WO2000069956A1

WO2000069956A1 - Hydrogenated vinyl aromatic polymer compositions containing stabilizers

Info

Publication number: WO2000069956A1
Application number: PCT/US2000/010610
Authority: WO
Inventors: John T. Blaha; Gary D. Parsons; Jerry L. Hahnfeld
Original assignee: The Dow Chemical Company
Priority date: 1999-05-19
Filing date: 2000-04-20
Publication date: 2000-11-23
Also published as: AU4473500A; JP2003517502A

Abstract

The present invention is directed to a composition comprising: a) a hydrogenated vinyl aromatic homopolymer or copolymer, and b) a light stabilizer mixture comprising: 1) a hindered amine, and 2) an ultraviolet (UV) light absorber.

Description

HYDROGENATED VINYL AROMATIC POLYMER COMPOSITIONS CONTAINING STABILIZERS

This invention relates to hydrogenated vinyl aromatic polymer compositions. This invention particularly relates to ultra-violet (UV) stabilized hydrogenated vinyl aromatic polymer compositions.

Hydrogenated vinyl aromatic polymers such as polyvinylcyclohexane (PVCH) are generally stable when exposed to UV irradiation. However, there are situations wherein the inherent stability of the polymer is inadequate. These situations include prolonged exposure to sunlight, artificial light or exposure to light at elevated temperatures.

Metal halide light sources are currently used in many commercial light sources.

When exposed to metal halide light sources and the heat generated therefrom, both polycarbonate and PVCH perform unfavorably, having unacceptable yellowness index values. Therefore, there remains a need for a transparent, heat resistant polymer compositions which also possesses acceptable yellowness index values upon prolonged exposure to metal halide light sources.

In one aspect, the present invention is a polymer composition comprising:

a) a hydrogenated vinyl aromatic homopolymer or copolymer, and

b) a light stabilizer mixture comprising:

1 ) a hindered amine, and

2) a ultraviolet (UV) light absorber.

In another aspect, the present invention is an article produced from such a polymer composition.

The composition of the present invention has an excellent yellowness index when exposed to metal halide light for extended periods of time.

In one embodiment, the present invention is a polymer composition comprising a hydrogenated vinyl aromatic polymer, that is, a homopolymer or copolymer, and a light stabilizer composition. The hydrogenated vinyl aromatic polymer used in the present invention includes any vinyl aromatic polymer which has been hydrogenated to a level of at least 60 percent aromatic hydrogenation, generally at least 80 percent, preferably at least 90 percent, more preferably at least 95 percent and most preferably at least 98 percent. Level of hydrogenation is determined by UV-Vis Spectrophotometry. Methods of hydrogenating aromatic polymers are well known in the art such as that described in U.S. 5,612,422 by Hahn and Hucul, wherein aromatic polymers are hydrogenated by contacting an aromatic polymer with a hydrogenating agent in the presence of a silica supported metal hydrogenation catalyst having a narrow pore size distribution and large pores.

Aromatic polymers which are hydrogenated by such processes include any polymeric material containing pendant aromatic functionality. Pendant aromatic functionality refers to a structure wherein the aromatic group is a substituent on the polymer backbone and not embedded therein. Preferred aromatic groups are C₆.₂o aryl groups, especially phenyl. These polymers may also contain other olefinic groups in addition to the aromatic groups. Preferably, the polymer is derived from a monomer of the formula:

R '

Ar-C=C__2

wherein R is hydrogen or alkyl, Ar is phenyl, halophenyl, alkylphenyl, alkylhalophenyl, naphthyl, pyridinyl, or anthracenyl, wherein any alkyl group contains 1 to 6 carbon atoms which may be mono or multisubstituted with functional groups such as halo, nitro, amino, cyano, carbonyl and carboxyl. More preferably Ar is phenyl or alkyl phenyl with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene, and mixtures thereof. Homopolymers may have any stereostructure including syndiotactic, isotactic or atactic; however, atactic polymers are preferred. In addition, hydrogenated copolymers containing these aromatic monomers including random, pseudo random, block and grafted copolymers may be used in accordance with the present invention. For example, copolymers of vinyl aromatic monomers and comonomers selected from nitriles, acrylates, acids, ethylene, propylene, maleic anhydride, maleimides, vinyl acetate, and vinyl chloride may also be used such as styrene-acrylonitrile, styrene-alpha-methylstyrene and styrene-ethylene. Hydrogenated block copolymers of vinyl aromatic monomers and conjugated dienes such as butadiene, isoprene may also be used. Examples include styrene-butadiene, styrene-isoprene, styrene-butadiene-styrene and styrene-isoprene- styrene copolymers. Further examples of block copolymers may be found in U.S. patents 4,845,173, 4,096,203, 4,200,718, 4,210,729, 4,205,016, 3,652,516, 3,734,973, 3,390,207, 3,231 ,635, and 3,030,346. Blends of such hydrogenated polymers with other polymers including impact modified, grafted rubber containing hydrogenated vinyl aromatic polymers may also be used.

