EP2838948A1

EP2838948A1 - Nucleating agents for polypropylene and propylene copolymers

Info

Publication number: EP2838948A1
Application number: EP13717273.0A
Authority: EP
Inventors: Piming MA; Yogesh Sheshrao Deshmukh; Carolus Henricus Radjindrenath Maria WILSENS; Sanjay Rastogi
Original assignee: Eindhoven Technical University
Current assignee: Eindhoven Technical University
Priority date: 2012-04-19
Filing date: 2013-04-18
Publication date: 2015-02-25
Also published as: WO2013156565A1

Abstract

Use of a compound or a combination of compounds for crystallization of polypropylene or polypropylene copolymers, characterized in that each of said compounds comprises a core motif with two oxalamide motifs, flanked by two arms, wherein said core motif has the formula: R-NH-C(O)-C(O)-NH-(CH₂)_n-NH-C(O)-C(O)-NH-R', wherein n is between 1 and 10 and the arms R and R' are each independently of one another chosen from: (i) H; (ii) an alkyl group with a total number of carbon atoms between 1 and 20; or (iii) an ester group as e.g. - X-Ester-Y, or - X-Ester- X-Ester-Y, wherein X is a saturated aliphatic hydrocarbon group comprising 1 to 20 carbon atoms, Y is chosen from H or an aliphatic alkyl group with a total number of carbon atoms between 1 and 20 Ester is –C(O)-O- or –O-C(O)-.

Description

NUCLEATING AGENTS FOR POLYPROPYLENE AND PROPYLENE

COPOLYMERS

Description:

The interest in semi-crystalline polymeric materials has increased rapidly in recent decades. Among the polymeric materials, polyolefins are very popular materials. The main factors responsible for the growth in polyolefins consumption are the inherent versatility of these polymers and the ease with which they can be processed. The properties and the morphology of the semi-crystalline polyolefins mainly depend on the molecular structure, processing additives and the processing conditions.

One of the widely used polyolefins is polypropylene (PP). The world-wide market volume of polypropylene is expected to grow from 52 mega tons/year in 2008 to 69.1 megatons/year in 2013. Polypropylene is a thermoplastic polymer which is employed for a large variety of different products: ranging from packaging products, textiles, stationery, plastic parts and reusable containers of various types, laboratory equipment to automotive components. PP consists basically of a sequence of propylene monomers, where a methylene group is present as side group on every other carbon atom in the backbone chain. PP is classified into three different subgroups as atactic PP (aPP), isotactic PP (iPP) and syndiotactic PP (sPP). In aPP, the side groups are randomly distributed, which results in amorphous, rubbery materials. In contrast, iPP has side groups consistently on one side, offering long range order for crystallization. While in the case of sPP, the side groups are distributed in alternating fashion along the backbone. Isotactic polypropylene is the isoform mainly used commercially. Main drawbacks in the use of PP are its low nucleation density and slow crystallization rate. To improve these disadvantages nucleating agents are used for the crystallization of polypropylene.

Nucleating agents for polypropylene are known.

Widely used as nucleating agents for PP are sorbitol compounds, as e.g. dibenzylidene sorbitol which is disclosed in US40161 18.

US2010317779 teaches a composition of scratch resistant polypropylene which is produced with a nucleating agent selected from the group consisting of sodium benzoate, 2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate, zinc glycerolate, calcium salt of 1 ,2-dicarboxylic acid cyclohexane and sodium salt of 1 ,2- dicarboxylic acid norbornane. Also US2010010168 and WO201 1 131 123 describe the use of carboxylate compounds as nucleating agents, the latter in combination with a phosphate-type nucleating agent.

US201 1 13101330 discloses a polypropylene resin composition comprising an polypropylene polyethylene copolymer and an amide compound as nucleating agent. In the nucleating agent the amide groups are substituents of an aromatic ring or in the form of a propane tricarboxylic acid triamide.

EP0557721 and EP1431335 describe bisamide compounds for the crystallization of polypropylene.

The combination of nucleation efficiency, decrease in crystallization half-time, and desired transparency of the product in the presence of the nucleating agents is not optimal in prior art. The aim of present invention is to overcome at least in part the disadvantages that lie in the use of known nucleating agents and to provide alternative nucleating agents for polypropylene and polypropylene copolymers.

To achieve this, the present invention suggests to use a class of compounds as nucleating agents for polypropylene and polypropylene copolymers, which compounds have high nucleation efficiency and a melting temperature which can be adjusted to the melting temperature of the specific polypropylene or polypropylene copolymers. Also, due to the use of the nucleating agents the half- time of crystallization of the polymer is decreased. The nucleating agents of present invention allow for a high onset crystallization temperature and high degree of crystallinity. Additionally, the inventive use of the nucleating agents results in good transparency and structural order of the polypropylene or polypropylene copolymers.

