~-methylstyrene, ~-methylvinyltoluene, ~-chlorostyrene, vinyltoluene, ~-bromostyrene, chloro-phenyl-ethylenes, dibromophenylethylenes, tetrachloro-phenylethylenes, l-vinylnaphthalene, 2-vinylnaphtha-lene, mixtures thereof and the like. The preferred monovinyl aromatic hydrocarbon used herein is styrene and/or ~-methylstyrene.
The second group of monomers that are poly-merized in the presence of the prepolymeri~ed b~ckbone are acrylonitrile and/or substituted acrylonitrile.
The acrylonitrile and substituted acrylonitrile are described generically by the formula Ylo Yg / C = C - z Yll wherein Y9-Yll independently are selected from the group consisting of hydrogen, alkyl groups containing from 1 to 5 carbon atoms, chloro and bromo and Z is selected from the group consisting of cyano and carb-alkoxy wherein the alkyl group of the carbalkoxy group contains from 1 to about 12 carbon atoms. Examples are acrylonitrile, ~-chloroacrylonitrile, ~-chloroacrylo-nitrile, ~-bromoacrylonitrile and ~-bromoacrylo-nitrile. The preferred acrylic monomer used herein isacrylonitrile.
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The compositions of the present invention are characterized in that the polyalkylene terephthalate resin and the polycarbonate resin are present therein at a weight ratio therebetween of from about 1:1 to about 4:1, preferably from about 1.5:1 to about 3,0:1Ø Further the compositions are characterized in that they contain an impact modifying am~unt, prefer-ably about 5 to 25%, more preferably 10 to 20% of the grart polymer, said percentages being in relation to the total weight of the polyalkylene terephthalate, polycarbonate and graft elastomer.
The compositions of the invention may contain additives and agents such as are know,n in the art to impact certain properties in thermoplastic molding comp~sition~. Among these are plfl~ticizers, heat ~ncl hyclrolytic stabilizers, pigments, fillers, rein-forcement agents and flame retardants of various types.
The materials used in the course of the prepar-ation of the compositions noted below were as follows:
Polyethylene terephthalate - Vituf* 1001A, having an intrinsic viscosity of about 1.04, available commercially from Goodyear Tire and Rubber Company, Ohio.
Polycarbonate - Merlon* M-50 - a bisphenol A
based homopolycarbonate characterized in that its melt index per ASTM D-1238 is about 3.0 to 5.9 gm/10 min., avallable from Mobay Chemical Corporation, Pittsburgh, Pennsylvania.
Graft elastomer Type A - Acryloid* KM 653 a methylmethacrylate styrene graft butadiene having a polybutadiene content of about 70 percent by weight and characterized in that its Tg is about -81C and in that *Trademark Mo-2494 ~3 ~d ~;

~ ~ ~ 5 ~7 -lla-its styrene content is about 20 percent an~ its methyl-methacrylate content is about 10 percent, available from Rohm & Haas Corporation, Philade]phia, Pennsyl-vania .

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Graft Elastomer - Type B - an acrylonitrile styrene graft butadiene characterized in that its Tg is about -86C having a polybutadiene content of about 75 percent by weight and in that its S/AN ratio is about 72/28, available from Bayer AG.
Graft Elastomer - Type C - same as Type B except that its polybutadiene content is about 50 percent by weight.
Other components included in all of the composi-tions and asserted to have no criticality insofar as the surprising impact strength of the compositions of the invention, were added at levels of 0.2 to 0.9 phr (per hundred weight of the polyethylene terephthalate, polycarbonate and graft-elastomer). These were as an antioxidant: an octadecyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate, as a stabilizer: fl tris-[3-ethyl-oxetanyl)-3-methyl]-phosphite carbon black and talc (max. particle size 12 microns).
The extrusion of the compositions of Example 5 and Comparison Example 5 was carried out on a 1 1/2 in.
Hartig extruder 2.75/1 screw, speed 80 rpm, screw set 57, screen pack 20-40-60; temperature profile: rear 270C, middle 265C, front 270~C and die 234C.
The compositions indicated as Examples 1-4 and the Comparison Examples 1-4 were extruded in a twin screw ZSK 53 mm extruder at conditions noted as:
Pellet feeder - set (%): 19 Extruder zone temperature (C, set/read):
Zone 1 - Barrel 260/255 Melt 265 Zone 2 - Barrel 260/265 Melt 255 Mo-2494

