WO1999020449A1

WO1999020449A1 - Injection-molded articles made from long chain branched syndiotactic monovinylidene aromatic polymers

Info

Publication number: WO1999020449A1
Application number: PCT/US1998/018666
Authority: WO
Inventors: Norbert L. Maecker; Yi-Bin Huang; Kevin L. Nichols
Original assignee: The Dow Chemical Company
Priority date: 1997-10-17
Filing date: 1998-09-04
Publication date: 1999-04-29
Also published as: CN1276754A; CA2304680A1; KR20010031091A; EP1023151A1; JP2001520277A; AU9380198A

Abstract

The present invention is directed to injection-molded articles prepared from a composition comprising a long chain branched syndiotactic mononvinylidene aromatic polymer. Long chain branches can be produced during polymerization by polymerizing in the presence of a small amount of a difunctional monomer.

Description

INJECTION-MOLDED ARTICLES MADE FROM LONG CHAIN BRANCHED SYNDIOTACTIC MONOVINYLIDENE AROMATIC POLYMERS The present invention relates to syndiotactic monovinylidene aromatic polymers and injection-molded articles produced therefrom. Syndiotactic monovinylidene aromatic polymers such as syndiotactic polystyrene (SPS) are useful polymers having a high melting point and crystallization rate as well as excellent heat and chemical resistance. However, in some applications such as in injection-molded articles for electronic connectors and automotive parts, the melt flow rate or crystallization rate is insufficient when injection molding to obtain desired properties.

Syndiotactic copolymers have also been developed having superior heat and chemical resistance. US-A-5,202,402 issued to Funaki et al. utilizes a difunctional monomer to form a syndiotactic copolymer with styrene, however, the polymer fully crosslinks at high temperatures, forming a thermoset and cannot be melt processed to produce injection-molded articles.

Injection-molded articles have been produced from linear syndiotactic monovinylidene aromatic polymers as described in US-A-5,034,441 , 5,326,813; 5,444,126, 5,418,275, and EP-312976, EP-733675, and EP-736364. However, the melt flow rates and crystallization rates of linear syndiotactic monovinylidene aromatic polymers are sometimes too low to produce injection-molded articles, especially, thin- wall injection-molded articles, with desirable properties such as low molded in stress, sufficient crystaliinity, and uniform crystallinity.

Therefore, it would be useful to obtain injection molded articles from a syndiotactic monovinylidene aromatic polymer having good heat and chemical resistance, with high melt flow and crystallization rate.

The present invention is directed to injection-molded articles prepared from a composition comprising a long chain branched syndiotactic monovinylidene aromatic polymer. Long chain branches can be produced during polymerization by polymerizing in the presence of a small amount of a difunctional monomer. The injection-molded articles of the present invention have less molded in stress, require less pressure for filling and have a more uniform and higher level of crystallinity, which manifests itself in improved heat performance and mechanical properties such as high temperature creep when compared to those made of linear syndiotactic monovinylidene aromatic polymer. In one embodiment, the present invention is an injection-molded article prepared from a composition comprising a long chain branched syndiotactic monovinylidene aromatic (LCB-SVA) polymer.

As used herein, the term "syndiotactic" refers to polymers having a stereoregular structure of greater than 90 percent syndiotactic, preferably greater than 95 percent syndiotactic, of a racemic triad as determined by 13C nuclear magnetic resonance spectroscopy.

Syndiotactic monovinylidene aromatic polymers are homopolymers and copolymers of vinyl aromatic monomers, that is, monomers whose chemical structure possess both an unsaturated moiety and an aromatic moiety. The preferred vinyl aromatic monomers have the formula:

