EP1053281A1 - Filled compositions of syndiotactic monovinylidene aromatic polymer and molded articles thereof - Google Patents

Abstract

The present invention is a composition comprising A) a syndiotactic monovinylidene aromatic polymer, and B) calcium silicate filler.

Description

FILLED COMPOSITIONS OF SYNDIOTACTIC MONOVINYLIDENE AROMATIC POLYMER AND MOLDED ARTICLES THEREOF The present invention relates to filled compositions of syndiotactic monovinylidene aromatic polymer and molded articles thereof. Numerous patents and patent applications disclose a syndiotactic polymer composition containing surface treated or untreated mineral or inorganic fillers including JP62257948, W09637552, US-A-5,326,813, EP-A-384,208, US-A-5,395,890, US-A-5,200,454, US-A-5,412,024, EP-557,836, JP8319386, US-A-5,109,068, EP-A-775,728, EP-307,488, JP5186658, EP-A-583,484, EP-A-591 ,823, EP-A-583,484, EP-A-591 ,823, JP6116454, JP8157668,

EP-A-611 ,802, WO8902901 , and JP7062175. These fillers enhance thermal resistance and improve mechanical properties, however, they also yield molded articles with poor surface quality and/or very poor thermal aging resistance.

JP5279530 discloses mineral fillers such as potassium titanate or calcium carbonate combined with syndiotactic styrene polymers which yield materials with the necessary surface smoothness while retaining heat resistance and mechanical properties for automotive light housings. However, these fillers do not provide adequate heat aging stability.

EP-A-633,295 discloses the use of wollastonite, zonotolite or aluminum borate whiskers in a thermoplastic or thermosetting resin for electronic parts. However, aluminum borate whiskers do not provide the heat aging stability needed in syndiotactic monovinylidene aromatic polymers.

Therefore, there remains a need for filled monovinylidene aromatic polymer compositions which will produce molded articles having a balance of heat resistance, mechanical properties, good surface smoothness and excellent heat aging stability. The present invention is a composition comprising

A) a syndiotactic monovinylidene aromatic polymer, and

B) a calcium silicate filler.

Another aspect of the present invention is a molded article made therefrom. Surprisingly, calcium silicate filler improves the thermal aging stability of syndiotactic monovinylidene aromatic polymers while improving heat resistance, mechanical properties and maintaining surface smoothness of molded articles therefrom.

In one embodiment, the present invention is a composition comprising syndiotactic monovinylidene aromatic polymer and a calcium silicate filler. Component A) is a syndiotactic monovinylidene aromatic 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 vinyl 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, vinyl naphthalene, and divinylbenzene. Syndiotactic polystyrene is the currently preferred syndiotactic vinyl aromatic polymer. Typical polymerization processes for producing syndiotactic vinyl 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.

Syndiotactic vinyl aromatic polymers also include long chain branched polymers. 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 vinyl aromatic polymer. A multifunctional monomer is any compound having more than one olefinic functionality which can react with a vinyl aromatic monomer under polymerization conditions. Typically, the multifunctional monomer will contain 2-4 olefinic 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

-2- alkyl, alkenyl, 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 and/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 5000, preferably to 200, more preferably to 1000, 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 long chain branched 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 vinyl aromatic polymers can be used to produce long chain branched polymers as long as a multifunctional monomer is additionally present during polymerization. A branched syndiotactic vinyl aromatic polymer contains extensions of syndiotactic vinyl aromatic polymer chain attached to the polymer backbone. A long chain branched syndiotactic vinyl 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. The weight average molecular weight of the syndiotactic monovinylidene aromatic polymer used in the composition is not critical, but is typically 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. Component B) is a mineral filler of CaO^»Si0 , e.g. wollastonite, or a hydrated version thereof such as zonotolite. Calcium silicates naturally occur as white acircular crystals, which can be formed into fibers or blocks. The calcium silicate can be used as naturally occurring crystals or can be crushed and sized for desired size selection. Synthetic calcium silicates can also be employed. Preferably the calcium silicate filler is wollastonite. Wollastonite varies in aspect ratio according to the crushing method used and the origin or source but generally b-wollastonite, which has a larger aspect ratio is preferred in view of its greater reinforcing effect.