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Zone 3 - Barrel 200/202 Melt 292 Zone 4 - Barrel 200/194 Melt 270 Zone 5 - Barrel 240/252 Melt 275 Die Body 245/235 Melt 267 Screw speed (rpm) 85 Torque (%) 66 KWDC (KW) 10.5 Vacuum (mm Hg~ 12 Amps 75 Extruded pellets, after drying at about 110C
for about 16 hours in a hot ~ir circulating oven, w~re injection molded using 4-oæ. Newbury molding machine to prepare test bars. The injection molding conditions were as follows:
Zone set temperature (C): Rear 260 Front 260 Nozzle 254 Mold Surface 70 Melt temperature (C): 260 Cycle time (seconds): Injection 12 Cooling 25 Total Cycle 37 Injection pressure (psi): Primary 850 Secondary 800 The measurements of the Impact strength were carried out in accordance with ASTM D-256. The notched impact strength of gate/end sides were measured using two halves of a 5 inch long bar. The low temperature notched Izod impact strength (at -40C~ was determined after immersing the test bar for one hour in a dry 35 ice/methanol bath at -40C.
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The invention is further illustrated, but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLES
EXAMPLE i Compositions in accordance with the invention were prepared and evaluated. The evalluation entailed a comparison of their properties with those of composi-tions modified by a substantially similar, yet critical-ly different graft elastomer. The comparisons clearly indicate the surprising consequences associated with seemingly minor structural-chemical characteristics of the respective grafts. The processing of the composi-tions below included b]ending of the resinous pellets which were dried at 80-100C overnight and the subsequent addition of the graft elastomers and talc (both dried at 80C). Extrusion was followed by inj ection molding.
Comp. Ex. Comp. Ex.
Polyethylene terephthalate (%) 43.0 43.0 43.0 Polycarbonate, (~) 43.0 43.0 43.0 25 Graft elastomer, (%) Type A - 14.0 Type B 14.0 Type C - - 14.0 Impact strength, Notched Izod 30 (ft.lb/in) gate/end at 23C 13.4/14.612.1/12.2 2.2/3.2 -40C 4.5/4.6 2.4/2.3 1.8/1.8 Compositions in accordance with the invention 35 were prepared and tested as shown below. The prepara-Mo-2494 ~2~ '7~

tion o~ these and of the comparison compositions follows the procedure described above.
Comp. Ex. Comp. Ex.
2 3 _~
Polyethylene terephthalate, % 51.0 51.0 54.0 54.0 Polycarbonate, % 34.0 34.0 36.0 36.0 Graft Elastomer, %
Type A - 15.0 - 10.0 Type B 15.0 - 10.0 Impact strength, Notched I~od ft.lb/in. gate/end at 23C 17.2/17.6 15.9/15.7 17.4/16.8 16.1/14.8 15-40C 11.8/12.6 2.6/2.8 9,0/lO,l~ 2.3/2.8 EXAMPL~S 4-5 Further compositions in accordance with the invention were prepared and set in comparison as noted below. The preparation of these compositions followed the procedure indicated above except that extrusion was carried out using a Hartig extruder (see above~.
Comp. Ex.

Polyethylene 25terephthalate, % 59.5 68.0 68.0 Polycarbonate, % 25.5 17.0 17.0 Graft elastomers, %
Type A - - 15.0 Type B 15.0 15.0 Impact strength, Notched Izod ft.lb./in. gatestend at 23C 21.0/20.618.7/18.7 l9.g/17.8 -40C 14.9/13.2 4.3/3.9 3.9/3.7 ~(o-2494 -16~ 77 ~
Although the invention has been described in detail in the foregoing for the purpose of illustra-tion, it is to be understood that such detail is solely for that purpose and that variations can be made there-in by those skilled in the art without departing fromthe spirit and scope of the invention except as it may be limited by the claims.