Another objective of this invention is to provide a process for crystallization of polypropylene or polypropylene copolymers wherein the nucleating agent has high nucleation efficiency.

Furthermore, a composition of polypropylene or polypropylene copolymer and nucleating agents with high nucleation efficiency are provided and films, moldings, composite materials, extrusion- or injection-molded products or elongated products comprising the composition.

Throughout this description the terms 'nucleating agent' and 'compound' are used interchangeably.

These tasks are solved by using a compound or a combination of compounds for crystallization of polypropylene or polypropylene copolymers, characterized in that each of said compounds comprises a core motif with two oxalamide motifs, flanked by two arms, wherein said core motif has the formula:

R-NH-C(O)-C(O)-NH-(CH₂)_n-NH-C(O)-C(O)-NH-R', wherein n is between 1 and 10 and the arms R and R' are each independently of one another chosen from:

(i) H; (ii) an alkyl group with a total number of carbon atoms between 1 and 20; or

(iii) one of the following esters:

- X-Ester-Y,

- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-Y, or

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-X-Ester-Y;

wherein X is a saturated aliphatic hydrocarbon group comprising 1 to 20 carbon atoms, Y is chosen from H or an alkyl group with a total number of carbon atoms between 1 and 20 and Ester is -C(O)-O- or -O-C(O)-.

Oxalamide and bisoxalamide compounds are known (Deshmukh S. et al., PMSE Preprints, American Chemical Society, 201 1 , vol. 104, p. 343-345) However, it is surprising that these compounds present such efficient nucleating agents for polypropylene and polypropylene copolymers. EP0421377 shows that unsymmetric bisoxalamides substituted with aromatic moieties in the center or in the side arms are used as nucleating agents for polyethylene terephthalates. However, polypropylene includes no aromatic or cyclic moieties.

The flexible side arms of the nucleating agents and the flexible bridging motifs between the oxalamides, disclosed in this application, will enhance the aggregation process prior to crystallization of the polypropylene or polypropylene copolymer. The similarity of the chemical structure of the side arms with the chemical structure of polypropylene will ensure a proper dissolution and a homogeneous distribution in the polymer melt.

In one embodiment at least one of the side arms R and R' is chosen from an alkyl group with a total carbon number between 2 and 20, preferably with a total carbon number between 4 and 10 and more preferably with a total carbon number between 6 and 8.

In another embodiment the hydrogen atoms on the saturated aliphatic

hydrocarbon group and/or on the alkyl side arms R or R' are substituted by methyl, ethyl or alkyl groups of up to 8 carbon atoms, where the total number of all carbon atoms of the saturated aliphatic hydrocarbon group or the alkyl group is not higher than 20. This means that in this embodiment at least one of the arms R or R' comprises a branched alkyl group and/or a branched saturated aliphatic

hydrocarbon group.

An ester is a group containing a carbonyl connected to an oxygen atom (-C(O)-O-) or an oxygen atom connected to a carbonyl group (-O-C(O)-).

The saturated aliphatic hydrocarbon group (referred to as X) comprising 1 to 20 carbon atoms is part of an alkane chain and only consists of carbon and hydrogen atoms. All carbons are bound to each other by single carbon bonds. X includes unbranched carbon chains and branched carbon chains, i.e. isomers where the total number of carbon atoms is limited to 20.

The saturated aliphatic hydrocarbon group is bound to the other moieties of the nucleating agent by two bonds.

Examples of the aliphatic hydrocarbon group are: -CH₂-CH₂-CH₂- or -CH₂(CH₃)- CH₂-.

For example, the saturated aliphatic hydrocarbon group is bound to a methyl group or H (i.e. Y) on one side and to an ester group or the bisoxalamide motif, i.e. the core of the nucleating agent on the other side.

An alkyl is an aliphatic moiety with a total number of carbon atoms between 1 and 20, i.e. a functional group comprising only carbon and hydrogen atoms derived from an alkane by removing one hydrogen atom. This definition includes

unbranched carbon chains and branched carbon chains, i.e. isomers.