The calcium silicate filler can also be coated with a surface coating of a sizing agent or similar coating which, among other functions, may promote adhesion between the calcium silicate filler and the remaining components, especially the syndiotactic monovinylidene aromatic polymer matrix of the composition. Sizing agents can significantly improve the ability to feed the calcium silicate filler during compounding. Suitable coatings include silane, amino, or epoxy based sizing agents. For improved feeding during compounding, silane based sizing agents are preferred. Methods of coating such fillers are well known in the art. The composition of the present invention typically comprises from 60, preferably from 65, and most preferably from 70 to 95, preferably to 90, and most preferably to 85 weight percent of the syndiotactic monovinylidene aromatic polymer, based on the total weight of the composition. Additionally the composition comprises from 5, preferably from 10, and most preferably from 15 to 40, preferably to 35, and most preferably to 30 weight percent calcium silicate filler, based on the total weight of the composition.

The calcium silicate can be combined with the syndiotactic vinyl aromatic polymer by any method which will adequately disperse the silicate in the polymer. Typically the calcium silicate is either combined with the polymer prior to compounding or is fed into the polymer melt during compounding. Preferably the calcium silicate is fed into the polymer melt.

Optionally, the composition of the present invention can also contain other modifiers such as a ductility modifier, Component C), in amounts of from 0 to 35 wt. percent based on the total weight of the composition. Such ductility 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 C₂.₂o -olefins in polymerized form, having Tg less than 25°C, preferably less than 0°C. Examples of elastomeric polyolefins 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 ethylene, 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 copolymer-grafted elastomeric polyolefins may also be used. Preferred elastomeric polyolefins of Component C) are such polymers that are characterized by a narrow molecular weight distribution and a uniform branching distribution. Preferred elastomeric polyolefins are linear or substantially linear ethylene interpolymers having a density from 0.85 to 0.89 g/cm³ and a melt index from 0.5 to 20 g/10 min. Such polymers are preferably those prepared using a Group 4 metal constrained geometry complex by means of a continuous solution polymerization process, such as are disclosed in US-A-5,272,236 and US-A-5,278,272. Generally, the elastomeric polyolefins of Component C) have a density of from 0.860 to 0.895 g/cm³, preferably less than 0.895, more preferably less than 0.885 and most preferably less than 0.88 g/cm³. Where melt index values are specified in the present application without giving measurement conditions, the melt index as defined in ASTM D-1238, Condition 190°C/2.16 kg (formerly known as "Condition (E)" and also known as 12) is meant.

The term "substantially linear" ethylene polymer or interpolymer as used herein in describing the elastomeric polyolefin of Component C) means that, in addition to the short chain branches attributable to intentionally added α-olefin comonomer incorporation in interpolymers, the polymer backbone is substituted with an average of 0.01 to 3 long chain branches/1000 carbons, more preferably from 0.01 long chain branches/1000 carbons to 1 long chain branches/1000 carbons, and especially from 0.05 long chain branches/1000 carbons to 1 long chain branches/1000 carbons. In contrast to the term "substantially linear", the term "linear" means that the polymer lacks measurable or demonstrable long chain branches, i.e., the polymer is substituted with an average of less than 0.01 long branches/1000 carbons.

Long chain branching is defined herein as a chain length of at least 1 carbon less than the number of carbons in the longest intentionally added α-olefin comonomer, whereas short chain branching is defined herein as a chain length of the same number of carbons in the branch formed from any intentionally added α-olefin comonomer after it is incorporated into the polymer molecule backbone. For example, an ethylene/1 -octene substantially linear polymer has backbones substituted with long chain branches of at least 7 carbons in length, but it also has

-5- short chain branches of only 6 carbons in length resulting from polymerization of 1- octene.

The presence and extent of long chain branching in ethylene interpolymers is determined by gel permeation chromatography coupled with a low angle laser light scattering detector (GPC-LALLS) or by gel permeation chromatography coupled with a differential viscometer detector (GPC-DV). The use of these techniques for long chain branch detection and the underlying theories have been well documented in the literature, for example in Zimm, G.H. and Stockmayer, W.H., J. Chem. Phvs.. Vol. 17, p. 1301 (1949) and Rudin, A., Modern Methods of Polymer Characterization. John Wiley & Sons, New York (1991 ), pp. 103-112.

A. Willem deGroot and P. Steve Chum, both of The Dow Chemical Company, at the October 4, 1994 conference of the Federation of Analytical Chemistry and Spectroscopy Society (FACSS) in St. Louis, Missouri, U.S.A., presented data demonstrating that GPC-DV is a useful technique for quantifying the presence of long chain branches in substantially linear ethylene interpolymers. In particular, deGroot and Chum found that the level of long chain branches in substantially linear ethylene homopolymer samples measured using the Zimm-Stockmayer equation correlated well with the level of long chain branches measured using ¹³C NMR.

