BACKGROUND OF THE INVENTION Syndiotactic polystyrene is a commercially important material useful in the preparation of articles and objects having an extremely high resistance to deformation due to the effects of temperature. The polymers have vers high melting points and low solubilit in organic solvents. due to a stereoregular <BR> <BR> <BR> <BR> structure, composed of phenyl groups alternating regularly from side to side of the chain.

Transition metal complexes have been used as Ziegler-Natta catalysts for the polymerization of olefins, including stereospecific polymerizations.

For example. Group 4 half-sandwich complexes, such as titanocene. zirconocene or hafnocene derivatives, activated svith meth-l aluminoxane (MAO) are efficient homogeneous catalysts for the promotion of syndioselective polymerization of styrene. More recently, metal complexes of composition CPML,'I-A-, where Cp is substituted or unsubstituted cyclopentadienyl. M is a transition mental. L is an anionic ligand. and A is a noncoordinating compatible anion of a Bronsted acid salt, for example tetraphenyl borate, are have been used for syndiotactic polymerization of styrene. Formation of these metal-borate complexes requires an additional step in the polymerization process, however, and therefore increases production costs. A need exists for methylaluminoxane cocatalysts which do not require the preformation of the metal-borate complex, and which produce syndiotactic polystyrene in high yield.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide materials which can be cocatalysts X-ith methylaluminoxane. xvithout additional components. for the sydiotactic polymerization of styrene. It is a further object to provide for a two-step synthesis of the cocatalyst from commercially available starting materials, in high yield, without the need for purification of the product.

In one aspect, the invention relates to a composition of formula R¹M(R²)n(N(SO2CF3)2)3-n, wherein M is Ti, or Zr; R¹ is indenyl, cyclopentadienyl or pentamethylcyclopentadienyl, R² is independently indenyl, cyclopentadienyl, pentamethylcyclopentadienyl, methyl, methoxy, hydroxy, 2,4,6-trimethylphenoxy, trifluoroethoxy, hexafluoroisopropoxy, or chloro, and n=1 or 2. Preferably, n = 2 and M = Ti. More preferably, R² = cyclopentadienyl or methoxy, n = 2 and M = Ti.

In another aspect, the invention relates to a process for the production of the metal triflamides described above, comprising reacting AgN (SO2CF3) 2 with R¹R²MCl2 in a suitable solvent. and removing thesolvent.

In yet dnother aspect, the invention relates to a process for the production of highly syndiotactic polystyrene. comprising premixing the composition described above with methylaluminoxane and combining the catalyst premix with styrene, at a temperature of 25-100 ° C. Preferably, the molar ratios of styrene, methylaluminoxane and metal triflamide complex are 6000/400-600/0.5-2. The process may additionally comprise a solvent.

DETAILED DESCRIPTION OF THE RTVENTION 'Syndiotactic"as used herein refers to polysryrene having a stereoregular structure of greater than 800/'o as determined by extraction with methvl ethyl ketone (MEK). The weiCht of syndiotactic polystyrene is obtained from the MEK-insoluble portion and that of atactic polystyrene from the soluble fraction. The polymer tacticity may be confirmed by IR spectroscopy.

The compositions of the invention are described by the formula R'M (R²)n(NTf2)3-n, wherein M is Ti. or Zr; Tf is SO, CF-,. R'is indenyl, cyclopentadienyl (Cp) or pentamethyl cyclopentadienyl (Cp*), R2 is independently indenyl, cyclopentadienyl, pentamethylcyclopentadienyl, methe l, methoxy, hydroxy, 2, 4. 6-trimethylphenox !. trifluoroethoxy. hexafluoroisopropoxy, or chloro, and n=1 or 2. Preferred substituents for R 2 are cvclopentadienyl and methoxy. A preferred metal M is titanium.

The triflamide complexes of the invention may be prepared bu-té rection of one or two equivalents of AgNTf2 with complexes R'R-'MCI,, where R¹ and R² are as defined above. For R', R2 = Cp, M=Ti, and n=2, starting material Cp2TiCl2 is commercially available from Aldrich Chemical Co. For R'= Cp and M=Ti, starting material CpTiCl3 is commercially available. For R'= Cp*, the starting material Cp*MCl3 can be prepared according to the procedure of Threlkel. et al., J. Organometal. Chem.. 1977,1.

The Cp*M R²Cl2 complexes are prepared by the rection of an excess of the corresponding R2H compound with Cp*MCl3. The zirconium and silver metal complexes may also be prepared by these same rections.

Rection of the dichloride complexes N ith one equivalent of AgNTf2 gives the mono-triflamide complexes of the invention; with two equivalents of AgNTf2, the bis-triflamides are produced. AgNTf2 is prepared from the lithium salt LiNTf, obtained from the 3M Corporalion. through the imide.

The rection may be conducted at temperatures of 0-50°C. preferably at about 25°C. for a time sufficient to fulls react the tartina materials. Typical rection times are about ts-o hours. Light should be excluded from the rection. The product may be isolated by removal of the solvent under vacuum, extraction of the residue into toluene and evaporation of the toluene under vacuum. The hydroxy complex may be prepared bu-té rection of the corresponding triflamide complet. where R'-is meth-l. w-ith one equin-alent of water in diethyl ether.

The metal triflamide complexes of the invention may be used as cocatalysts with methylaluminoxane for the syndiotactic polymerization of styrene. Methylaluminoxane (hereinafter MAO) may be prepared according to any known technique, including, for example. the rection of trimethylalluminum and a hydrate metal salt as taught by U. S. Patent No.

4,544,762, and is commercially available. For purposes of calculating the molar ratio of MAO to metal triflamide cocatalyst, MAO is assigne a repeating unit structure corresponding to the formula-Al (CH ;) O- with a unit molecular weight of 100.03.