Examples are: methyl, ethyl, propyl or isopropyl. For example one compound according to the invention has the following structural formula:

NA2: JY ,N -(ethane- l,2-diyl)bis(N -hexyloxalamide)

In another embodiment the structural formula can be:

NA3: N^N'-iethane-l ,2-diyl)bis(N²-decyloxalamide)

Or:

NA4: Ν',Ν' -(ethane- 1 ,2-d j;i,y,n 1 )ub;is_na(.V;2^" - exadec loxalamide)

NA5: N ,N - exane-l,6- y siV - exyoxaam e

The following compounds are also nucleating agents according to present invention. These non-limiting examples include compounds with symmetric arms (R is identical to R') , as e.g.:

N¹ ,N^] -{ hexane- 1 ,6-diy I )bis( Λ ^: -( undecaii-6-y! (oxalamide)

N^N¹ '-(hexane- l,6-diyl)bis(N²-(4,6-dimethylheptan-2-yl)oxalamide)

dineopentyl 2, 17-dimethyl-4,5, 14, 15-tetraoxo-3 ,6, 13, 16-tetraazaoctadecane- 1 , 1 8-dioate and nucleating agents with asymmetric flanking arms (R and R' are different), as e.g.:

2,5-dimethyl-4,7,8,15,16-pentaoxo-3-oxa-6,9,14,17-tetraazahenicosan-l-oic acid

The core motif comprises two oxalamide motifs. Amide motifs are hydrogen bonding motifs. They are the driving force for crystallization of the polymer. Because multiple amide motifs are present in the compound the hydrogen bonding is very strong. The hydrogen bonding leads to self-assembly of compound molecules, which form long needle-like structures that act as nucleating agent for the polymer.

In the present invention the amide motifs are connected by alkyl moieties (part of an alkane chain, -CH₂-), which can differ in length between a methyl moiety (n=1 ) and a decanyl moiety (n=10). The different length of the alkyl moiety influences the peak melting and crystallization temperature of the compound in such a manner that a longer alkyl chain or spacer decreases the melting temperature while a shorter spacer increases the melting temperature (Table 1 ). Compare e.g. NA2 and NA5 in table 1 . The length of the aliphatic spacer can be used as a tool to design the optimal compound for a specific polymer matrix in terms of its solubility and melting temperature. Control of the melting point is useful to use the compound or a combination of compounds as efficient nucleating agent with polypropylene or different polypropylene copolymers which have a range of melting temperatures. The nucleating agents according to present invention have peak melting temperatures ranging from 150 to 300°C. For example N¹ ,N¹ -(hexane-1 ,6- diyl)bis(N²-phenyloxalamide) has a peak melting temperature of 272°C.

Table 1 : Melting and crystallization temperature of nucleating agents

T_m - peak melting temperature of the nucleating agent

T_C ^NA - peak crystallization temperature of the nucleating agent

The tunable melting temperature of the compounds is an advantage of the present invention over nucleating agents known previously. Also the high melting temperature of the compounds is an advantage over previously known nucleating agents. The high melting temperature that arises due to strong hydrogen bonding results in a very high nudeation efficiency of the nucleating agent. It also allows for the use of the compound or a combination of compounds as nudeation agent for polymers with a tailored melting temperature. For example, 100% iPP has an approximate peak melting temperature of 166°C, while a 93% propylene / 7% ethylene copolymer has a peak melting temperature of 140°C approximately. The peak melting temperature (or dissolution temperature) of the nucleating agent decreases when mixed with the polymer. The decrease in the peak melting temperature (T_m) and peak crystallization temperature (T_c) of the nucleating agent when mixed with polypropylene shows its good miscibility in the polymer melt (Table 2).

Table 2: Crystallization of NA2 in a PP matrix.

The arms R and R' can be chosen in a way to improve the miscibility with the polymer. A good miscibility of the nucleating agent with the polymer causes a homogenous distribution of the nucleating agent in the polymer matrix and leads to better crystallization. This is obtained by designing the arms to be similar to the molecular configuration of the polymer. When R, R' and the molecular configuration of the polymer to be crystallized are similar, the crystal structure of the compound suppresses the nucleation barrier and increases the nucleation efficiency of the polymer, thus increasing the crystallization rate.

For the crystallization of polypropylene and polypropylene copolymers the flanking arms are independently of each other chosen from:

(i) H;

(ii) an alkyl group with a total number of carbon atoms between 1 and 20; or

(iii) one of the following esters:

- X-Ester-Y,

- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester-Y, - X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-Y, or

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-X-Ester-Y;

In this way symmetric and asymmetric nucleating agents can be produced.

The nucleating agents according to present invention can be used to crystallize polypropylene polymer and polypropylene copolymers. For the purpose of this invention polypropylene includes isotactic, syndiotactic and atactic polypropylene, where the tacticity can vary from approximately 60 to 100% in the case of isotactic and syndiotactic polypropylenes.

Polypropylene copolymers for the purpose of this invention include polypropylene- alpha-olefin copolymers and poly(propylene-styrene) copolymers. Examples for suitable alpha-olefins include but are not limited to polyethylene (PE), polybutylene, and poly(4-methyl-1 -pentene). The polypropylene copolymers include polypropylene block copolymers and polypropylene random copolymers. The polypropylene copolymers comprise at least 60% propylene units. A preferred polypropylene copolymer is a propylene-ethylene copolymer, where e.g. the amount of ethylene monomers varies between 1 and 10 mole% based on the total amounts of monomers which are used to produce the polymer, preferably between 2 and 5 mole%.