Further, deGroot and Chum found that the presence of octene does not change the hydrodynamic volume of the polyethylene samples in solution and, as such, one can account for the molecular weight increase attributable to octene short chain branches by knowing the mole percent octene in the sample. By deconvoluting the contribution to molecular weight increase attributable to 1 -octene short chain branches, deGroot and Chum showed that GPC-DV may be used to quantify the level of long chain branches in substantially linear ethylene/1 -octene copolymers. deGroot and Chum also showed that a plot of Log (12, Melt Index) as a function of Log (GPC, Weight Average Molecular Weight) as determined by GPC-DV illustrates that the long chain branching aspects (but not the branching extent) of substantially linear ethylene polymers are comparable to that of high pressure, highly branched low density polyethylene (LDPE) and are clearly distinct from ethylene polymers produced using Ziegler-type catalysts such as hafnium and vanadium complexes.

The empirical effect of the presence of long chain branching in the substantially linear ethylene/α-olefin interpolymers used in the invention is manifested as enhanced rheological properties which are quantified and expressed herein in

-6- terms of gas extrusion rheometry (GER) results, and/or in terms of melt flow ratio

(110/12) increase.

Substantially linear ethylene interpolymers as used herein are further characterized as having (i) a melt flow ratio, 110/12 > 5.63,

(ii) a molecular weight distribution or polydispersity, Mw/Mn, as determined by gel permeation chromatography and defined by the equation: (Mw/Mn)=(M0/l2)-4.63,

(iii) a critical shear stress at the onset of gross melt fracture, as determined by gas extrusion rheometry, of greater than 4 x 10⁶ dynes/cm³, or a gas extrusion rheology such that the critical shear rate at onset of surface melt fracture for the substantially linear ethylene polymer is at least 50 percent greater than the critical shear rate at the onset of surface melt fracture for a linear ethylene polymer, wherein the substantially linear ethylene polymer and the linear ethylene polymer comprise the same comonomer or comonomers, the linear ethylene polymer has an 12, Mw/Mn and density within 10 percent of the substantially linear ethylene polymer and wherein the respective critical shear rates of the substantially linear ethylene polymer and the linear ethylene polymer are measured at the same melt temperature using a gas extrusion rheometer, and

(iv) a single differential scanning calorimetry, DSC, melting peak between - 30°C and 150°C.

Determination of the critical shear rate and the critical shear stress in regards to melt fracture as well as other rheology properties such as the "rheological processing index" (PI) is performed using a gas extrusion rheometer (GER). The gas extrusion rheometer is described by M. Shida, R.N. Shroff and L.V. Cancio in Polvmer Engineering Science, Vol. 17, No. 11 , p. 770 (1977), and in Rheometers for

Molten Plastics, by John Dealy, published by Van Nostrand Reinhold Co. (1982) on pp. 97-99. The processing index is measured at a temperature of 190°C, at nitrogen pressure of 2500 psig (17 MPa) using a 0.0296 inch (0.0117 cm) diameter, 20:1 LVD die with an entrance angle of 180°. The GER processing index is calculated in millipoise units from the following equation:

PI = 2.15x10^s dynes/cm²/(1000 x shear rate), where: 2.15x10⁶ dynes/cm² is the shear stress at 2500 psi, (17 MPa) and the shear rate is the shear rate at the wall represented by the following equation:

32Q7(60 sec/min)(0.745)(diameter x 2.54 cm/in)³, where Q' is the extrusion rate (g/min), 0.745 is the melt density of the polyethylene (g/cm³), and diameter is the orifice diameter of the capillary (inches).

-7- The PI is the apparent viscosity of a material measured at apparent shear stress of 2.15x10⁶ dyne/cm².

For the substantially linear ethylene interpolymers described herein, the PI is less than or equal to 70 percent of that of a comparative linear olefin polymer having an 12 and Mw/Mn each within 10 percent of the substantially linear ethylene polymers. The rheological behavior of substantially linear ethylene interpolymers can also be characterized by the Dow Rheology Index (DRI), which expresses a polymer's "normalized relaxation time as the result of long chain branching." (See, S. Lai and G.W. Knight "ANTEC '93 Proceedings, INSITE™ Technology Polyolefins (ITP) - New Rules in the Structure/Rheology Relationship of Ethylene/α-Olefin

