Syndiotactic vinyl 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 cast-tenter films and fibers, the melt strength is insufficient at processing temperatures to obtain desired properties.

Syndiotactic copolymers have also been developed having superior heat and chemical resistance. U.S. 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 films, but instead utilizes a solution casting process which is slow and has the added problem of solvent removal.

Films have been produced from linear syndiotactic vinyl aromatic polymers as described in U.S. 5,166,238, U.S. 5,093,758 and U.S. 5,188,930. However, films produced from linear syndiotactic vinyl aromatic polymers are known to have poor tear strength during manufacture and in applications.

Therefore, it would be useful to obtain a syndiotactic vinyl aromatic polymer, having good heat and chemical resistance, which is melt processable at high temperatures while maintaining good melt strength such that films having good tear strength can be obtained therefrom.

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

The films of the present invention have improved melt and tear strength.

In one embodiment, the present invention is a film prepared from a composition comprising a long chain branched syndiotactic vinyl 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 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, 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 vinylaromatic 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-vinyl toluene copolymers.

Syndiotactic vinyl 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, included herein by reference.

Syndiotactic polystyrene is the currently preferred syndiotactic vinyl 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 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):

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, 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 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 vinyl 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 vinyl aromatic polymers are well known in the art and are described in US-A-4,680,353, 5,066,741, 5,206,197 and 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 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.

Typically, the films of the present invention are produced from a composition of a LCB-SVA polymer without the presence of other polymers. However, films 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 films 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 films, 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 nylonS, nylon-6,6; polyesters, such as poly(ethylene terephthalate), poly(butylene terephthalate); and copolymers or blends thereof. Other materials or additives, including antioxidants, antiblock agents such as fine particles of alumina, silica, aluminosilicate, calcium carbonate, calcium phosphate, and silicon resins; impact modifiers, ignition resistant agents, coupling agents, for example maleated polymers, including maleic anhydride modified polyphenylene oxide, or maleic anhydride modified syndiotactic vinylaromatic polymers, binders to improve the wet strength of a base fabric, flame retardants including brominated polystyrene, brominated syndiotactic vinylaromatic polymers, antimony trioxide, and polytetrafluoroethylene may be added to the LCB- SVA polymer composition, the films or articles made therefrom.

The films of the present invention can be obtained as a monolayer film or a multilayer film structure. Typically, the films of the present invention are from approximately 1 , to 10 mils thick, however, thicknesses of up to 50 mils can be obtained. Additionally, a film sheet can be obtained which can have thicknesses of up to 125 mils.

The films of the present invention can be made by various processes including blowing film and cast/tentering. Typically cast/tentering is used wherein the LCB-SVA polymer is heated in a melt extruder and transferred to a vertical die wherein the molten polymer is deposited in the form of a continuous sheet or web on a large cylinder or casting drum, orientated, stretched as is well known in the art.

The films of the present invention can also be coated or laminated with other films or coatings to add additional properties to the film.

The films of the present invention can be used in optical magnetic media, electrical, packaging, release film, automotive and construction applications.

The following examples are provided to iliustrate 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 EXAMPLE 1-PRODUCTION OF LCB-SPS 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 is prepared following the procedure described in J. Polymer Sci., Part A, Polymer Chem., 32 (1994) 2023 by W.H. Li, et al.

Polymerization is 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 67.50C. Octahydrofluorenyl titanium trimethoxide catalyst (.007 M) with necessary amounts of methylalumoxane and triisobutylaluminum 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: Sample ppm DSE Mw 1 Mn Mz MwJMn 1 400 294,900 82,100 1,151,900 3.59 2 400 334,800 86,500 1,377,300 3.87 3 250 420,000 92,300 2,418,300 4.55 4 250 368,900 71,600 1,962,000 5.15

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: Sample Mw Mn Mz Mw/Mn 1 279,900 75,000 1,137,400 3.73 2 304,900 82,000 0 1,161,100 0 3.72 3 313,000 74,900 1,294,900 4.18 4 301,000 65,000 1,204,900 4.63 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: Sample Melt strength(g) MFR (g/10 min.) 1 4.0 19.1 2 5.4 14.4 3 5.5 15.5 4 4.5 17.1 Control 1.9 3.6 The LCB-SPS samples have higher melt strengths and higher melt flow rates than the linear SPS control sample.

EXAMPLE 2 PREPARATION OF LCB-SPS AND FILM SHEET 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 cataiyst 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 devolatiiized and pelletized as described previously. The molecular weight of the polymer is determined via high temperature size exciusion chromatography and the results are shown below: Mz Mw Mn Mz Mz 11 Mw/Mn 284,000 61,400 1,049,500 2,178,900 4.63 A 300,000 Mw linear SPS polymer is used as a control.

The LCB-SPS and linear SPS polymers are converted to film sheets using the following process: The resin pellets are fed into a 1 inch Killion single-screw extruder at 300"C, extruded through a slit die, and quenched in a casting drum at 88"C to produce 1 0-mil-thick (250 microns) sheets. The sheets are simultaneously, biaxially stretched in an Iwamoto BIX-703 stretcher to become 1 -mil(25 micron)films under the following stretching conditions, stretching temperature of 110°C, sample preheating time of 2 minutes, stretching rate of 1200 percent/min. and a stretch ratio of 3.5 by 3.5. Twenty percent of the linear SPS films break during film stretching, while none of the LCB-SPS films break under the same stretching conditions. The films produced are annealed with film edges adhered on a metal frame, in an oven at 220"C for 1 minute.

Tear strengths of the films are measured according to ASTM D1938. The average tear strength of the LCB-SPS film is 2.67 g/mil, which is 44 percent higher than the 1.86 g/mil of the linear SPS film.