H₂C=CR-Ar; wherein R is hydrogen or an alkyl group having from 1 to 4 carbon atoms, and Ar is an aromatic radical of from 6 to 10 carbon atoms. Examples of such vinyl aromatic monomers are styrene, alpha-methylstyrene, ortho-methylstyrene, meta- methylstyrene, para-methylstyrene, vinyl toluene, para-t-butylstyrene, and vinyl naphthalene; bromo- substituted styrenes, especially p-vinyltoluene and ring brominated or dibrominated styrenes. Brominated styrenes are particularly useful in the preparation of ignition resistant syndiotactic monovinylidene aromatic polymers. Alternatively, ignition resistant LCB-SVA polymers can be produced by brominating LCB-SVA polymers. Representative syndiotactic copolymers include styrene-p- methylstyrene, styrene-p-t-butylstyrene and styrene-toluene copolymers. Syndiotactic monovinylidene aromatic polymers and monomers made therefrom are known in the art having been previously disclosed in, for example, US-A-4,680,353; US-A-4,959,435; US-A-4,950,724; and US-A-4,774,301. Syndiotactic polystyrene is the currently preferred syndiotactic monovinylidene aromatic polymer.

Long chain branching can be achieved by polymerizing a vinyl aromatic monomer in the presence of a small amount of a multifunctional monomer under conditions sufficient to produce a syndiotactic monovinylidene aromatic polymer. A multifunctional monomer is any compound having more than one oiefinic functionality which can react with a vinyl aromatic monomer under polymerization conditions. Typically, the multifunctional monomer will contain 2-4 oiefinic functionalities and is represented by formula (I):

(R)n wherein R is a vinyl group or a group containing from 2 to 20 carbon atoms including a terminal vinyl group, wherein the groups containing 2 to 20 carbon atoms may be alkyl, alkenyi, cycloalkyl, or aromatic, wherein cycloalkyl groups contain at least 5 carbon atoms and aromatic groups contain at least 6 carbon atoms, n is an integer from 1 to 3 wherein the R groups are meta or para in relation to the vinyl group of formula (I), and when n is greater than 1 , R may be the same or different. Preferably R is a vinyl group.

Preferably the multifunctional monomer contains two terminal vinyl groups wherein n would equal 1. Typically, such monomers include difunctional vinyl aromatic monomers such as di-vinyl-benzene or di-styryl-ethane.

The amount of multifunctional monomer will depend upon the weight average molecular weight (Mw) of the polymer to be produced, but typically is from 10, preferably from 50, more preferably from 75, and most preferably from 100 ppm to 1000, preferably to 800, more preferably to 500, and most preferably to 650 ppm, based on the amount of vinyl aromatic monomer.

The multifunctional monomer can be introduced into the polymerization by any method which will allow the multifunctional monomer to react with the vinyl aromatic monomer during polymerization to produce a LCB-SVA polymer. For example, the multifunctional monomer can be first dissolved in the vinyl aromatic monomer prior to polymerization or introduced separately into the polymerization reactor before or during the polymerization. Additionally, the multifunctional monomer can be dissolved in an inert solvent used in the polymerization such as toluene or ethyl benzene. Any polymerization process which produces syndiotactic monovinylidene aromatic polymers can be used to produce the LCB-SVA polymers of the present invention as long as a multifunctional monomer is additionally present during polymerization. Typical polymerization processes for producing syndiotactic monovinylidene aromatic polymers are well known in the art and are described in US-A-4,680,353, US-A-5,066,741 , US-A-5,206,197 and US-A-5,294,685.

Typically, the weight average molecular weight (Mw) of the LCB-SVA polymer is from 50,000, preferably from 100,000, more preferably from 125,000, and most preferably from 150,000 to 3,000,000, preferably to 1 ,000,000, more preferably to 500,000 and most preferably to 350,000.

A branched syndiotactic monovinylidene aromatic polymer contains extensions of syndiotactic monovinylidene aromatic polymer chain attached to the polymer backbone. A long chain branched syndiotactic monovinylidene aromatic polymer typically contains chain extensions of at least 10 monomer repeating units, preferably at least 100, more preferably at least 300, and most preferably at least 500 monomer repeating units.