Copolymers," New Orleans, Louisiana, U.S.A., May 1993.) DRI values range from 0, for polymers which do not have any measurable long chain branching (for example, TAFMER™ products available from Mitsui Petrochemical Industries and EXACT™ products available from Exxon Chemical Company), to 15 and is independent of melt index. In general, for low- to medium-pressure ethylene polymers (particularly at lower densities), DRI provides improved correlations to melt elasticity and high shear flowability relative to correlations of the same attempted with melt flow ratios. For the substantially linear ethylene interpolymers useful in this invention, DRI is preferably at least 0.1 , and especially at least 0.5, and most especially at least 0.8. DRI can be calculated from the equation:

DRI = 3652879 x τ°^{1 00649}/(ηo-1)/10 where τo is the characteristic relaxation time of the material and ηo is the zero shear viscosity of the material. Both τo and are the "best fit" values to the Cross equation, that is, η/ηo = 1/(1+(γ . τ°)ⁿ) where n is the power law index of the material, and η and γ are the measured viscosity and shear rate (rad sec^"1), respectively. Baseline determination of viscosity and shear rate data are obtained using a Rheometric Mechanical Spectrometer

(RMS-800) under dynamic sweep mode from 0.1 to 100 rad/sec at 190°C and a Gas Extrusion Rheometer (GER) at extrusion pressures from 1000 psi to 5000 psi (6.89 to

34.5 MPa), which corresponds to shear stress from 0.086 to 0.43 MPa, using a

0.0754 mm diameter, 20:1 LJD die at 190°C. Specific material determinations can be performed from 140°C to 190°C as required to accommodate melt index variations.

An apparent shear stress versus apparent shear rate plot is used to identify the melt fracture phenomena. According to Ramamurthy in Journal of Rheology, Vol.

-8- 30(2), pp. 337-357, 1986, above a certain critical flow rate, the observed extrudate irregularities may be broadly classified into two main types: surface melt fracture and gross melt fracture.

Surface melt fracture occurs under apparently steady flow conditions and ranges in detail from loss of specular gloss to the more severe form of "sharkskin." In this disclosure, the onset of surface melt fracture (OSMF) is characterized as the beginning of losing extrudate gloss at which the surface roughness of extrudate can only be detected by 40x magnification. The critical shear rate at onset of surface melt fracture for the substantially linear ethylene interpolymers is at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear ethylene interpolymer having about the same 12 and Mw/Mn.

Gross melt fracture occurs at unsteady flow conditions and ranges in detail from regular (alternating rough and smooth or helical) to random distortions. The critical shear rate at onset of surface melt fracture (OSMF) and onset of gross melt fracture (OGMF) will be used herein based on the changes of surface roughness and configurations of the extrudates extruded by a GER.

Substantially linear ethylene interpolymers useful as elastomeric polyolefins of Component C) in the composition of the present invention are also characterized by a single DSC melting peak. The single melting peak is determined using a differential scanning calorimeter standardized with indium and deionized water. The method involves 5 to 7 mg sample sizes, a "first heat" to 150°C which is held for 4 minutes, a cool down at 10°C/minute to -30°C which is held for 3 minutes, and heated at 10°C/minute to 150°C for the "second heat." The single melting peak is taken from the "second heat" heat flow versus temperature curve. Total heat of fusion of the polymer is calculated from the area under the curve.

The term "polydispersity" as used herein is a synonym for the term "molecular weight distribution" which is determined as follows: The polymer or composition samples are analyzed by gel permeation chromatography (GPC) on a Waters 150°C high temperature chromatographic unit equipped with three mixed porosity columns (Polymer Laboratories 103, 104, 105, and 106), operating at a system temperature of 140°C. The solvent is 1 ,2,4-trichlorobenzene, from which 0.3 percent by weight solutions of the samples are prepared for injection. The flow rate is 1.0 milliliters/minute and the injection size is 200 microliters.

The molecular weight determination is deduced by using narrow molecular weight distribution polystyrene standards (from Polymer Laboratories) in conjunction with their elution volumes. The equivalent polymer molecular weights are determined

-9- by using appropriate Mark-Houwink coefficients for polyethylene and polystyrene (as described by Williams and Word in Journal of Polvmer Science. Polvmer Letters. Vol. 6, p. 621 (1968), to derive the following equation:

Mpolyethylene = 0.431 6(M_po|ystyrene)- Weight average molecular weight, Mw, is calculated in the usual manner according to the following formula:

Mw = ∑i wi • Mi, where wi and Mi are the weight fraction and molecular weight, respectively, of the ith fraction eluting from the GPC column.