In one embodiment according to this invention one compound according to the invention can be used to crystallize polypropylene and polypropylene copolymers. In another embodiment a combination of compounds according to present invention is used to crystallize polypropylene or polypropylene copolymers. For the crystallization the compound or the combination of compounds are applied at a concentration of 0.05-2wt%, preferably 0.1 -1wt%, more preferably 0.2-0.5wt% based on the weight of the polypropylene or propylene copolymer.

If a combination of compounds is used to crystallize polypropylene or polypropylene copolymers, said amounts refer to the combined amount of the different compounds. This means that the total amount of nucleating agent added to the polymer can either consists of one nucleating agent or a combination of different nucleating agents according to this invention. If a combination of nucleating agents is used, the total amount of nucleating agents is the same as if one nucleating agent is used. The amount is always based on the weight of the polymer or copolymer. For example, 0.05wt% of nucleating agent A and 0.05wt% of nucleating agent B result in an amount of 0.1 wt% nucleating agent based on the weight of the polymer.

The relative amount of each compound of such a combination of compounds can vary depending on the polymer, copolymer or polymer mixture which is to be crystallized.

In another embodiment the invention relates to a process for crystallization of polypropylene or polypropylene copolymer, comprising the steps of:

(a) mixing polypropylene or a polypropylene copolymer with a compound or a combination of compounds at a first temperature, ranging from 10°C to 140°C above the peak melting temperature of the polymer; and

(b) cooling the polymer at a second temperature, ranging from the first

temperature to 20°C, characterized in that each of said compounds comprises a core motif with two oxalamide motifs, flanked by two arms, wherein said core motif has the formula:

(i) H;

(ii) an alkyl group with a total number of carbon atoms between 1 and 20; or

(iii) one of the following esters:

- X-Ester-Y, - X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-Y, or

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-X-Ester-Y;

When studying the morphology of the nucleating agents according to this invention in the polymer matrix with optical microscopy, a fine needle-like morphology of the nucleating agents can be observed and the polymer starts crystallizing from the surface of the nucleating agent. The presence of the fine needle-like morphology of the nucleating agent enhances the nucleation efficiency of the polymer in comparison with a polymer without nucleating agents. The dimensions of the needle-like crystals vary with the crystallization conditions and the chosen combinations of the nucleating agents. With smaller crystal size the surface area of the nucleation site is increased which improves the crystallization and nucleation efficiency.

In one embodiment the nucleating agents of present invention have a crystal size in the polymer matrix of up to 50 micrometer (μιτι). Preferably the crystal size is below several hundreds of nanometer (nm), e.g. between 10 and 750 nm, more preferably between 50 and 500 nm, even more preferably between 100 and 250 nm. The crystal size of the nucleating agent in the polymer matrix can be determined by optical microscopy or electron microscopy or atomic force microscopy.

The nucleating agents according to the invention show high nucleation efficiencies. The nucleation efficiency (NE) is defined as the increase of the crystallization temperature of the polymer with the nucleating agent compared to the crystallization temperature without nucleating agent. This is calculated by using equation 1 :

NE = (T_c - T_cl )/(r_c2max - T_el ) x 100% , where T_ci and T_C2max are the peak crystallization temperatures of the non- nucleated and self-nucleated polymer, respectively. T_c is the peak crystallization temperature of the polymer with the nucleating agents.

Polypropylene and polypropylene copolymers crystallize inefficiently without a nucleating agent in industrial processing. The material which can be obtained without nucleating agent is of lower crystallinity and has a lower dimensional stability.

However, with the here described nucleating agents or combinations thereof the onset temperature for crystallization of the polymer is increased. The here described nucleating agents or combinations thereof increase the onset crystallization temperature by at least 5°C, preferably by at least 10°C, more preferably by at least 15°C, or by at least 20°C compared to the polymer or copolymer without any nucleating agent. The specific temperature depends on the specific compound or combination of compounds according to this invention, the amount of nucleating agent and the polymer or copolymer. A higher onset temperature is better for the produced plastics because the mechanical properties of the material are better, the production time is shorter because less cooling has to take place and no or less shrinkage of the crystallized polymer occurs. The high nucleation efficiency provides the desired dimension stability. Thus, the high onset crystallization temperature of the polymer or copolymer in the presence of the nucleating agents of present invention enables easier processibilty and a higher dimension stability of the polymer product. Additionally, PP or PP copolymers crystallized with nucleating agents according to this invention or a combination of those have a good transparency. With the nucleating agents according to this invention the temperature at which the polymer and the compound or combination of compounds are mixed ranges between 10°C and 140°C, preferably between 20 and 120°C, more preferably between 40°C and 120°C above the peak melting temperature of the polymer.