Typically, the injection-molded articles of the present invention are produced from a composition of a LCB-SVA polymer without the presence of other polymers. However, injection-molded articles may be produced from compositions comprising a LCB-SVA polymer and other components including other polymers. The amount of LCB-SVA polymer contained within a composition for producing injection-molded articles is dependent upon the final application wherein advantages may be obtained with only small amounts in some instances. Generally, at least 5 percent by weight of a LCB-SVA polymer is used in a composition for producing injection-molded articles, typically at least 20 percent, preferably at least 40 percent, more preferably at least 70 percent and most preferably 100 percent. Other polymers which may be included in such compositions include but are not limited to linear SPS, polystyrene, polyphenylene oxide, polyolefins, such as polypropylene, polyethylene, poly(4- methylpentene), ethylene-propylene copolymers, ethyene-butene-propylene copolymers, nylons, for example nylon-6, nylon-6,6; polyesters, such as poly(ethylene terephthalate), poly utylene terephthalate); and copolymers or blends thereof. Other materials or additives, including antioxidants, impact modifiers, ignition resistant agents, coupling agents, for example maleated polymers, including maleic anhydride modified polyphenylene oxide, or maleic anhydride modified syndiotactic monovinylidene aromatic polymers, binders to improve the wet strength of a base fabric, flame retardants including brominated polystyrene, brominated syndiotactic monovinylidene aromatic polymers, brominated aromatic compounds, antimony trioxide, and polytetrafluoroethylene may be added to the LCB-SVA polymer composition, or the injection-molded articles made therefrom. Impact modifiers which can be used in the LCB-SVA polymer composition include block or graft copolymers of vinyl aromatic and butadiene or isoprene monomers, substantially random interpolymers of an alpha-olefin and a vinyl aromatic monomer, and polyolefin elastomers. The term "interpolymer" as used herein refers to polymers prepared by the polymerization of at least two different monomers. The generic term interpolymer thus embraces copolymers, usually employed to refer to polymers prepared from two different monomers, and polymers prepared from more than two different monomers.

While describing in the present invention a polymer or interpolymer as comprising or containing certain monomers, it is meant that such polymer or interpolymer comprises or contains polymerized therein, units derived from such a monomer. For example, if the monomer is ethyiene CH₂=CH₂, the derivative of this unit as incorporated in the polymer is -CH₂-CH₂-.

The vinyl aromatic monomers contained in the substantially random interpolymers of an alpha-olefin and a vinyl aromatic monomer interpolymers include those vinyl aromatic monomers described previously as monomers useful for preparing the syndiotactic monovinylidene aromatic polymers.

The aliphatic alpha-olefin monomers contained in the interpolymers include aliphatic and cycloaliphatic alpha-olefins having from 2 to 18 carbon atoms, and preferably alpha-olefins having from 2 to 8 carbon atoms. Most preferably, the aliphatic alpha-olefin comprises ethyiene or propylene, preferably ethyiene, optionally together with one or more other alpha-olefins having from 3 to 8 carbon atoms, such as for example ethyiene and propylene, or ethyiene and octene, or ethyiene and propylene and octene. The interpolymers are preferably a pseudo-random linear or substantially linear, more preferably a linear interpolymer comprising an aliphatic alpha-olefin and a vinyl aromatic monomer. These pseudo-random linear interpolymers are described in EP-A-0,416,815.

The substantially random interpolymers may be modified by typical grafting, hydrogenation, functionalizing, or other reactions well known to those skilled in the art, provided their impact or ductility modification function will not be substantially affected. The polymers may be readily sulfonated or chlorinated to provide functionalized derivatives according to established techniques.

The pseudo-random interpolymers can be prepared as described in EP-A- 0,416,815. Preferred operating conditions for such polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from 30°C to 200°C.

Examples of suitable catalysts and methods for preparing the pseudo-random interpolymers are disclosed in EP-A-416,815; EP-A-468,651 ; EP-A-514,828; EP-A- 520,732, WO 93/23412, US-A-5,347,024, US-A-5,470,993, US-A-5,624,878, US-A-5,556,928„ as well as US-A-5,055,438, US-A-5,057,475, US-A-5,096,867, US-A-5,064,802, US-A-5,132,380, and US-A-5,189,192.

