Improved catalyst composition for preparing high-syndiotacticity polystyrene from styrene or other aryl ethylene monomers and processes using the same

Abstract: A catalyst composition for preparing high-syndiotacticity polystyrene polymers which comprises: (a) a titanium complex represented by the following formula of TiR' 1 R' 2 R' 3 R' 4 or TiR' 1 R' 2 R' 3 , wherein R' 1 , R' 2 , R' 3 and R' 4 are, independently, an alkyl group, an aryl group, and alkoxy group, an aryloxy group, an amino group, a hydrogen atom, or a halogen atom; (b) a cyclopentadienyl complex of silicon (Si), germanium (Ge), or tin (Sn) represented by one of the following formulae wherein R 1 , R 2 , R 3 and R 4 are, independently, an alkyl group, an aryl group, a silyl group, a germanyl group, a stannyl group, or a halogen atom; R is an alkyl group, aryl group, a hydrogen atom, or a halogen element; and X can be one of the Group IVA elements of silicon (Si), germanium (Ge) or tin (Sn); and (c) an activated transitional metal co-catalyst which can be methyl aluminoxane, or a mixture containing a non-coordinated Lewis acid (a Lewis acid is an electron-pair donor) and a trialkyl aluminum, such as triethyl aluminum or tetraisobutyl aluminum.

Description: FIELD OF THE INVENTION The present invention relates to an improved catalyst composition for preparing high-syndiotacticity polystyrene polymers. More specifically, the present invention relates to an improved catalyst composition for preparing polystyrene polymers which provides high activity and high syndiotacticity, and with a lowered cost. BACKGROUND OF THE INVENTION Peroxide is the most commonly used catalyst in the polymerization of polystyrene which causes free radicals to be generated to initiate the polymerization reaction. The polystyrene produced from the peroxide-catalyzed processes belongs to the type of atactic polystyrene (aps), which, by definition, does not possess any stereo regularity. Atactic polystyrene, which has been widely used in many commercial applications for more half century, is an amorphous polymer. The amorphous physical characteristics of atactic polystyrene have limited the range of its application. Atactic polystyrene is primarily used in a relatively low-value added market, and it typically cannot be used in engineering plastics applications. Isotactic polystyrene (ips), on the other hand, was also developed as early as 1955, by G. Natta using the co-called Ziegler-Natta catalyst. Isotactic polystyrene is a highly crystalline polymer and it exhibits a very high melting point (240 °C). These properties make the isotactic polystyrene a suitable candidate for many engineering plastics applications. However, the isotactic polystyrene suffers from the problem of having an undesirably low crystallization rate, thus causing fabrication difficulties. Unless this problem can be overcome, the isotactic polystyrene does not appear to have very high commercial potential. Relative to atactic polystyrene and isotactic polystyrene, the syndiotactic polystyrene was a late comer. It was not until 1986 when the syndiotactic polystyrene was first developed by Ishihara using a metallocene catalyst composition. Typically, the polymerization of syndiotactic polystyrene requires a catalyst composition containing a transitional metal titanium complex and methyl aluminoxane (or "MAO"). The concerted actions of the titanium complex and the methyl aluminoxane allows syndiotactic polystyrene to be polymerized. Descriptions of the processes for preparing syndiotactic polystyrene have been provided in, for example, EP-A-0 210,615, in which a catalyst composition containing tetra(ethyoxy)titanium and methyl aluminoxane was used for preparing syndiotactic polystyrene; and in world patent application WO 8,810,275, in which high syndiotacticity polystyrene was reported to have been prepared using a catalyst composition containing cyclopentadienyl trichlorotitanium and methyl aluminoxane. U.S. Pat. Nos. 4,774,301 and 4,808,680 disclosed the use of a catalyst composition containing a transitional metal zirconium complex and methyl aluminoxane for preparing syndiotactic polystyrene. Compared to the catalyst compositions using a titanium complex and methyl aluminoxane, these catalyst