The temperature at which the polymer and the compound or combination of compounds are cooled ranges from about 140°C above the peak melting temperature of the polymer to 20°C, preferably from 120°C above the peak melting temperature of the polymer to 20°C. In one embodiment the polymer and the compound or combination of compounds are cooled at room temperature.

As pointed out before a high crystallization temperature is beneficial for the polymer product and its production.

The cooling occurs at a rate ranging between 1 °C/min and 500°C/min, preferably between 10°C/min and 300°C/min, more preferably between 20°C/min and 100°C /min.

With an increasing cooling rate the nucleation efficiency becomes more evident and it reduces production time.

In another embodiment the invention relates to a composition comprising polypropylene or polypropylene copolymer, and a compound or a combination of compounds, characterized in that each of said compounds comprises a core motif with two oxalamide motifs, flanked by two arms, wherein said core motif has the formula:

(i) H;

(ii) an alkyl group with a total number of carbon atoms between 1 and 20; or

(iii) one of the following esters:

- X-Ester-Y, - X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-Y, or

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-X-Ester-Y;

The composition comprises 0.05-2wt%, preferably 0.1 -1wt%, more preferably 0.2- 0.5wt% of the compound or a combination of compounds based on the weight of the polypropylene or propylene copolymer.

In one embodiment films, moldings, composite materials, injection- or extrusion- molded products or elongated products comprise a composition according to this invention. Elongated products include fibers, as e.g. staple fiber and short fiber.

It is also possible to crystallize a polymer mixture of polypropylene homopolymer and polypropylene copolymer with a compound or combination of compounds according to this invention. The resulting composition can therefore comprise polypropylene, polypropylene copolymer or a polymer mixture together with one compound or a combination of compounds according to this invention.

Such compositions can be used to produce films, moldings, composite materials, injection- or extrusion molded products or elongated products.

More specifically, any of said compositions can be used in plastic carrier bags, bottles, food packaging products and textiles. Especially advantageous is the use of a composition according to the invention for bottles and food packaging products because many of the nucleating agents according to present invention are considered non-toxic. The following examples describe the invention in more detail but by no means limit the scope of the invention.

Synthesis of compound & methods for measuring the characteristics of compound and compound-polymer composition

1 . Synthesis of compounds

As an example the synthesis of NA1 and NA2 is described:

a) Synthesis of NA1 (N¹,N¹ -(hexane-1 ,6-diyl)bis(N²-phenyloxalamide))

Ethyl oxanilate (5 g, 25.8 mmol) was dissolved in 200 ml of chloroform. 1 ,6- hexamethylenediamine (1 .5 g, 12.9 mmol) was added and the mixture was left to stir under reflux for 48 hours. The formed precipitate was filtered and washed successively with chloroform and diethyl ether before drying in vacuo overnight (80 °C). The product was obtained as a white powder, showed a (1 ^st) melting point of 273°C and a crystallization point at 252°C. The compound is thermally stable up to 280 °C. Nuclear magnetic resonance spectroscopy (¹H-NMR) analysis of NA1 gave the following result: (Yield 4,78 g, 90%). ¹ H-NMR(TFA-d) δ (ppm): 7.46 (d, ArH, 4H), 7.35 (t, ArH, 4H), 7.25 (t, ArH, 2H), 3.45 (t, NH-CH₂, 4H), 1 .70 (m, NH- CH2-CH2, 4H ), 1 .45 (m, NH-CH₂-CH₂-CH₂, 4H). b) Synthesis of NA2 (N¹,N^{1 '}-(ethane-1 ,2-diyl)bis(N²-hexyloxalamide))

Diethyl 2,2'-(ethane-1 ,2-diylbis(azanediyl))bis(2-oxoacetate) (5 g, 19.2 mmol) and hexylamine (3.91 g, 38.4 mmol) were dissolved in 200 ml chloroform. The mixture was refluxed for 48 hours and the precipitate was filtered and washed with chloroform and diethyl ether before drying in vacuo at 80 °C overnight (yield 6.55 g, 92%). The obtained powder shows a melting point of 287°C and re-crystallizes at 278°C. The product starts to degrade around 280°C with its onset point at 300°C. ¹H-NMR spectroscopy of NA2 gave the following result: ¹ H-NMR(TFA-d) δ (ppm): 3.66 (s, NH-CH₂-CH₂-NH, 4H), 3.35 (t, NH-CH₂-CH₂-CH₂, 4H), 1 .59 (m, NH-CH₂-CH₂-CH₂, 4H), 1 .28 (b, CH₂, 12H), 0.83 (t, CH₃, 6H). 2. Melt mixing

Melt mixing of the nucleating agent and the polymer was performed using a mini- extruder with sample residence time of 5 min after complete feeding. In the examples isotactic polypropylene (Sabic, grade 1531 P) or a propylene-ethylene copolymer comprising 5 mole% (Dow, Versify 2000®) or 9 mole% (Dow, Versify 2200®) of ethylene monomers and 95 mole% or 91 mole% of propylene monomers respectively was used as polymer. All samples were prepared using 0- 1 % of a nucleating agent by weight of the polymer. The samples were processed at 230 or 280°C.