The triflamides are normally combine with MAO in the presence of an aliphatic, cycloaliphatic or aromatic solvent or a combination of such solvents. The components are employed in quantities which provide an atomic ratio of A1: M suitably from about 10: 1 to about 50,000: 1, more suitably from about 50: 1 to about 10,00: 1, most suitably from about 100: 1 to about 1000: 1.

The cocatalysts may be combine in any order in an inert atmosphere such as nitrogen, argon, xenon, or combinations thereof The components are mixed at any suitable temperature, preferably from about 0°C to about 50°C, more suitably about 25°C.

The polvmerization is conducted at temperatures of from about 25'C to about 100°C. preferably from about 30°C to about 60-C, for a time sufficient to produce the desired polymer Ts pical reaction times are from several minutes to several hours. commonly from about one to ten hours. The optimum time will våry depending on the temperature. solvent, and other rection conditions employed.

The polymerization can be conducted at subatmospheric pressure as ,, N-ell as superatmospheric pressure. It is preferred that near atmospheric pressure be employed.

The polymerization is normally conducted in the presence of an inert solvent as a diluent. Examples include aliphatic, cycloaliphatic, aromatic. and halogenated aromatic hydrocarbons. as well as-mixtures thereof. Preferred solvents are linear and branched C4to C20 alkanes, toluene, and mixtures thereof. Suitable amounts of solvent are employed to provide a monomer concentration from about 5% to about 100% by weight.

Purification of the resulting polvmer to remove entrained catalx st may be desired. The presence of entrained catalyst may be determined from ash residues from pyrolysis of the polymer that are attributable to aluminum and titanium values. A suitable technique for removing such compound is solvent extraction utilizing hot, high boiling chlorinated solvents, followed by filtration.

EXAMPLES Example 1: Cp2Ti(N(SO2CF3)2)2 (I) AgN(SO2CF3)2. The imide HN(SO2CF3)2 was obtained from the lithium salt. LiN(SO2CF3)2(10g, 35 mmole) was added to 50mL concentrated sulfuric acid. The free imide was distille at about 90°C, 10 mm Hg and purified by sublimation at about 70°C, 1-2 mm Hg giving 7.4 g (74%) HN(SO2CF3)2. The silver salt was then obtained from the imide. Ag2CO3(2.0 a. 0. 2 mmol) was added slowly to a stirring solution of HN (SO2CFF. Sg.

12.0 mmole) in 25 mL water. The mixture was then digeste, wrapped in foil. at 60°C for 1 h and the excess Ac,, CO3 filtered off. The water was removed under vacuum giving white powder of AgNTTf,. Dissolution of the powder in diethyl ether (25 mL) followed by filtration and removal of all volatiles under vacuum gave 4.6g (95%) of white AgNTf2.

A solution of AgNTf, (0.140g, 0.361 mmole) in 5 mL diethvl ether was added to a stirring slurry of Cp2TiCl2(0.045g, 0.18 mmole) in 7 mL diethyl ether. After stirring at room temperatuie for 3h (wrapped in foil), the mixture was filtered and all volatiles removed in vacuo-giving a yellow-brown oil. The oil was washed with pentane and extracted with toluene (5 mL).

Removal of the solvent under vacuum gave 0.076g (57%) of I as an orange residue.

Example 2: Cp*Ti(OCH3)(NTf2)2 (II) Cp*Ti(OCH3)Cl2.(OCH3)Cl2. Cp*TiCl3(0.200 g, 0.691 mmol) was weighed into a 50 ml Schlenk flask and 2.0 ml methanol was added. The solution was refluxed for one hour, then cooled to room temperature and then in an ice bath.

Orange crystals slowly formed. The mother liquor was syringe out. and the crystals were dried under vacuum.

A solution of AgNTf2(0.123 g, 0.316 mmole) in 5 mL diethyl ether was added to a stilTino solution of Cp*TiCl2(OCH3)(0.0.045g, 0.16 mmole) in 5 mL diethyl ether. After stirring at room temperature for 2 h (RxTapped in foil). the mixture xvas filtered and all volatiles removed in vacuo gain-in a red orange oit The oil was washed w-ith pentane and extracted xvith toluene (5 mL). Removal of the toluene under vacuum gave 0.1 1 0g (90%) 11 as red orange residue.

Example 3: Svndiotactic Polvmerizations of Stvrene with MAO A stNIrene: Al: catalyst ratio of 6000: 500 : 1 was effected cafter U. S.

Patent No. 5,045,517. Into one 100 mL Schlenk flask were added 0.0- g (0.07 mmol) Cp=Ti (lTf,), catalyst and 5 mL toluene, and into another, 4. 2 mL of a 10% solution (3.7 mmol) of MAO in toluene and toluene (5 mL). The mixtures were combine, stirred for 15 minutes at room temperature and then transferred to an oil bath at 50°C. Styrene (5.0 mL, 44 immoles) was added.

The mixture was allowed to stir for 3 hours and was quenched by the addition of 20 mL of methanol. The mixture was poured into 50mL of 3% HCl in methanol. was diluted with additional methanol to the 200 mL mark and was stirred for 1 hour. The precipitated polystyrene (PS) was separated bs- filtration and was weighed after draina in a 100°C vacuum oven for 24 hours.

Both the insoluble portion and the soluble fraction (reprecipitated from methanol) were again dried at 100°C in vacuo for 24 hours. The weight of syndiotactic polystyrene (SPS) was obtained from the 2-butanone-insoluble portion and that of atactic polystyrene (APS) from the soluble fraction. The polymer obtained was 93% syndiotactic polystyrene. The polymer tacticity was confirme by IR spectroscopy.