compositions containing the zirconium complex exhibited noticeably lower activity, and the polystyrene so produced exhibited relatively lower molecular weight and a lower degree of syndiotacticity. All of the catalyst compositions described above for preparing syndiotactic polystyrene contain Group IV transitional metal complexes and methyl aluminoxane to provide activation. It should be noted that a very high excess of methyl aluminoxane is required to provide the desired activated catalyst. Because of the high cost of methyl aluminoxane, these processes have very limited commercial applications. Thus it is highly desirable to develop a metallocene based catalyst composition which can minimize, or even eliminate, the amount of methyl aluminoxane required. EP-A-0 505,890 and World Patent Application WO 930,367 disclosed a catalyst composition which contains cyclopentadienyl trialkyl titanium as a catalyst, a non-coordinated Lewis acid as a co-catalyst, and triisobutyl aluminium as a scavenger, for the preparation of high syndiotactic polystyrene. These catalyst compositions, however, have relatively low activity. Within the family of titanium complexes, or more specifically titanocenes, the catalytic activity, for polymerizing polystyrene, is higher for titanocenes containing one cyclopentadienyl ligand than those titanocenes containing two cyclopentadienyl ligands. The catalytic activity of the titanocene containing one cyclopentadienyl ligand is also higher than that of titanium complexes containing no cyclopentadienyl ligand (which are thus by definition not titanocenes). This relative relationship has been disclosed in EP-A-0 210,615. While the catalytic activity of the titanium complexes containing no cyclopentadienyl ligand is substantially lower than that of the titanocene containing one cyclopentadienyl ligand, it has the advantage of being substantially cheaper. Therefore, from economic considerations, it is highly desirable to develop a co-catalyst composition that can substantially increase the activity of the cheapest titanium complexes, that is, the titanium complexes that contain no cyclopentadienyl ligand, so as to lower the overall cost of the metallocene catalyst composition while providing excellent catalytic activity. SUMMARY OF THE INVENTION The primary object of the present invention is to develop an improved catalyst composition for preparing high-syndiotacticity polystyrene polymers or other aryl ethylene polymers from styrene or substituted styrene wherein the substituted styrene is a C 1-12 substituted styrene or a mono- or poly-halogenated styrene. More specifically, the primary object of the present invention is to develop an improved catalyst composition for preparing polystyrene polymers which allows the use of more economic ingredients and minimizes the expensive components such as methyl aluminoxane, so as to substantially lower cost of the catalyst composition, while providing high catalytic activity and high syndiotacticity. The catalyst composition according to the present invention comprises the following three main components: (a) 0.1 to 10 parts by mole of a titanium (IV) or titanium (III) complex which does not contain cyclopentadienyl ligand, represented by the following formula of TiR' 1 R' 2 R' 3 R' 4 or TiR' 1 R' 2 R' 3 , wherein each of said R' 1 , R' 2 , R' 3 and R' 4 is, independently, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an amino group, or a halogen atom; (b) 0.1 to 10 parts by mole of a cyclopentadienyl complex of silicon (Si), germanium (Ge), or tin (Sn) represented by one of the following formulae wherein each of said R 1 , R 2 , R 3 and R 4 is, independently, an alkyl group, an aryl group, a silyl group, a germanyl group, a stannyl group, or a halogen atom; R is an alkyl group, an aryl group, a hydrogen atom or a halogen atom; and X is selected from the group consisting of silicon (Si), germanium (Ge) and tin (Sn); and (c) an activated transitional metal co-catalyst, which is either a methyl aluminoxane (20 to 10,000 parts by mole), or a mixture containing 0.1 to 20 parts by mole of a non-coordinated Lewis acid (preferably a borate, such as N,N-dimethyl anilinium tetrakis (pentafluorophenyl) borate, triphenyl carbonium tetrakis(penta-fluorophenyl)borate, and