3. Differential Scanning Calorimetry (DSC)

Melting and crystallization of polymers without and with nucleating agent was investigated using DSC (TA Q1000 instrument) under nitrogen atmosphere. The heating rate was always 20°C/min and cooling rates of all samples were 100°C/min and/or 10°C/min (as indicated) with 3 min of isothermal condition at limiting temperatures. The samples were heated up to 230°C or 280°C (as indicated) and cooled down to 20°C. Isothermal crystallization measurements were performed on the polymer without and with nucleating agent at 130°C for an isothermal time of 1 hr.

The onset melting temperature is defined as the start of the endothermic process, whereas the peak melting temperature or peak melting point is defined as the peak of the endothermic process recorded by DSC. The onset crystallization temperature is defined as the start of the exothermic process, whereas the peak crystallization temperature is defined as the peak of the exothermic process recorded by DSC.

4. Optical Microscopy

Crystallization measurements were conducted on a Zeiss Axioplan 2 Imaging optical microscopy under crossed polarizers with a CD achorplan objective (Zoom). A THMS 600 heating stage connected to a Linkam TMS 94 control unit was mounted on the optical microscope. Samples were heated to above the melting temperature of the polymer and cooled at a specific cooling rate under nitrogen atmosphere.

Abbreviations and symbols:

NA1 : N¹ ,N¹ -(hexane-1 ,6-diyl)bis(N²-phenyloxalamide)

NA2 : N¹ ,N^{1 '}-(ethane-1 ,2-diyl)bis(N²-hexyloxalamide)

NA3 : N¹ ,N^{1 '}-(ethane-1 ,2-diyl)bis(N²-decyloxalamide)

NA4 : N¹ ,N¹'-(ethane-1 ,2-diyl)bis(N²-hexadecyloxalamide)

NA5 : N¹ ,N¹'-(hexane-1 ,6-diyl)bis(N²-hexyloxalamide)

NE : Nucleation efficiency (according to equation 1 )

T_m : Peak melting temperature of the polymer, nucleating agent or polymer in the presence of the nucleating agent (cf. tables 3 and 4)

T_C /T_C ^N : Peak crystallization temperature of the polymer in the presence of the nucleating agent (T_C ^N) or of the pristine polymer (T_c)

Tonset : Onset of crystallization temperature of the polymer in the presence of the nucleating agent or of the pristine polymer

Xc Percentage crystallinity of the polymer

to.5 Half time of isothermal crystallization of the polymer

AH_m Enthalpy of melting of the polymer

Enthalpy of crystallization of the polymer

Tel peak crystallization temperature of the non-nucleated polymer

Tc2max peak crystallization temperature of the self-nucleated polymer

Example 1

Polypropylene and a varying amount of the nucleating agents NA1 , NA2, NA3, NA4, NA5 or sorbitol (DMDBS) were melt-mixed and processed at 230 or 280°C. The cooling rate was set to 10 or 100°C/min. A cooling rate of 100°C/min corresponds to conditions similar to those used in industrial production. The nucleating efficiencies of the nucleating agents are shown in Table 3. The polymer without the nucleating agent crystallizes at 1 13 and 105°C corresponding to the cooling rate of 10 and 100 °C/min, respectively, whereas the polymer in the presence of nucleating agents can crystallize at a range of temperatures (Table 3). The nucleating agent NA2 at a concentration of 0.4 and 1 .0wt% showed a very good nudeation efficiency for the polymer matrix at faster (100°C/min) and as well at slower (10°C/min) cooling rates.

Table 3: Nudeation efficiency of NA for PP obtained from DSC measurements.