Additionally the elastomeric polyolefins of Component C) can be extended by incorporation of an aliphatic oil. The extending oils, also referred to as paraffinic/naphthenic oils, are typically fractions of refined petroleum products having less than 30 percent by weight of aromatics (by clay-gel analysis) and having viscosities between 100 and 500 SSU at 100°F (38 °C). Commercial extending oils include SHELLFLEX® oils, numbers 310, 371 and 311 (which is a blend of 310 and 371), available from Shell Oil Company or Drakeol™, numbers 34 or 35, available from Penreco division of Pennzoil Products Company. The amount of extending oil employed varies from 0.01 to 35.0 percent by weight of the elastomeric polyolefin, preferably from 0.1-25 percent.

The elastomeric polyolefin of Component C) may also comprise one or more domain forming rubbery polymers C₂). Such additional rubbery polymers are suitably chosen in order to impart additional impact absorbing properties to the polymer composition. Generally, it is desirable to provide a domain forming rubbery polymer having extremely high melt viscosity, that is, very low melt flow. Such polymers having high melt viscosity are not drawn into extremely thin sections by the shear forces of the compounding process, and retain greater ability to reform discrete rubber particles more closely resembling spherical particles upon discontinuance of shearing forces. Additionally, the domain forming rubbery polymer beneficially should retain sufficient elastic memory to reform droplets in the melt when shearing forces are absent. The domain forming rubbery polymer is selected to be compatible with the elastomeric polyolefin of C) into which it mostly partitions under processing conditions, and therefore, the shearing forces are not as detrimental to the rubber domain. Most preferred domain forming rubbery polymers are those having a melt flow rate, Condition X (315°C, 5.0 Kg) from 0 to 0.5 g/10 min. Representative polymers include block copolymers of styrene and olefin such as styrene-butadiene- styrene (SBS) triblock copolymer and styrene-butadiene diblock copolymer; block

-10- copolymers of styrene and isoprene, such as styrene-isoprene diblock copolymers and hydrogenated versions thereof. Preferably, the block copolymers contain from 15 to 45 weight percent styrene. Most preferably, the block copolymer is a hydrogenated SBS block copolymer. Additionally, an ethylene-styrene interpolymer or another polyolefin as described above can act as the domain forming rubbery polymer.

Generally, higher molecular weight domain forming rubbery block copolymers possess increased melt viscosity. Accordingly, preferred domain forming rubbery block copolymers are those having Mw from 100,000 to 400,000 Daltons, more preferable from 150,000 to 300,000 Daltons, and having Tg less than 25°C, more preferably less than 0°C. Weight average molecular weights recited herein are apparent values based on a polystyrene standard, derived from gel permeation chromatography data, and not corrected for hydrodynamic volume differences between polystyrene and other polymeric Components. Preferred quantities of the domain forming rubbery polymer is from 2 to 40, most preferably 5 to 25 parts by weight per 100 parts of the polyolefin phase of C).

In addition to the domain forming rubbery polymer, a compatibilizing rubbery polymer may also be used in combination with the elastomeric polyolefin of Component C). The desirable characteristic of the compatibilizing rubbery polymer is to provide compatibility between the syndiotactic monovinylidene aromatic polymer, component A), and the elastomeric polyolefin, Component C), so as to minimize interfacial tension between the molten phases and to develop satisfactory adhesion between the solid phases to promote impact adsorption. Decreased interfacial tension in the melt promotes smaller rubber droplet formation due to the driving force to reduce surface area of the rubber particles in contact with the matrix.

Representative compatibilizing polymers include multi-block copolymers of styrene and olefin such as styrene-butadiene-styrene (SBS) triblock copolymer and styrene- butadiene diblock copolymer; block copolymers of styrene and isoprene, such as styrene-isoprene diblock copolymers and hydrogenated versions thereof, and copolymers with greater numbers of blocks such as styrene-ethylene-propylene- styrene copolymers. Preferably, the multi-block copolymers contain from 45 to 80 wt. percent styrene. Most preferably, the block copolymer is a SEPS block copolymer. It is also possible for ethylene-styrene interpolymer to act as the compatibilizing rubbery polymer. Component C can also be any substantially random interpolymer of a vinyl aromatic and an aliphatic alpha-olefin monomer. The term "interpolymer" as used

-11- 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 ethylene CH₂=CH₂, the derivative of this unit as incorporated in the polymer is -CH₂-CH₂-. The vinyl aromatic monomers contained in the interpolymers used as

Component C) include those vinyl aromatic monomers described previously as monomers useful for preparing the syndiotactic monovinylidene aromatic polymers of Component A).