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SUPPLEMENT~RY DISCLOSURE
This disclosure and the Principal Disclosure relate to thermoplastic molding composition.
A particularly preferred graft elastomer of the present invention is characterized in that its core is of polybutadiene only and constitutes 70 to 80% by weight of the graft elastomer such that the graft elastomer has a rubbery core to graft phase ratio of 70/30 to 80/20 and the core consists of polybutadiene. The particularly pre-ferred graft elastomer is further characterized in theweight ratio between its grafted monovinyl aromatic hydrocarbon (for instance, styrene) and its grafted acrylonitrile-type compound (for instance, acrylonitrile).
The weight ratio of these is preferably in the range of 74/26 to 66/34. Even more preferably the acrylonitrile-type compound constitutes about 41-50 mol percent relative to the total molar amount of the grafted phase.
As indicated in the Principal Disclosure the polyethylene terephthalate preferably has an intrinsic viscosity of at least 0.4 decilitres per gram.

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Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thermoplastic molding composition comprising:
(i) a polyethylene terephthalate resin charac-terized in that its intrinsic viscosity as measured in a 1% solution of phenol and tetrachloroethane (60:40) at 25°C is at least 0.4 deciliters per gram, (ii) an aromatic polycarbonate resin, and about 5 to 25% relative to the total weight of said (i), (ii) and (iii) of (iii) a graft elastomer having a rubbery core sub-stantially of polybutadiene, said graft elastomer having a polybutadiene content of at least 60% by weight and a graft phase consisting of the polymerization product of:
(a) at least one monovinyl aromatic hydrocarbon of the formula:

wherein Y1-Y8 independently denote a hydrogen, chlorine or bromine atom or a C1-C5 alkyl radical, and (b) at least one acrylonitrile type compound conform-ing to:

wherein Y9-Y11 independently denote a hydrogen, chlorine or bromine atom or a C1-C5 alkyl radical and Z denotes a cyano radical, said composition being further charac-terized in that said (i) relates to said (ii) by weight as 1:1 to 4:1.

2. The composition of claim 1, wherein said mono-vinyl aromatic hydrocarbon is styrene and said acrylo-nitrile type compound is acrylonitrile itself.

3. The thermoplastic molding composition of claim 1 or 2, wherein said polycarbonate resin is derived from bisphenol A.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

4. A thermoplastic molding composition comprising:
(i) a polyethylene terephthalate resin charac-terized in that its intrinsic viscosity as measured in a 1% solution of phenol and tetrachloroethane (60:40) at 25°C is at least 0.4 deciliters per gram, (ii) an aromatic polycarbonate resin, and about 5 to 25% relative to the total weight of said (i), (ii) and (iii) of (iii) a graft elastomer having a rubbery core to graft phase ratio of 70/30 to 80/20 characterized in that its core consists of polybutadiene and that its graft phase consists of the polymerization product of (a) at least one member selected from the group con-sisting of monovinyl aromatic hydrocarbons described by the formula wherein Y1-Y8 independently denote a hydrogen, chlorine or bromine atom or a C1-C5 alkyl radical and (b) at least one acrylonitrile type compound conforming to wherein Y9-Y11 independently denote a hydrogen, chlorine or bromine atom or a C1-C5 alkyl radical and Z denotes a Mo-2494 20 cyano radical, said (a) relating to said (b) by weight as 74/26 to 66/34, said composition being further characterized in that said (i) relates to said (ii) by weight as 1:1 to 4:1.

5. The composition of claim 4, wherein said mono-vinyl aromatic hydrocarbon is styrene and said acrylo-nitrile type compound is acrylonitrile itself.

6. The thermoplastic molding composition of claim 4, wherein said polycarbonate resin is derived from bisphenol A.

7. The thermoplastic molding composition of claim 5, wherein said polycarbonate resin is derived from bisphenol A.

8. The thermoplastic molding composition of claim 4, 5 or 6, wherein said acrylonitrile type compound constitutes about 41-50 mol percent relative to the total amount of said graft phase.

9. The thermoplastic molding composition of claim 7, wherein said acrylonitrile type compound constitutes about 41-50 mol percent relative to the total amount of said graft phase.