dialkyl ferrocenium tetrakis(pentafluorophenyl) borate) and 100 to 10,000 parts by mole of a trialkyl aluminium such as trimethyl aluminium triethyl aluminium, triisobutyl aluminium tri(n-butyl)aluminium, tri(n-propyl)aluminium or triisopropyl aluminium. Preferably the catalyst composition disclosed in the present invention contains: (a) 0.5 to 2 parts by mole of the titanium (IV) or titanium (III) complex; (b) 1 to 4 parts by mole of the cyclopentadienyl complex of silicon (Si), germanium (Ge), or tin (Sn); and (c) 50 to 1,000 parts by mole of the methyl aluminoxane, or a mixture containing 0.5 to 4 parts by mole ofthe non-coordinated Lewis acid and 100 to 1,000 parts by mole of the trialkyl aluminium. Examples of component (b) include tetramethylcyclopentadienyl trimethyl silicon and tetramethylcyclopentadienyl-tri(n-butyl) tin. Examples of titanium complex (a) are triisopropoxy chloro titanium and tetraethoxy titanium. If the activated transitional metal co-catalyst contains the mixture of non-coordinated Lewis acid and trialkyl aluminium, the preferred amount of the cyclopentadienyl complex is from 0.5 to 2 parts by mole. One of the advantages of the catalyst composition disclosed in the present invention is that it causes a very inexpensive chemical, i.e., either TiR' 1 R' 2 R' 3 R' 4 or TiR' 1 R' 2 R' 3 , to exhibit high activity in the production of high-syndiotacticity polystyrene polymers from styrene or other aryl ethylene monomers. TiR' 1 R' 2 R' 3 R' 4 and TiR' 1 R' 2 R' 3 have largely been considered as having only low activity in making syndiotactic polystyrene. With the present invention, the cost of the catalyst can be substantially reduced, compared to the conventional catalysts of similar activity and syndiotacticity. Another advantage ofthe catalyst composition disclosed in the present invention is that it is not very sensitive to degradation by exposure to air and moisture. Most catalysts for the preparation of syndiotactic polystyrene contain cyclopentadiene-coordinated titanium, such as cyclopentadienyl trichlorotitanium and cyclopentadienyl trimethoxytitanium, whose activities are known to be sensitive to air and moisture. The present invention, thus, discloses an improved catalyst composition for the preparation of high-syndiotacticity polystyrene which exhibits superior activities and stability on storage, and can be made at a substantially lowered cost. BRIEF DESCRIPTION OF THE DRAWING The present invention will now be described in greater detail with reference to a preferred embodiment of and with the aid of the accompanying drawing, namely Fig. 1, which is a flow chart diagram showing the steps of a preferred embodiment of the process disclosed in the present invention utilizing an improved catalyst composition for the preparation of high-syndiotacticity polystyrene polymers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention discloses an improved catalyst composition for preparing high-syndiotacticity polystyrene polymers, and the process of utilizing this improved catalyst composition. The improved catalyst composition disclosed in the present invention allows the use of a very economical ingredient thus substantially lowering the manufacturing cost of the catalyst composition, while providing high activity and high syndiotacticity comparable to the best commercial products at substantially higher cost. The activated transitional metal co-catalyst component of the catalyst composition can be methyl aluminoxane (20 to 10,000 parts by mole), or a mixture containing 0.1 to 20 parts by mole of a non-coordinated Lewis acid (a Lewis acid is an electron-pair donor) and 100 to 10,000 parts by mole of a trialkyl aluminium, such as triethyl aluminium or tetraisobutyl aluminium. Preferably the non-coordinated Lewis acid is a borate such as N,N-dimethyl anilinium tetrakis (pentafluorophenyl) borate, triphenyl carbonium tetrakis(pentafluorophenyl)borate, and dialkyl ferrocenium tetrakis(pentafluorophenyl)borate. As discussed above, one of the advantages of the catalyst composition disclosed in the present invention is that it can utilize a very inexpensive chemical (compared to titanocenes), i.e., either TiR' 1 R' 2 R' 3 R' 4 or TiR' 1 R' 2 R' 3 , as an important ingredient