The aliphatic alpha-olefin monomers contained in the interpolymers used as Component C) 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 ethylene or propylene, preferably ethylene, optionally together with one or more other alpha-olefins having from 3 to 8 carbon atoms, such as for example ethylene and propylene, or ethylene and octene, or ethylene and propylene and octene.

The interpolymers suitable as Component C) 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-0416815. A particular distinguishing feature of pseudo-random interpolymers is the fact that all phenyl or substituted phenyl groups substituted on the polymer backbone are separated by two or more methylene units. In other words, the pseudo-random interpolymers comprising an a-olefin and vinyl aromatic monomer can be described by the following general formula (using styrene as the hindered monomer and ethylene as the olefin for illustration):

CH₂ - CH₂ — CH — CH ^ CHN CH ^

-12- where j, k and I > 1

The symbol > means equal to or greater than

It is believed that during the addition polymerization reaction of ethylene and styrene employing a catalyst as described hereinafter, if a hindered monomer (styrene) is inserted into the growing polymer chain, the next monomer inserted must be ethylene or a hindered monomer which is inserted in an inverted fashion. Ethylene, on the other hand, may be inserted at any time. After an inverted hindered monomer insertion, the next monomer must be ethylene, as the insertion of another hindered monomer at this point would place the hindering substituent too close to the previously inserted hindered monomer.

Most preferably, Component C) is a pseudo-random linear interpolymer comprising ethylene and styrene.

The content of units derived from the vinyl aromatic monomer incorporated in

Component C), and preferably in the pseudo-random, linear interpolymer, preferably is greater than 40 wt. percent, more preferably at least 50 wt. percent, and most preferably at least 60 wt. percent based on the total weight of the interpolymer.

Preferably, the interpolymer used as Component C) has a weight average molecular weight (Mw) of greater than 13,000. Also preferably such polymers possess a melt index (12), ASTM D-1238 Procedure A, condition E, of less than 125, more preferably from 0.01 - 100, even more preferably from 0.01 to 25, and most preferably from 0.05 to 6.

While preparing the substantially random interpolymer which can be used as

Component C), as will be described hereinafter, an amount of atactic monovinylidene aromatic homopolymer may be formed due to homopolymerization of the vinyl aromatic monomer at elevated temperatures. In general, the higher the polymerization temperature, the higher the amount of homopolymer formed. The presence of monovinylidene aromatic homopolymer is in general, not detrimental for the purposes of the present invention and may be tolerated. The monovinylidene aromatic homopolymer may be separated from Component C), if desired, such as by extraction with a suitable extracting agent, acetone or chloroform. For the purpose of the present invention it is preferred that Component C) contain no more than 20 percent by weight, based on the weight of Component C), more preferably less than 15 weight percent of monovinylidene aromatic homopolymer.

The substantially random interpolymers used as Component C) 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

-13- will not be substantially affected. The polymers may be readily sulfonated or chlorinated to provide functionalized derivatives according to established techniques. The interpolymers may also be oil extended or combined with other lubricants.

The pseudo-random interpolymers used as Component C) can be prepared as described in EP-A-0416815. 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-0416815; EP-A-0468651 ; EP-A-0514828; EP-A-0520732; WO 93/23412, U.S. Application Serial No. 34,434, filed March 19, 1993, U.S. Application Serial No. 82,197, filed June 24, 1993, as well as U.S. Patents: 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.

Block copolymers of styrene and olefin can also be used as Component C). Such block copolymers include copolymers of styrene and diene monomers such as styrene-butadiene-styrene (SBS) triblock copolymer and styrene-butadiene diblock copolymer; block copolymers of styrene and isoprene, such as styrene-isoprene diblock copolymers and hydrogenated versions thereof. Preferably, the block copolymers contain from 15 to 45 weight percent styrene. Most preferably, the block copolymer is a hydrogenated SEBS block copolymer. Most preferred domain forming rubbery polymers are those having a melt flow rate, Condition X (315°C, 5.0 Kg) from 0 to 0.5 g/10 min. The preferred rubbery block copolymers are those having Mw from 100,000 to 400,000 Daltons, more preferable from 150,000 to 300,000 Daltons, and having rubbery phase Tg less than 25°C, more preferably less than 0°C. Weight average molecular weights recited herein are apparent values based on a polystyrene standard, derived from gel permeation chromatography data, and not corrected for hydrodynamic volume differences between polystyrene and other polymeric components.