The number average molecular weight (M_n)of a hydrogenated vinyl aromatic homopolymer, if used, is typically from 1 ,000, generally from 20,000, preferably from 50,000, more preferably from 100,000 and most preferably from 200,000 to 400,000, preferably to 375,000, more preferably to 350,000 and most preferably to 325,000. M_n is determined by gel permeation chromatography.

The number average molecular weight (M_n) of a hydrogenated copolymer, if used, is typically from 30,000, preferably from 40,000, more preferably from 45,000 and most preferably from 50,000 to 120,000, typically to 100,000, generally to 95,000, preferably to 90,000, more preferably to 85,000, and most preferably to 80,000.

For purposes of the present invention, the number average molecular weight is determined using gel permeation chromatography(GPC).

The stabilizer composition comprises a hindered amine light stabilizer (HALS) and a UV absorber. Hindered amine light stabilizers are generally known in the art and can be any sterically hindered amine which will act as a light stabilizer. Such compounds include bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, dimethyl succinate polymer with 4-hydroxy- 2,2,6,6-tetramethyl-1 -piperidineethanol, and Tinuvin™ 123, Tinuvin™ 765, and

Chimassorb™ 944, all compounds which are available from Ciba Geigy Corporation. UV light absorbers are also known in the art and typically include compounds containing benzotriazole functionality. Such compounds include, but are not limited to 2-(2H- benzotriazol-2-yl)-4,6-bis(1 -methyl-1-phenylethyl)phenol, and Tinuvin™ P, Tinuvin™ 213, Tinuvin™ 326, Tinuvin™ 327, Tinuvin™ 328, Tinuvin™ 329, and Tinuvin™ 571 , all compounds which are available from Ciba Geigy Corporation. They are used in ratios of from 1 :99 to 99:1 weight percent amine:UV absorber , preferably from 50:50 to 83:17, more preferably from 66:34 to 80:20, based on the total weight of the stabilizer composition. The stabilizer composition is typically combined with the hydrogenated vinyl aromatic polymer at a level of from 0.05, generally from 0.08, preferably from 0.15, more preferably from 0.2 and most preferably from 0.3 to 1 , generally to 0.9, preferably to 0.8 more preferably to 0.75 and most preferably to 0.7 parts per hundred (pph), based on the weight of the hydrogenated vinyl aromatic polymer.

The stabilizers can be combined with the hydrogenated vinyl aromatic polymer by any conventional method. The stabilizers can be pre-mixed prior to addition to the polymer or each component can be individually added to the polymer. The stabilizers can be dry blended with pellets of hydrogenated vinyl aromatic polymer prior to melt processing, but are preferably melt blended or mixed with hydrogenated vinyl aromatic polymer prior to devolatilization and pelletization.

Other additives may be present in the composition of the invention as long as the UV stability is not further modified. Typical additives include viscosity modifiers such as mineral oil and low M_n hydrogenated vinyl aromatic polymers and hydrogenated copolymers of styrene, α-methyl styrene, vinyl toluene, and/or indene, and mold release additives. Other types of stabilizers may also be present.

In one embodiment of the present invention, the composition additionally comprises a heat stabilizer composition. To maintain the M_n and thus the excellent physical properties of the hydrogenated vinyl aromatic polymer, a stabilizer combination is used which prevents polymer degradation during processing at high temperatures, such as temperatures up to 350°C. In one embodiment the stabilizer combination consists of a benzofuranone and a hindered phenol. Typical benzofuranones and methods of producing are described in U.S. Patent No. 4,325,863. In a most preferred embodiment, the benzofuranone is 5,7-di-t-butyl- 3-(3,4-di-methylphenyl)-3H-benzofuran-2-one(CAS No. 181314-48-7).

The benzofuranone is advantageously present in amounts of from 10, generally from 20, typically from 30, preferably from 50, more preferably from 100 and most preferably from 200 ppm to 4000, generally to 2000, typically to 1000, preferably to 800, more preferably to 600 and most preferably to 400 ppm, based on the weight of the hydrogenated vinyl aromatic polymer.

The hindered phenol used in the heat stabilizer composition can be any sterically hindered phenol which will act as a heat stabilizer for the hydrogenated vinyl aromatic polymer composition. Typical hindered phenols include β-(4-hydroxy-3,5-ditert.- butylphenyl)-propionicacidstearylester, tetrakis[methylene-3(3',5'-ditert-butyl-4- hydroxyphenyl)-propionate]-methane, 1 ,3,3-tris(2-methyl-4-hydroxy-5-tert.-butylphenyl)- butane,1 ,3,5-tris(4-tert.-butyl-3-hydroxy-2,6-dimethylbenzyl)-1 ,3,5-triazine-2,4,6-(1 H,3H,5H)- trione, bis(4-tert.-butyl-3-hydroxy-2,6-dimethylbenzyl)-dithiol-terephthalate, tris(3,5-ditert.- butyl-4-hydroxybenzyl-isocyanurate, triester of 3,5-di-tert.-butyl-4-hydroxyhydro-cinnamic acid with 1 ,3,5-tris-(2-hydroxyethyl)-s-triazin-2,4,6-(1 H,3H,5H)-trione, bis[3,3-bis-4'hydroxy- 3-tert-butylphenyl)-butaneacid]-glycolester, 1 ,3,5-trimethyl-2,4,6-tris-(3,5-ditert-butyl-4- hydroxybenzyl)-benzene, 2,2'methylenebis(4-methyl-6-tert-butylphenyl)terephthalate, 4,4- methylene-bis-(2,6-ditert-butylphenol), 4,4'-butylidene-bis(6-tert-butyl-meta-cresol), 4,4-thio- bis(2-tert-butyl-5-methylphenol), 2,2'-methylene-bis(4-methyl-6-tert-butylphenol) and octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate.