Sample Tc Tonset Xc T_m NE^* Processing Cooling

(°C) (°C) (%) (°C) (%) temperature rate

(°C) (°C/min)

NA1 251 272 10

NA2 282 289 10

NA3 258 264 10

NA4 244 248 10

NA5 221 225 10

PP 1 13 1 16 43 166 0 230 10

PP + 1 .0 wt% NA1 1 17 128 42 164 16 230 10

PP + 0.4 wt% NA2 120 124 43 163 29 230 10

PP + 1 .0 wt% NA2 123 127 44 164 41 230 10

PP + 1 .0 wt% NA3 120 123 44 163 27 230 10

PP + 0.5 wt% NA4 1 16 1 18 45 162 12 230 10

PP + 1 .0 wt% NA4 1 15 1 17 44 161 8 230 10

PP + 0.5 wt% NA5 1 19 124 44 165 25 230 10

PP + 1 .0 wt% NA5 121 125 43 162 33 230 10

PP 105 109 43 166 0 230 100

PP + 1 .0 wt% NA1 1 16 121 44 164 40 230 100

PP + 0.4 wt% NA2 1 12 1 17 44 159 26 230 100

PP + 1 .0 wt% NA2 1 15 1 19 45 164 37 230 100

PP + 1 .0 wt% NA3 1 12 1 15 45 163 26 230 100 PP + 0.5 wt% NA4 1 16 1 18 43 162 40 230 100

PP + 1 .0 wt% NA4 1 1 1 1 13 44 161 22 230 100

PP + 0.5 wt% NA5 1 1 1 1 16 44 160 22 230 100

PP + 1 .0 wt% NA5 1 12 1 17 44 160 26 230 100

PP + 0.2 wt% NA2 1 13 1 17 44 159 29 280 100

PP + 0.2 wt%

DMDBS 1 13 1 15 44 159 29 280 100

PP 1 12 1 15 43 159 0 280 10

PP + 0.2 wt% NA2 1 19 123 46 159 25 280 10

PP + 0.5 wt% NA2 122 126 43 161 49 280 10

PP + 1 .0 wt% NA2 122 126 48 159 49 280 10

PP + 0.2 wt%

DMDBS 1 17 1 18 44 159 16 280 10

^*: according to the above definition, i.e. equation 1 . T_C2max is 137.4°C (referred from Journal of Thermal Analysis, 1994, 42, 721 -731 ) and 132.3^°C (measured by DSC at a cooling rate of 100 °C/min from a partial melt state) for the cooling rate of 10^°C/min and 100°C/min, respectively.

To investigate how the nucleating agents influence crystallization time, the half time of crystallization was measured by DSC.

In the presence of the nucleating agent, the isothermal crystallization results, as shown in Table 4, clearly demonstrate that the half time of crystallization (t_{0 5}) decreased dramatically after using nucleating agents, at the same time an increase in the melt enthalpy of the polymer is evident. Table 4: Isothermal crystallization results of PP with varying nucleating agents obtained from DSC measurements.

Example 2

For a comparison, the same process as for example 1 was carried out with different nucleating agents known from the prior art to compare the nucleating agents of present invention and those already known. N'¹, N'⁹ diheptanoylnonane- dihydrazide (DHNHZ) and N¹,N⁶-diphenyladipamide (DPAD) were tested. DPAD is a bisamide compound with an aliphatic linker between the amide groups and benzol rings as side arms. DHNHZ is a dihydrazide, i.e. the order of the amide groups is inverted when compared to an oxalamide residue. The results of the known nucleating agents and nucleating agents according to this invention are listed in Table 5.

Table 5: Crystallization of P with various nucleating agents.

Sample Tc Tonset Xc T_m NE^* Processing Cooling

(°C) (°C) (%) (°C) (%) temperature rate

(°C) (°C/min)

PP 105 1 14 44 161 0 230 100

PP + 0.5wt% 151/

DPAD 1 1 1 1 18 37 162^** 22 230 100

PP + 0.5wt%

DHNHZ 108 1 16 45 160 1 1 230 100 PP + 0.4 wt% NA2 1 12 1 17 44 159 26 230 100

PP + 1 .0 wt% NA2 1 15 1 19 45 164 37 230 100

PP + 0.5 wt% NA4 1 16 1 18 43 162 40 230 100

^*: according to the above definition, i.e. equation 1 . T_C2max is 137.4°C (referred from Journal of Thermal Analysis, 1994, 42, 721 -731 ) and 132.3^°C (measured by DSC at a cooling rate of 100 °C/min from a partial melt state) for the cooling rate of 100°C/min, respectively.

*^*: double melting peaks observed

The results show that the nucleating agents of the prior art result in a lower nucleating efficiency and also lower crystallinity compared to the nucleation agents of present invention.

The bisamide compound known from EP0557721 and EP1431335 (as e.g. DPAD) and the compounds described in EP0421377 comprise amide motifs and cyclic or aromatic groups. In contrast, the nucleating agents of present invention do not comprise cyclic or aromatic groups.

Without to be bound by any theory one can speculate that the aromatic or cyclic groups of the nucleating agents of the prior art are likely to perturb the aggregation of the amide motifs due to the sterical hindrance of the cyclic or aromatic motifs. This could result in a lower nucleation efficiency when used as nucleating agents for polypropylene or polypropylene copolymers. EP0421377 describes the use of such nucleating agents to crystallize polyethylene terephthalates.