Elastomeric polyolefin impact modifiers can be any elastomeric polyolefin such as those described in US-A-5,460,818. Elastomeric polyolefins include any polymer comprising one or more C₂-₂₀ α-olefins in polymerized form, having Tg less than 25°C, preferably less than 0°C. Examples of the types of polymers from which the present elastomeric polyolefins are selected include homopolymers and copolymers of α-olefins, such as ethylene/propylene, ethylene/1-butene, ethylene/1- hexene or ethylene/1 -octene copolymers, and terpolymers of ethyiene, propylene and a comonomer such as hexadiene or ethylidenenorbornene. Grafted derivatives of the foregoing rubbery polymers such as polystyrene-, maleic anhydride-, polymethylmethacrylate- or styrene/methyl methacrylate copoiymer-grafted elastomeric polyolefins may also be used.

The LCB-SVA polymer compositions may also contain inorganic reinforcing agents. Suitable reinforcing agents include any mineral, glass, ceramic, polymeric or carbon reinforcing agent fillers such as glass fibers, micas, talcs, carbon fibers, wollastonite, graphite, silica, magnesium carbonate, alumina, metal fibers, kaolin, silicon carbide, and glass flake. Such material may be in the shape of fibers having a length to diameter ratio (L/D) of greater than 5. Preferred particle diameters are from 0.1 micrometers to 1 millimeter. Preferred reinforcing agents are glass fibers, glass roving or chopped glass fibers having lengths from 0.1 to 10 millimeters and LVD from 5 to 100. Three such suitable glass fibers are available from Owens Corning Fiberglas under the designation OCF-187A or 497 or from PPG under the designation 3540. Suitable fillers include nonpolymeric materials designed to reduce the coefficient of linear thermal expansion of the resulting material, to provide color or pigment thereto, to reduce the flame propagation properties of the composition, or to otherwise modify the composition's physical properties. Suitable fillers include mica, talc, chalk, titanium dioxide, clay, alumina, silica, glass microspheres, wollastonite, calcium carbonate, magnesium sulfate, barium sulfate, calcium oxysulfate, tin oxide, metal powder, glass powder, and various pigments. Preferred fillers are in the shape of particulates having (L D) less than 5. The amount of reinforcing agent or filler employed is preferably from 10 to 50 parts by weight. Preferred fillers are talcs with number average diameter less than 1 micron such as MP 10-52 available form Mineral Technologies and wollastonite with number average diameter less than 5 such as Jilin 2000 available from GLS.

The reinforcing agent may include a surface coating of a sizing agent or similar coating which, among other functions, may promote adhesion between the reinforcing agent and the remaining Components, especially the matrix, of the composition. Suitable sizing agents may contain amine, aminosilane, epoxy, and aminophosphine functional groups and contain up to 30 nonhydrogen atoms.

Preferred are aminosilane coupling agents and C alkoxy substituted derivatives thereof, especially 3-aminopropyltrimethoxysilane.

The LCB-SVA polymer compositions may also contain other additives including lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethyiene bis-stearamide, pentaerythritol tetrastearate, organo phosphate, mineral oil, trimellitate, polyethylene glycol, silicone oil, epoxidized soy bean oil, tricresyl phosphate, polyethylene glycol dimethyl ether, dioctyl adipate, di-n-butyl phthalate, butylene glycol montanate (Wax OP), pentaerythritol tetramontanate (TPET 141 ), aluminum mono-stearate, aluminum di-stearate, montanic acid wax, montanic acid ester wax, polar polyethylene waxes, and non- polar polyethylene waxes. Other additives include polyarylene ethers such as those described in US-A-3,306,874, US-A-3,306,875, US-A-3,257,357, and US-A-3,257,358. A preferred polyarylene ether is poly(2,6-dimethyl-1 ,4- phenylene)ether. The polyphenylene ethers are normally prepared by an oxidative coupling reaction of the corresponding bisphenol compound. Preferred polyarylene ethers are polar group functionalized polyarylene ethers, which are a known class of compounds prepared by contacting polar group containing reactants with polyarylene ethers. The reaction is normally conducted at an elevated temperature, preferably in a melt of the polyarylene ether, under conditions to obtain homogeneous incorporation of the functionalizing reagent. Suitable temperatures are from 150°C to 300°C.