Hindered phenols are advantageously present in the composition of the present invention in amounts of from 0.01 , generally from 0.03, typically from 0.05, preferably from 0.1 , more preferably from 0.15 and most preferably from 0.20 to 1 , generally to 0.8, typically to 0.6, preferably to 0.5, more preferably to 0.4 and most preferably to 0.3 weight percent based on the weight of the hydrogenated vinyl aromatic polymer.

Generally, the ratio of the benzofuranone to the hindered phenol is 99:1 to 1 :99. Typically, the ratio is 75:25 to 25:75, preferably 50:50 to 25:75, more preferably 20:80 to 10:90, and most preferably 15:85.

The heat stabilizer composition can be combined with the hydrogenated vinyl aromatic polymer composition by any conventional method. The stabilizers can be pre- mixed prior to addition to the polymer or each component can be individually added to the polymer. The stabilizers can be dry blended with pellets of hydrogenated vinyl aromatic polymer, but are preferably dissolved in or melt blended with the hydrogenated vinyl aromatic polymer, and more preferably mixed with hydrogenated vinyl aromatic polymer prior to devolatilization and pelletization.

The composition of the present invention is useful in a variety of applications, including high heat lighting and outdoor exposure applications.

The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.

EXAMPLES

The polymers listed in Table I are mixed with the indicated stabilizer packages by shake mixing the stabilizers and polymer in a bag. The mixture is than injection molded into a 5 cm diameter disc with a thickness of approximately 3.2 mm. The discs are then exposed to a 400 watt metal halide light in a temperature controlled chamber at 100°C. The samples are removed every 50 hours and the yellowness index (Yl) is measured. The samples are then returned for further testing. The results are listed in Table I.

TABLE I

"Comparative Examples

Amine is bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate

UV absorber is 2-(2H-benzotrizol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol

PVCH is a polyvinylcyclohexane homopolymer having less than 1 percent residual unsaturation and a number average molecular weight (M_n) of approximately 300,000

Yl is the Yellowness Index measured according to ASTM D1925

The combination of hindered amine and UV absorber with the hydrogenated vinyl aromatic polymer gives superior results in yellowness when compared to the amine or UV absorber alone.

Claims

CLAIMS:

1. A composition comprising:

a) a hydrogenated vinyl aromatic homopolymer or copolymer, and

b) a light stabilizer mixture comprising:

1 ) a hindered amine, and

2) a ultraviolet (UV) light absorber.

2. The composition of Claim 1 wherein the hydrogenated vinyl aromatic polymer is polyvinylcyclohexane.

3. The composition of Claim 1 wherein the hydrogenated vinyl aromatic polymer is a hydrogenated block copolymer of styrene and butadiene.

4. The composition of Claim 1 wherein the hindered amine is selected from the group consisting of bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1 -piperidineethanol, Tinuvin™ 123, Tinuvin™ 765, and Chimassorb™ 944.

5. The composition of Claim 1 wherein the UV light absorber is selected from the group consisting of 2-(2H-benzotriazol-2-yl)-4,6-bis(1 -methyl-1 -phenylethyl)phenol, and Tinuvin™ P, Tinuvin™ 213, Tinuvin™ 326, Tinuvin™ 327, Tinuvin™ 328, Tinuvin™ 329, and Tinuvin™ 571.

6. The composition of Claim 1 wherein the ratio of hindered amine to UV light absorber is from 1 :99 to 99:1.

7. The composition of Claim 1 wherein the ratio of hindered amine to UV light absorber is 50:50 to 83:17.

8. The composition of Claim 1 wherein the ratio of hindered amine to UV light absorber is 66:34 to 80:20.

9. The composition of Claim 1 wherein the stabilizer composition is present in an amount of from 0.05 to 1 pph, based on the amount of hydrogenated vinyl aromatic homopolymer or copolymer.

10. The composition of Claim 1 wherein the stabilizer composition is present in an amount of from 0.0.3 to 0.7 pph, based on the amount of hydrogenated vinyl aromatic homopolymer or copolymer.

11. The composition of Claim 1 also comprising a heat stabilizer composition.

12. An article prepared from the composition of Claim 1.