to provide high activity catalytic function in the production of high-syndiotacticity polystyrene polymers from styrene or other aryl ethylene monomers. The titanium complexes TiR' 1 R' 2 R' 3 R' 4 and TiR' 1 R' 2 R' 3 have been considered as an ineffective catalyst ingredient in the polymerization of syndiotactic polystyrene because of their relatively poor activity. With the present invention, because it can utilize these inexpensive ingredients while providing comparable or even superior results, the cost of the required catalyst can be reduced by almost one order of magnitude, compared to the conventional catalysts of similar activity and syndiotacticity. Furthermore, most of these conventioned catalysts for the preparation of syndiotactic polystyrene contain cyclopentadiene-coordinated titanium (i.e., titanocenes), such as cyclopentadienyl trichlorotitanium and cyclopentadienyl trimethoxytitanium, which have been known to be highly sensitive to environmental variables such as air and moisture. Another advantage of the catalyst composition disclosed in the present invention is that it is not very sensitive to degradation by exposure to air and/or moisture. The present invention, thus, discloses an improved catalyst composition for the preparation of high-syndiotacticity polystyrene which exhibits superior activities and stability on storage, and can be made at a substantially lowered cost. Fig. 1 is a flow chart diagram showing the steps of a preferred embodiment of the process disclosed in the present invention. A polystyrene reactor maintained at 50 °C is first charged with nitrogen gas to purge air. 110 ml of toluene and an appropriate amount of methyl aluminoxane are added into the reactor, followed by the addition of cyclopentadienyl trimethyl silicon complex and a titanium (IV) complex, TiR' 1 R' 2 R' 3 R' 4 . The reaction mixture is stirred for 5 minutes, then styrene monomers are added to start the polymerization reaction. After about one hour, when the polymerization reaction is complete, the reaction mixture (which contains the reaction product) is quenched with IPA to isolate syndiotactic polystyrene (sps) by precipitation. The syndiotactic polystyrene so obtained is extracted with MEK to remove amorphous polystyrene. The insoluble portion is conventionally called the MIP (MEK-insoluble portion), which is an indication of the ratio between syndiotactic polystyrene and atactic polystyrene. The present invention will now be described more specifically with reference to the following examples. It is to be noted that the following descriptions of examples, including the preferred embodiment of this invention, are presented herein for purposes of illustration and description. Example 1 100 ml of toluene was added into a 450-ml Fisher-Porter bottle, which was equipped with an electrically powered stirrer. The reaction bottle was heated until its internal temperature reached 70 °C, then methyl aluminoxane (containing 6.6 mmole Al) was added. Subsequently, 0.75 ml of 1.6 x 10 -2 M triisopropoxychloro titanium, ClTi(O-iPr) 3 , in toluene, and 0.75 ml of 1.6 x 10 -2 M tetramethylcyclopentadienyltrimethyl silicon in toluene were added. Finally 20 ml of styrene monomer was added to begin the polymerization reaction. After the reaction was continued at 70 °C for one hour, methanol was added to stop the reaction. White syndiotactic polystyrene particles were precipitated from the reaction mixture. After filtration and drying (at 80 °C and under a reduced pressure), 11.35 g of syndiotactic polystyrene were obtained. This represented a catalytic activity of 2.0 x 10 4 g sps/g Ti·hr. The syndiotacticity of the syndiotactic polystyrene so produced was analyzed using NMR to be 98%. A Soxhlet extraction procedure was also performed to measure the apa/sps ratio using methylethyl ketone. The MEK-insoluble portion (MIP) was measured to be 92%. Comparative Example 1 The procedure in Comparable Example 1 was identical to that in Example 1, except that the reaction mixture did not contain tetramethylcyclopentadienyltrimethyl silicon. In this example, the catalyst composition contained only 6.6 mmole of methyl aluminoxane (measured based on the content of Al) and 0.75 ml of 1.6 x 10 -2 M ClTi(O-iPr) 3 in toluene. After