Suitable polar groups include the acid anhydrides, acid halides, acid amides, sulfones, oxazolines, epoxies, isocyanates, and amino groups. Preferred polar group containing reactants are compounds having up to 20 carbons containing reactive unsaturation, such as ethylenic or aliphatic ring unsaturation, along with the desired polar group functionality. Particularly preferred polar group containing reactants are dicarboxylic acid anhydrides, most preferably maleic anhydride. Typically the amount of polar group functionalizing reagent employed is from 0.01 percent to 20 percent, preferably from 0.5 to 15 percent, most preferably from 1 to 10 percent by weight based on the weight of polyarylene ether. The reaction may be conducted in the presence of a free radical generator such as an organic peroxide or hydroperoxide agent if desired. Preparation of polar group functionalized polyarylene ethers have been previously described in US-A-3,375,228, US-A-4,771 ,096 and US-A-4,654,405. The polar group modified polyarylene ethers beneficially act as compatibilizers to improve adhesion between the reinforcing agent and the syndiotactic monovinylidene aromatic polymer. Thus, their use is particularly desirable when a filler or reinforcing agent is additionally utilized. The amount of polyarylene ether employed in the present resin blend is beneficially from 0.1 to 50 parts by weight, preferably from 0.2 to 10 parts by weight based on 100 parts glass and polyarylene ether. The polar group modified polyarylene ether may be in the form of a coating applied to the outer surface of the reinforcing agent to impart added compatibility between the reinforcing agent and the polymer matrix. The polar group modified polyarylene ether so utilized may be in addition to further amounts of polyarylene ether or polar group modified polyarylene ether also incorporated in the blend. The surface coating is suitably applied to the reinforcing agent by contacting the same with a solution or emulsion of the polar group functionalized polyarylene ether. Suitable solvents for dissolving the polar group functionalized polyarylene ether to form a solution or for use in preparing an emulsion of a water-in-oil or oil-in-water type include methylene chloride, trichloromethane, trichloroethylene and trichloroethane. Preferably the concentration of polar group functionalized polyarylene ether in the solution or emulsion is from 0.1 weight percent to 20 weight percent, preferably 0.5 to 5 percent by weight. After coating of the reinforcing agent using either a solution or emulsion, the liquid vehicle is removed by, for example, evaporation, devolatilization or vacuum drying. The resulting surface coating is desirably from 0.001 to 10 weight percent of the uncoated reinforcing agent weight. Other additives useful in the LCB-SVA polymer compositions include nucleators capable of reducing the time required for the onset of crystallization of the syndiotactic monovinylidene aromatic polymer upon cooling from the melt. Nucleators provide a greater degree of crystallinity in a molding resin and more consistent distribution of crystallinity under a variety of molding conditions. Higher levels of crystallinity are desired in order to achieve increased chemical resistance and improved heat performance. In addition crystal morphology may be desirably altered. Examples of suitable nucleators for use herein are monolayer of magnesium aluminum hydroxide, calcium carbonate, mica, wollastonite, titanium dioxide, silica, sodium sulfate, lithium chloride, sodium benzoate, aluminum benzoate, talc, and metal salts, especially aluminum salts or sodium salts of organic acids or phosphonic acids. Especially preferred compounds are aluminum and sodium salts of benzoic acid and C_M0 alkyl substituted benzoic acid derivatives. A most highly preferred nucleator is aluminum tris(p-tert-butyl)benzoate. The amount of nucleator used should be sufficient to cause nucleation and the onset of crystallization in the syndiotactic vinylaromatic polymer in a reduced time compared to compositions lacking in such nucleator. Preferred amounts are from 0.5 to 5 parts by weight.