The composition of the present invention can also comprise from 0 to 10 wt. percent of a lubricant, Component D), based on the total weight of the composition. Exemplary lubricants include stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene 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, palmityl palmitate, butylene glycol montanate (Wax OP available from Hoechst Celanese), pentaerythritol tetramontanate (TPET 141 available from

-14- Hoechst Celanese), aluminum mono-stearate, aluminum di-stearate, montanic acid wax, montanic acid ester wax, polar polyethylene waxes, and non-polar polyethylene waxes.

Nucleators may also be used in the present invention and are compounds capable of reducing the time required for onset of crystallization of the syndiotactic vinylaromatic 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. In some cases, Component B), the wollastonite, may function as a nucleator. Especially preferred compounds are aluminum and sodium salts of benzoic acid and C_MO 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, 565, 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

-15- 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-butylphenyl-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 organopolysiioxane or mineral oil; blowing agents, extrusion aids, stabilizers such as bis(2,4-di- tertbutylphenyl)pentaerythritol and tris nonyl phenyl phosphite.

The compositions of the present invention are prepared by combining the respective components under conditions to provide uniform dispersal of the ingredients. For best results, the polymer(s) and all additives except calcium silicate are usually melt mixed under harsh mixing conditions to maximize dispersion and distribution of ingredients. The calcium silicate is then added to the melt mixture under gentler mixing conditions to allow dispersion without causing attrition of the reinforcing agent. Mechanical mixing devices such as extruders, internal mixers, continuous mixers, ribbon blenders, solution blending or any other suitable device or technique may be utilized.

The composition of the present invention can produce molded articles having improved mechanical and thermal performance, very good surface smoothness, and excellent thermal aging stability. This combination of properties is required in such applications as automotive light housings.

The operating conditions for molding compositions which include Component C) are preferably chosen such that the preferred rubber particle morphology occurs. This morphology is generally spherical in nature. If the molten polymer, containing undesirable thin strata of the olefinic impact modifier due to shearing forces, is quenched relatively quickly from the melt, the necessary droplet formation cannot occur and the resulting molded part will be deficient in impact properties. This result can occur, for example, in a molding process using molds operating at too low a mold temperature.

-16- 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 per hundred or weight percentages unless otherwise indicated. The compositions in TABLE I are made using the following procedure:

All ingredients except the calcium silicate filler are dry mixed and melt compounded on a corotating twin screw extruder operating with a nominal 300°C barrel temperature. The twin screw extruder is configured with two mixing zones, wherein the ingredients are melted and/or mixed in the first mixing zone. The calcium silicate filler is introduced into the extruder in the second mixing zone and mixed with the melt mixture which is formed into pellets. The compounded pellets are injection molded into ASTM Type I tensile bars and 2.5" diameter disks using a 290°C barrel temperature and 149°C mold temperature.

The aging stability is determined by measuring the weight loss of samples which are aged in a circulating air oven for 168 hours at 220°C. Tensile and flexural properties are measured according to ASTM D638 and ASTM D790, respectively. Deflection temperature under load (DTUL) is measured according to ASTM D 648.

-17- The 60° Gardner Gloss is measured according to ASTM D-523.RAW MATERIALS Component A: QUESTRA™ F2250, a Syndiotactic Polystyrene (SPS)

(Mw=250,000) manufactured by the Dow Chemical Company Component B: RRIMGLOS™ 1 , an untreated wollastonite RRIMGLOS™ 1-10734, a wollastonite surface treated with silane coupling agent

RRIMGLOS™ 1-10013, a wollastonite surface treated with amino coupling agent

RRIMGLOS™ l-EPOXY, a wollastonite surface treated with epoxy coupling agent

10 WOLLASTOCOAT™-10734, a wollastonite surface treated with silane coupling agent

400 WOLLASTOCOAT™- 1-10734, a wollastonite surface treated with silane coupling agent. All wollastonites are from NYCO Corporation.

Component C: Kraton™ G 1651 (a hydrogenated SEBS block copolymer manufactured by The Shell Chemical Company) Component D: Hoescht Wax OP™, a butylene glycol montanate wax from

Hoescht Celanese Antioxidants: Ultranox™ 815A from GE Specialty Chemicals and Irganox™

565 and 1010 from Ciba-Geigy Nucleator: aluminum tris(p-tert-butyl)benzoate (pTBBA-AI)

Comparative Inorganic Filler: MP 10-52, talc from Specialty Mineral Corporation and aluminum borate whiskers is Alborex Y available from Shikoku Chemicals (9AI2O32B2O3).

