Synthesis of Syndiotactic Polystyrene Derivatives Containing Amino Groups Guangxue Xu and T. C. Chung* Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 Received February 18, 2000; Revised Manuscript Received May 31, 2000 ABSTRACT: This paper discusses a new family of syndiotactic polystyrene (s-PS) derivatives containing the amino group, including poly(4-aminostyrene), poly(4-aminomethylstyrene), and poly(4-aminoethyl- styrene). These semicrystalline polymers exhibit high melting temperatures (∼350 °C) and relatively fast crystallization rates. These functional syndiotactic polymers are prepared in two steps. Syndiospecific polymerization of a styrene derivative containing a masking N,N-bis(trimethylsilyl)amino group is achieved by using a half-sandwich titanocene/perfluoroborane catalyst system. This study focused on the catalyst system (catalyst and cocatalyst) that can polymerize functional monomers with high catalyst activity and syndiotacticity. Acid hydrolysis leads to the complete recovery of primary amino groups in s-PS derivatives. Introduction One of the most interesting features of metallocene catalysis is the preparation of syndiotactic polystyrene (s-PS) by half-sandwich titanocene catalysts, 1 such as CpTiCl 3 /MAO and [Cp*Ti(CH 3 ) 3 /B(C 6 F 5 ) 3 ]. The s-PS polymers with high crystallinity exhibit many unique properties, superior to traditional atactic polystyrene (a- PS) prepared by anionic or free radical initiators and isotactic polystyrene (i-PS) prepared by heterogeneous Ziegler-Natta catalyst. The combination of high melting temperature (∼270 °C) with relatively high crystalliza- tion rate, low dielectric constant, high chemical resis- tance, and low specific gravity makes s-PS an attractive material for many applications in the electronic, pack- aging, and automotive industries. Despite some unique properties, s-PS polymer re- sembles a-PS polymer with poor impact strength and low surface energy. The absence of polar groups in hydrophobic polystyrene restricts their end uses, espe- cially where adhesion to substrates (metals, ceramics, glass, etc.) and compatibility 2 with polar polymers are desired. So far, there are only few reports discussing functionalized s-PS copolymers, including sulfonated s-PS, 3 hydroxylated s-PS 4 prepared via poly(styrene-co- 4-tert-butyldimethylsilyloxystyrene) precursor, and s- PS-b-PMMA prepared via borane-terminated s-PS. 5 It has been a long-standing scientific challenge and industrially interesting subject to prepare poly(R-olefin)s containing functional (polar) groups, 6 such as alcohol, amine, ether, ester, etc., by Ziegler-Natta (Z-N) po- lymerization. The facile acid-base interaction between catalytic sites (Lewis acid) and functional groups (Lewis base) usually prohibits the polymerization reaction. Two general approaches of preventing catalyst poisoning include the protection of functional groups by bulky substituents 7 (masking groups) and precomplexization of the functional group with Lewis acids, such as the alkylaluminum cocatalyst. 8 Many attempts in conven- tional Ziegler-Natta systems, containing group III or IV transition metal halides and alkylaluminum cocata- lysts, showed only very limited success. Most of these efforts were in the copolymerization reactions of R-ole- fins with a small amount of protected functional comono- mers. Recently, interest in the functionalization approach has been renewed by using metallocene catalysts. Zir- conocene/methylaluminoxane (MAO) catalysts were used in copolymerization 9 of ethylene and propylene with a small amount of comonomers that have large spacers between the olefin and the functional group, including 1-hydroxy-10-undecene, 9 1-chloro-10-undecene, 10 N,N- bis(trimethylsilyl)-1-amino-10-undecene, 11 and o-hep- tenylphenol. 12 It is believed that MAO (in large excess) may serve as an in-situ protection agent to prevent catalyst deactivation. In fact, the pretreatment of functional monomer with MAO before initiation signifi- cantly increases the catalyst activity. Similar pretreat- ment using trimethylaluminum (TMA) 13 also showed good copolymerization results between R-olefins and hydroxy- and amino-containing monomers using zir- conocene/MAO catalysts. It is interesting to note that the benefit of TMA-protected functional monomers in the copolymerizations 15 is also extended to the less oxophilic late transition metal catalysts. Waymouth et al. 14 reported the advantage of perfluo- roborane cocatalysts (replacing MAO in the metallocene catalyst) that were compatible with the protected func- tional groups. They successfully demonstrated the ho- mopolymerization of several masked monomers, i.e., 5-(N,N-diisopropylamino)-1-pentene and 4-trimethylsi- loxy-1,6-heptadiene, in good yields using zirconocene/ perfluoroborane catalysts. However, stereospecific po- lymerization of functional olefin monomers with metallo- cene catalysts, especially titanocene systems, is an open research area. Detailed experimental results are needed to understand the effects of protected functional group on catalyst activity, stereoselectivity, and polymer mo- lecular weight. Results and Discussion In this paper, we will discuss stereospecific homopo- lymerization of functional styrene derivatives, contain- ing amino groups, using half-sandwich titanocene cata- * To whom all correspondence should be addressed. 5803 Macromolecules 2000, 33, 5803-5809 10.1021/ma000303d CCC: $19.00 © 2000 American Chemical Society Published on Web 07/15/2000