Other additives may also be included in the composition of the present invention including additives such as flame retardants, pigments, and antioxidants, including IRGANOX™ 1010, 555, 1425 and 1076, IRGAFOS™ 168, CGL-415, and GALVINOXYL™ available from Ciba Geigy Corporation, SEENOX™ 412S available from Witco, ULTRANOX™ 626 and 815 available from GE Specialty Chemicals, MARK PEP™ 36 available from Adeka Argus, AGERITE™ WHITE, MA and DPPD, METHYL ZIMATE, VANOX™ MTI and 12 available from R.T. Vanderbilt, NAUGARD™ 445 and XL-1 available from Uniroyal Chemical, CYANOX™ STDP and 2777 available from American Cyanamid, RONOTEC™ 201 (Vitamin E) available from Roche, MIXXIM CD-12 and CD-16 available from Fairmount, Ethanox™ 398, DHT-4a, SAYTEX™ 8010, 120, BT93 and 102 available from Ethyl, Hostanox™ PAR 24, 03, and ZnCS1 available from Hoechst Celanese, cesium benzoate, sodium hydroxide, SANDOSTAB™ PEPQ available from Sandoz, t-butyl hydroquinone, and SANTOVAR™ A available from Monsanto, phenothiazine, pyridoxine, copper stearate, cobalt stearate, MOLYBDENUM TENCEM available from Mooney Chemicals, ruthenium (III) acetylacentonate, boric acid, citric acid, MARK 6000 available from Adeka Argus, antimony oxide, 2,6-di-t-butyl-4-methylphenol, stearyl-β- (3,5-di-tert-butyl-4-hydroxyphenol)propionate, and triethylene glycol-bis-3-(3-tert- butyl-4-hydroxy-5-methylphenyl)propionate, tris(2,4-tert-butylphenyl)phosphite and 4,4'-butylidenebis(3-methyl-6-tert-butyiphenyl-di-tridecyl)-phosphite; tris nonyl phenyl phosphite, carbon black, PYROCHEK PB68 available from Ferro Corporation, decabromodiphenyl oxide, antiblock agents such as fine particles composed of alumina, silica, aluminosilicate, calcium carbonate, calcium phosphate, and silicon resins; light stabilizers, such as a hindered amine-based compounds or benzotriazole-based compounds; plasticizers such as an organopolysiloxane or mineral oil; blowing agents, extrusion aids, stabilizers such as bis(2,4-di- tertbutylphenyl)pentaerythritol and tris nonyl phenyl phosphite.

The injection-molded articles of the present invention can be made by various processes including direct injection molding, gas-assist injection molding, co-injection molding, reciprocating screw injection molding, multi-station reciprocating screw injection molding, multi-station screw/RAM injection molding, and blow molding. Typically, the injection-molded articles of the present invention are from approximately 0.1 to 10 mm. thick, more preferably 0.5 to 5 mm. thick. The injection-molded articles of the present invention can also be coated or laminated with other material to add additional properties to the injection-molded articles. The injection-molded articles of the present invention can be used in electronic connectors, electric connectors, electrical components, automotive under-the-hood parts, lighting parts, automotive air induction parts, automotive coolant system parts, and battery seals.

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

PRODUCTION OF LCB-SVA

All reactions are conducted under inert atmosphere in a dry box. The reagents, toluene and styrene monomer are purified and handled using standard inert atmosphere techniques. Di-styryl-ethane (DSE) is prepared following the procedure described in J. Polymer Sci., Part A, Polymer Chem., 32 (1994) 2023 by W.H. Li, et al.

A 10 percent methylalumoxane in toluene solution, 1 Molar triisobutylaluminum in toluene and a 0.03 Molar solution of pentamethylcyclopentadienyl-titanium trimethoxide in toluene are mixed in a dry box in volumetric flasks in ratios of 75:25:1 with a final concentration of the catalyst solution, based on titanium, of 0.003 Molar.