Black Pearls 880 concentrate is a colorant additive containing 25 percent carbon black and 75 percent SPS.

-18- COMPONENT(wt. percent) !* II III IV V VI VII VIII

A) SPS 73.8 73.2 73.2 73.2 63.2 73.2 73.2 73.2

B) RRIMGLOS 1 0 20 0 0 0 0 0 0

B) RRIMGLOS 1 -10734 0 0 20 0 30 0 0 0

B) RRIMGLOS I -10013 0 0 0 20 0 0 0 0

B ) RRIMGLOS 1-EPOXY 0 0 0 0 0 0 0 20

B) 10 WOLLASTOCOAT- 0 0 0 0 0 20 0 0 10734

B) 400 WOLLASTOCOAT- 0 0 0 0 0 0 20 0 10734

D) Hoechst Wax OP 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

E) Kraton G1651 5 5 5 5 5 5 5 5 pTBBA-AI (nucleator) 0 0.6 0.6 0.6 0.6 0.6 0.6 0.6

Ultranox 815A(additive) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

Irganox 565(additive) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Talc (filler) 20 0 0 0 0 0 0 0

FEEDABILITY DURING EASY HARD EASY HARD EASY EASY EASY HARD COMPOUNDING

PROPERTIES

T-bar total weight loss 24.8 10.8 12.7 10.6 5.9 21.1 21.6 9.1 (percent) at 220 °C in air for 168 hr.

Gardner gloss at 60 degree 100 101 98 99 96 100 100 101 flex modulus (MPa) 5419 6026 6688 6136 7584 4757 4481 6832

flex strength (MPa) 73.1 83.6 86.5 69.6 90.3 69.6 66.1 88.0

tensile elongation at yield 0.7 0.8 0.8 1.2 0.9 1.3 1.4 0.8 (percent) tensile strength (MPa) 39.5 47.6 50.7 55.7 60.0 46.1 42.4 49.7

DTUL @ 264 psi (°C) 102 104 106 103 116 93 96 105

Comparative example

The data in the above table indicates the wollastonite samples had better thermal performance and mechanical properties than the talc comparative example. All examples had excellent surface smoothness as determined by 60° Gardner Gloss.

-19- The surprising improvement in thermal aging stability is also demonstrated. The wollastonites with silane surface treatment is easier to feed during compounding. The following examples are prepared as in examples l-VIII.

Materials IX X^* (wt. percent) (wt. percent)

SPS 71.5 71.5

Kraton G1651 5.0 5.0

Irganox 1010 1.0 1.0

Black Pearls 880 cone. 2.5 2.5

Al Borate 20

RRIMGLOS I 20

Aging Aging

Temperature Time weight loss weight loss

(°C) (hours) (percent) (percent)

180 500 .96 1.54

190 500 8.91 13.17

200 300 11.98 16.10

Comparative Example

The formulations comprising wollastonite have significantly and surprisingly better thermal stability than the formulations with Al Borate.

-20-

Claims

WHAT IS CLAIMED IS:

I . A composition comprising:

A) a syndiotactic monovinylidene aromatic polymer, and

B) a calcium silicate filler.

2. The composition of Claim 1 wherein the syndiotactic monovinylidene aromatic polymer is a syndiotactic polystyrene.

3. The composition of Claim 1 wherein the calcium silicate filler is of the formula CaO Si0₂.

4. The composition of Claim 3 wherein the filler is wollastonite.

5. The composition of Claim 3 wherein the filler is zonotolite.

6. The composition of Claim 1 wherein the calcium silicate filler is coated with a surface coating of a sizing agent selected from the group consisting of silane, amino, or epoxy based sizing agents.

7. The composition of Claim 1 wherein the syndiotactic monovinylidene aromatic polymer is present in an amount of from 60 to 95 weight percent based on the total weight of the composition.

8. The composition of Claim 1 wherein the calcium silicate filler is present in an amount of from 10 to 35 weight percent based on the total weight of the composition.

9. The composition of Claim 1 which additionally comprises a ductility modifier.

10. The composition of Claim 9 wherein the ductility modifier is an elastomeric polyolefin.

I I . The composition of Claim 9 which additionally comprises a domain forming rubbery polymer.

12. The composition of Claim 1 1 wherein the domain forming rubber polymer is a styrene/ethylene-propylene/styrene block copolymer.

13. The composition of Claim 1 which also comprises a lubricant.

14. The composition of Claim 1 which also comprises a nucleator.

15. Molded articles produced from the composition of Claim 1.

-21-