the steps of polymerization reaction, precipitation with methanol, filtration, and drying, 0.42 g of sps was obtained, representing a catalytic activity of 8.5 x 10 2 g sps/g Ti•hr. Example 2 100 ml of toluene was added into a 450-ml Fisher-Porter bottle, which was equipped with an electrically powered stirrer. The reaction bottle was heated until its internal temperature reached 70 °C, then methyl aluminoxane (containing 6.6 mmole Al) was added. Subsequently, 0.75 ml of 1.6 x 10 -2 M triisopropoxychloro titanium, ClTi(O-iPr) 3 , in toluene, and 0.75 ml of 1.6 x 10 -2 M tetramethylcyclopentadienyl-tri(n-butyl) tin in toluene were added. Finally 20 ml of styrene monomer was added to begin the polymerization reaction. After the reaction was continued at 70 °C for one hour, methanol was added to stop the reaction. White syndiotactic polystyrene particles were precipitated from the reaction mixture. After filtration and drying (at 80 °C and under a reduced pressure), 3.42 g of syndiotactic polystyrene were obtained. This represented a catalytic activity of 6.0 x 10 3 g sps/g Ti•hr. Example 3 100 ml of toluene was added into a 450-ml Fisher-Porter bottle, which was equipped with an electrically powered stirrer. The reaction bottle was heated until its internal temperature reached 70 °C, then a mixture containing 1.21 ml (4.8 x 10 -3 mole) of triisobutyl aluminium (a trialkyl aluminium) and 0.012 g (1.4 x 10 -5 mole) of N,N-dimethyl anilinium tetrakis (pentafluorophenyl) borate (a non-coordinated Lewis acid) was added. This was followed by the addition of 0.75 ml of 1.6 x 10 -2 M tetraethoxy titanium, Ti(OEt) 4 , in toluene, and 0.75 ml of 1.6 x 10 -2 M tetramethylcyclopentadienyltrimethyl silicon in toluene. Finally 20 ml of styrene monomer was added to begin the polymerization reaction. After the reaction was continued at 70 °C for one hour, methanol was added to stop the reaction. White syndiotactic polystyrene particles were precipitated from the reaction mixture. After filtration and drying (at 80 °C and under a reduced pressure), 7.24 g of syndiotactic polystyrene were obtained. This represented a catalytic activity of 1.3 x 10 4 g sps/g Ti•hr. Example 4 100 ml of styrene was added into a 450-ml Fisher-Porter bottle, which was equipped with an electrically powered stirrer. Then methyl aluminoxane (containing 12 mmole Al) was added. The reaction bottle was heated until its internal temperature reached 70 °C. Subsequently, 2.4 x 10 -5 mole of triisopropoxychloro titanium, ClTi(O-iPr) 3 and 2.4 x 10 -5 mole of tetramethylcyclopentadienyltrimethyl silicon were added to begin the polymerization reaction. After the reaction was continued at 70 °C for 20 minutes, excess amounts of methanol were added to stop the reaction. White syndiotactic polystyrene particles were precipitated from the reaction mixture. After filtration and drying (at 80 °C and under a reduced pressure), 23.34 g of syndiotactic polystyrene (mp = 269 °C) were obtained. This represented a catalytic activity of 6.1 x 10 4 g sps/g Ti•hr. Example 5 50 ml of styrene was added into a 450-ml Fisher-Porter bottle, which was equipped with an electrically powered stirrer. Then methyl aluminoxane (containing 12 mmole Al) was added. The reaction bottle was heated until its internal temperature reached 70 °C. Subsequently, 2.4 x 10 -5 mole of triisopropoxychloro titanium, ClTi(O-iPr) 3 and 2.4 x 10 -5 mole of trimethyl silyl indene were added to begin the polymerization reaction. After the reaction was continued at 70 °C for 20 minutes, excess amounts of methanol were added to stop the reaction. White syndiotactic polystyrene particles were precipitated from the reaction mixture. After filtration and drying (at 80 °C and under a reduced pressure), 23.34 g of syndiotactic polystyrene (mp = 268 °C and syndiotacticity > 95%) were obtained. This represented a catalytic activity of 2.2 x 10 4 g sps/g Ti•hr. The foregoing description of the preferred embodiments of this invention has been presented for purposes of illustration and description. The embodiments were chosen and described to provide the best illustration of the principles of this invention and its practical application to thereby enable those skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.