4.54 gm of styrene are charged into 4 ampoules. A 1 percent solution of di- styryl-ethane (DSE) in toluene, is added at the ppm level indicated below. The ampoules are then sealed and equilibrated at the polymerization temperature of 70°C for 10 minutes. Polymerization is initiated by addition of catalyst solution in mole ratio of styrene to titanium of 175,000:1. The polymerization is quenched by the addition of an excess of methanol after one hour. The polymer is isolated and dried and molecular weight is determined via high temperature size exclusion chromatography. The results are shown below.

m DSE % Conversion Mn Mw Mz Mw/Mn

0 82 98,700 345,000 684,600 3.50

200 86 67,500 496,900 1 ,126,100 7.36

400 85 125,800 662,400 1,768,000 5.27

800 79 104,900 659,300 1,703,700 6.28

The significant increase in Mz with di-styryl-ethane is an indication of long chain branching in the SPS polymer.

Larger scale reactions are conducted in a 5" Teledyne kneader-mixer which is described in US-A-5,254,647. A solution of 1.3 wt. percent di-styryl-ethane in toluene is added to styrene monomer in the amounts listed in Table I and fed to the reactor at 17.5 kg/hr giving a mean residence time of 18 minutes. The polymerization is conducted at temperatures of 55 to 67.5 °C. A catalyst solution of methylaiuminoxane, triisobutylaluminum and octahydrofluorenyl titanium trimethoxide catalyst is fed to the reactor at styrene to titanium mole ratios of 80,000:1 to 100,000:1. The product is a fine, white-powder ranging in conversion from 36 to 50 percent. The samples are collected under nitrogen and quenched by the addition of an excess of methanol. The samples are then dried in a nitrogen-swept, 220 °C, 5mm Hg vacuum oven for two hours. The weight average molecular weight (Mw) of the polymer is determined by high temperature size exclusion chromatography. The results are shown in Table I:

Table I

The significant increase in Mz with di-styryl-ethane is an indication of long chain branching. The above samples, in the form of powders, are converted to pellets using a 0.5" single-screw extruder. The molecular weight of the pellets are summarized below:

Melt strength is measured according to the technique described in Plastics Engineering, 51 , (2), 25, 1995 by S. K. Goyal with the test conditions of 1 in./min. plunger speed, 50 ft./min. winder rate and 279°C. Melt flow rate is measured according to ASTM method D1238 with the test conditions of 1.2 Kg load and 300°C. A 300,000 Mw linear SPS polymer is used as the control. The results are summarized below:

The LCB-SPS samples have higher melt strengths and higher melt flow rates than the linear SPS control sample.

EXAMPLE 1 PREPARATION OF LCB-SPS AND INJECTION-MOLDED ARTICLES THEREFROM

Polymerization reactions are carried out in a 5" Teledyne kneader-mixer, with mean residence time of 18 minutes, followed by a 500 liter tank reactor, with mean residence time of 10 hours. Operation of these devices are described in US-A-5,254,647. Styrene monomer is mixed with 250 ppm of a 3.3 percent solution of di-styryl-ethane in toluene and fed to the reactor at 17.5 kg./hr. Polymerization is carried out at a temperature of 55°C. A catalyst solution of methyaluminoxane, triisobutylaluminum and octahydrofluorenyltitanium trimethoxide is also fed to the reactor at styrene to titanium mole ratios of 80,000:1. After polymerization, the polymer is devolatilized and pelletized as described previously. The molecular weight of the polymer is determined via high temperature size exclusion chromatography and the results are shown below:

Mw Mn Mz Mz+1 Mw/Mn

313,900 86,100 1 ,227,500 2,729,300 3.65

A 300,000 Mw linear SPS polymer is used as a control.

The LCB-SPS and Control polymers are formulated with 30 percent glass fibers, antioxidants, nucleating agent, and mold release agent. The compositions are extruded on a 40 mm co-rotating twin-screw extruder using the following conditions:

The resulting pellets are injection molded into standard tensile bar specimens with a 100 ton injection molder. The machine set points used for molding tensile bars are the following:

The glass-filled LCB-SPS composition has a higher heat distortion temperature (461 °F) than the corresponding glass-filled linear SPS composition (373°F).

Another lot of LCB-SPS polymer is prepared in the same way as described above. The molecular weight of the polymer is determined via high temperature size exclusion chromatography and the results are shown below: Mw Mn Mz Mz+1 Mw/Mn

366,200 86,300 1 ,635,100 3,552,000 4.24

A 300,000 Mw linear SPS polymer is used as a control.