Example 3

The nucleating agents of present invention are also suited for the crystallization of polypropylene copolymers. A propylene-ethylene copolymer (PP-co-PE) comprising 5 mole% (Dow, Versify 2000®) or 9 mole% (Dow, Versify 2200®) of ethylene monomers and 95 mole% or 91 mole% of propylene monomers respectively was used as polymer for the crystallization with NA2. No nucleating efficiency can be determined because the maximum crystallinity for the specific mole% of the copolymer will be dependent on the polymerization conditions like catalyst, temperature etc. However, the increase of the T_c and T_onSet in presence of the nucleating agent indicate that the nucleating agent according to this invention enhances the crystallization temperature of copolymers and promotes crystallization.

Table 6: Crystallization of polypropylene copolymers

Sample Processing Cooling

Tc Tonset temperature rate

(°C) (°C) (°C) (°C/min)

PP-co-PE (5%) 74 78 230 10

PP-co-PE (5%) + 0.5

wt% NA2 79 83 230 10

PP-co-PE (5%) 67 71 230 100

PP-co-PE (5%) + 0.5

wt% NA2 70 75 230 100

Claims

Nucleating agents for polypropylene and polypropylene copolymers

Claims:

1 ) Use of a compound or a combination of compounds for crystallization of polypropylene or polypropylene copolymers, characterized in that each of said compounds comprises a core motif with two oxalamide motifs, flanked by two arms, wherein said core motif has the formula:

(i) H;

(ii) an alkyl group with a total number of carbon atoms between 1 and 20; or

(iii) one of the following esters:

- X-Ester-Y,

- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-Y, or

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-X-Ester-Y; wherein X is a saturated aliphatic hydrocarbon group comprising 1 to 20 carbon atoms, Y is chosen from H or analkyl group with a total number of carbon atoms between 1 and 20 and Ester is -C(O)-O- or -O-C(O)-.

2) The use of the compound or the combination of compounds according to claim 1 wherein at least one of the side arms R and R' is chosen from an alkyl group with a total carbon number between 2 and 20, preferably with a total carbon number between 4 and 10 and more preferably with a total carbon number between 6 and 8.

3) The use of the compound or the combination of compounds according to claim 1 or 2 wherein each of the compounds has a peak melting temperature ranging between 150 and 300°C.

4) The use of the compound or the combination of compounds according to any one of claims 1 -3 wherein the compound or the combination of compounds are applied at a concentration of 0.05-2wt%, preferably 0.1 -1wt%, more preferably 0.2- 0.5wt% based on the weight of the polypropylene or propylene copolymer.

5) A process for crystallization of polypropylene or polypropylene copolymers, comprising the steps of:

(b) cooling the polymer at a second temperature, ranging from the first

(iii) one of the following esters:

- X-Ester-Y,

- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-Y, or

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-X-Ester-Y;

6) The process according to claim 5, wherein each of the compounds has a peak melting temperature ranging between 150°C and 300°C.

7) The process according to claim 5 or 6, wherein the compound or the combination of compounds are applied at a concentration of 0.05-2wt%, preferably 0.1 -1wt%, more preferably 0.2-0.5wt% based on the weight of the polypropylene or propylene copolymer.

8) The process according to any one of claims 5 to 7, wherein the first temperature ranges between 10°C and 140°C, preferably between 20°C and 120°C, more preferably between 40°C and 120°C above the peak melting temperature of the polymer.

9) The process according to any one of claims 5 to 8, wherein the second temperature ranges from 140°C above the peak melting temperature of the polymer to 20°C, preferably from 120°C above the peak melting temperature of the polymer to 20°C. 10) The process according to any one of claims 5 to 9, wherein the cooling occurs at a rate ranging between 1 °C /min and 500°C /min, preferably between 10°C /min and 300°C /min, more preferably between 20°C /min and 100°C /min.

1 1 ) A composition comprising polypropylene or polypropylene copolymer, and a compound or a combination of compounds, characterized in that each of said compounds comprises a core motif with two oxalamide motifs, flanked by two arms, wherein said core motif has the formula:

(i) H;

(ii) an alkyl group with a total number of carbon atoms between 1 and 20; or

(iii) one of the following esters:

- X-Ester-Y,

- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-Y,

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-Y, or

- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester- X-Ester-X-Ester-X-Ester-Y;

12) The composition according to claim 1 1 , wherein the compound or a combination of compounds is applied at a concentration of 0.05-2wt%, preferably 0.1 -1wt%, more preferably 0.2-0.5wt% based on the weight of the polymer. 13) A film, molding, composite material, extrusion- or injection-molded product or elongated product comprising the composition according to claim 1 1 or 12.