Claims: A catalyst composition for the preparation of high-syndiotacticity polystyrene or other aryl ethylene polymers from styrene or substituted styrene comprising: (a) 0.1 to 10 parts by mole of a titanium (IV) or titanium (III) complex which does not contain cyclopentadienyl ligand, said titanium complex being represented by the following formula of TiR' 1 R' 2 R' 3 R' 4 or TiR' 1 R' 2 R' 3 , wherein each of said R' 1 , R' 2 , R' 3 and R' 4 is, independently, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an amino group, or a halogen atom; (b) 0.1 to 10 parts by mole of a cyclopentadienyl complex of silicon (Si), germanium (Ge), or tin (Sn) represented by one of the following formulae wherein each of said R 1 , R 2 , R 3 and R 4 is, independently, an alkyl group, an aryl group, a silyl group, a germanyl group, a stannyl group, or a halogen atom; R is an alkyl group, an aryl group, a hydrogen atom or a halogen atom; and X is selected from the group consisting of silicon (Si), germanium (Ge) and tin (Sn); and (c) an activated transitional metal co-catalyst which is either 20 to 10,000 parts by mole of methyl aluminoxane, or a mixture containing 0.1 to 20 parts by mole of a non-coordinated Lewis acid and 100 to 1,000 parts by mole of a trialkyl aluminium; wherein said substituted styrene is a C 1-12 -substituted styrene or a mono- or poly-halogenated styrene. A catalyst composition according to claim 1 characterised in that said trialkyl aluminium contained in said activated transitional metal co-catalyst is selected from trimethyl aluminium, triethyl aluminium, triisobutyl aluminium, tri(n-butyl) aluminium, tri(n-propyl) aluminium, and triisopropyl aluminium. A catalyst composition according to claim 1 or claim 2 characterised in that said non-coordinated Lewis acid contained in said activated transitional metal co-catalyst is borate. A catalyst composition according to claim 1 or claim 2 characterised in that said non-coordinated Lewis acid contained in said activated transitional metal co-catalyst is selected from N,N-dimethyl anilinium tetrakis (pentafluorophenyl) borate, triphenyl carbonium tetrakis(pentafluorophenyl)borate, and dialkyl ferrocenium tetrakis(pentafluorophenyl)borate. A catalyst composition according to claim 1 characterised in that said activated transitional metal co-catalyst comprises a non-coordinated Lewis acid, which is N,N-dimethyl anilinium tetrakis (pentafluorophenyl) borate, and a trialkyl aluminium, which is selected from the group consisting of trimethyl aluminium, triethyl aluminium, triisobutyl aluminium, tri(n-butyl) aluminium, tri(n-propyl) aluminium, and triisopropyl aluminium. A catalyst composition according to any one of claims 1 to 5 characterised in that said cyclopentadienyl complex is tetramethylcyclopentadienyltrimethyl silicon. A catalyst composition according to any one of claims 1 to 5 characterised in that said cyclopentadienyl complex is tetramethylcyclopentadienyl-tri(n-butyl) tin. A catalyst composition according to any one of claims 1 to 7 characterised in that said titanium complex is triisopropoxychloro titanium. A catalyst composition according to any one of claims 1 to 7 characterised in that said titanium complex is tetraethoxy titanium. A catalyst composition according to anyone of claims 1 to 9 characterised in that it contains: (a) 0.5 to 2 parts by mole of said titanium (IV) or titanium (III) complex; (b) 1 to 4 parts by mole of said cyclopentadienyl complex of silicon (Si), germanium (Ge), or tin (Sn); and (c) 50 to 1,000 parts by mole of said methyl aluminoxane, or a mixture containing 0.5 to 4 parts by mole of said non-coordinated Lewis acid and 100 to 1,000 parts by mole of said trialkyl aluminium. A catalytic process for preparing high-syndiotacticity polystyrene or other aryl ethylene polymers from styrene or substituted styrene monomers, wherein said substituted styrene is a C 1-12 -substituted styrene or a mono- or poly-halogenated styrene characterised in that said styrene or substituted styrene monomer is polymerised in the presence as catalyst of a catalyst composition as claimed in any one of claims 1 to 10.

Inventors: PENG SHU-LING, SUE MICKEY, TSAI JING CHERNG, WANG SHIAN-JY, PENG, SHU-LING, SUE, MICKEY, TSAI, JING CHERNG, WANG, SHIAN-JY
Applicants: IND TECH RES INST, INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE
Application year: 1996
Main classification: C08F12
IPC codes: C08F12, C08F4, C08F10