The LCB-SPS and Control polymers are formulated with 30 percent glass fibers, antioxidants, nucleating agent, mold release agent, and a flame retardant package. The compounds are extruded on a 40 mm co-rotating twin-screw extruder using the same conditions as described above. The resulting pellets are injection molded into standard tensile bar specimens with a 100 ton injection molder using the same injection molding conditions described above.

The formulated pellets are then melted and viscosities measured using the capillary tube method.

The glass-filled, ignition-resistant LCB-SPS composition has 12 to 20 percent lower viscosity than the corresponding linear SPS compound over a range of shear rates from 100 to 10000 sec^"1.

Flexural creep is determined using a Rheometrics RSA II solids analyzer fitted with a high temperature oven under a dry N₂ environment. Samples are fabricated from injection molded bars with final dimensions of 12.7 mm wide by 3.2 mm thick and at least 60 mm long. Three-point bend fixtures are used with a constant 48 mm span. The oven is set at the 250°C and equilibrated for 10 min. A 1 g compression force is placed on the sample to insure contact followed by 1.58 x 10⁶ Pa. The resulting creep strain is recorded for over 600 s resulting in 500 measurements of strain during the run.

The LCB-SPS composition also has improved resistance to creep at elevated temperatures.

Claims

1. An injection-molded article produced from a composition comprising a long chain branched syndiotactic monovinylidene aromatic polymer.

2. The injection molded article of Claim 1 wherein the composition further comprises from 10 to 50 wt. percent glass fiber based on the total weight of the composition.

3. The injection molded article of Claim 2 wherein the composition further comprises a brominated flame retardant and antimony trioxide.

4. The injection molded article of Claim 2 wherein the composition further comprises an impact modifier.

5. The injection molded article of Claim 4 wherein the impact modifier is a block or graft copolymer of a vinyl aromatic and butadiene or isoprene monomer; a substantially random interpolymer of an alpha-olefin and a vinyl aromatic monomer; or a polyolefin elastomer.

6. The injection molded article of Claim 5 wherein the impact modifier is selected from the group comprising a styrene-butadiene-styrene copolymer, a styrene-isoprene-styrene copolymer, a styrene-ethylene/butadiene-styrene copolymer, a styrene-ethylene/propylene-styrene copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, a butadiene-styrene-butadiene copolymer, a isoprene-styrene-isoprene copolymer, a hydrogenated product thereof, a ethylene- styrene interpolymer and a ethylene-octene copolymer.

7. The injection molded article of Claim 1 wherein the composition further comprises a lubricant.

8. The injection molded article of Claim 7 wherein the lubricant is selected from the group consisting of stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethyiene bis-stearamide, pentaerythritol tetrastearate, organo phosphate, mineral oil, t mellitate, polyethylene glycol, silicone oil, epoxidized soy bean oil, tricresyl phosphate, polyethylene glycol dimethyl ether, dioctyl adipate, di-n-butyl phthalate, butylene glycol montanate (Wax OP), pentaerythritol tetramontanate (TPET 141), aluminum mono-stearate, aluminum di- stearate, montanic acid wax, montanic acid ester wax, polar polyethylene waxes, and non-polar polyethylene waxes.

9. The injection molded article of Claim 1 wherein the composition further comprises a polyarylene ether.

10. The injection molded article of Claim 9 wherein the polyarylene ether is a polar group functionalized polyarylene ether.

11. The injection molded article of Claim 1 wherein the composition further comprises a nucleator.

12. The injection molded article of Claim 11 wherein the nucleator is selected from the group consisting of magnesium aluminum hydroxide monolayer, calcium carbonate, mica, wollastonite, titanium dioxide, silica, sodium sulfate, lithium chloride, sodium benzoate, aluminum benzoate, talc, aluminum salts and sodium salts of organic acids and phosphonic acids.

13. The injection molded article of Claim 1 wherein the composition further comprises an antioxidant.

14. The injection molded article of Claim 1 wherein the composition further comprises a flame retardant.