Functionalized Syndiotactic Polystyrene Polymers Prepared by the Combination of Metallocene Catalyst and Borane Comonomer J. Y. Dong, E. Manias, and T. C. Chung* Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 Received December 20, 2001; Revised Manuscript Received March 4, 2002 ABSTRACT: This paper discusses an effective route in the functionalization of s-PS polymer that involves the direct copolymerization of styrene with a borane-containing styrenic monomer, i.e., 4-[B-(n-butylene)- 9-BBN]styrene (B-styrene). The reactivity ratios of the two comonomers are quite close, with r1 ) 0.9 for styrene and r2 ) 1.2 for B-styrene in the Cp*Ti(OMe)3/MAO catalyst system. A broad composition range of syndiotactic poly(styrene-co-B-styrene) copolymers has been prepared with narrow molecular weight and composition distributions. The random copolymer structure was further evidenced by DSC and 13 C NMR analyses. With increasing B-styrene concentration, the copolymers show a systematic decrease in glass transition temperature, melting point, crystallization temperature, and crystallinity. At above 8.4 mol % B-styrene content, the crystallinity of the copolymer completely disappears. In turn, the borane groups in the copolymer are very versatile and can be quantitatively converted to other functional groups, such as hydroxy and anhydride groups, or transformed to free radical initiators for in situ free radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. Introduction One of the most important advances in metallocene technology is the preparation of syndiotactic polystyrene (s-PS) 1 that exhibits high melting point (∼270 °C) and a relatively high crystallization rate that is several orders of magnitude 2 faster than that in isotactic polystyrene (i-PS). s-PS is a novel engineering plastic made from an inexpensive commodity monomer. Despite its unique properties, s-PS polymer also has several drawbacks that pose serious concerns in many commercial applications. Because of a high melting point, the required melt processing temperature at >300 °C (near the polymer decomposition temperature) causes a major problem in polymer processability. A modified s-PS polymer with a slightly reduced melting point (to about 250 °C) would be a very desirable material. In addition, s-PS polymer has poor impact strength and low surface energy, similar to traditional atactic poly- styrene prepared by free radical and anionic processes. So far, there are only a few reports discussing the modification of s-PS polymer, including sulfonation 3 and bromination 4 of s-PS and hydroxylated s-PS 5 prepared via poly(styrene-co-4-tert-butyldimethylsilyloxystyrene) precursor. Recently, Xu and Chung also reported a new method using dialkylborane containing a B-H group as a chain transfer agent during metallocene-mediated styrene polymerization to form borane-terminated syn- diotactic polystyrene, 6 which was further engaged in the free radical chain extension with methyl methacrylate (MMA) to form s-PS-b-PMMA diblock copolymers. Several years ago, we developed a very useful method to functionalize polyolefins, such as polyethylene (PE) and polypropylene (PP), which involved direct copoly- merization 7 of R-olefin and borane-containing R-olefin by Ziegler-Natta and metallocene catalysts. Because of the excellent stability of borane moieties to catalysts and the good solubility of trialkylborane in hydrocarbon media, a broad range of borane-containing polyolefin copolymers with uniform molecular structure were prepared without sacrificing catalyst activity. In addi- tion, the incorporated borane groups in the polyolefin copolymers are very versatile and can be effectively interconverted to various functional groups under mild reaction conditions and also transferred to polymeric radicals for graft reactions 8 to prepare polyolefin graft copolymers, such as PP-g-PMMA and PE-g-PMMA. We extended this borane monomer approach to s-PS to prepare functionalized s-PS polymers and s-PS graft copolymers that not only contain desirable functional groups but also have lower melting temperatures with improved processability. Results and Discussion Borane-Containing Monomer. As illustrated in Scheme 1, a new borane-containing monomer of 4-[B- (n-butylene)-9-BBN]styrene was prepared by a two-step reaction. After completing a coupling reaction between allylmagnesium chloride and vinyl benzyl chloride to form 4-(3-butenyl)styrene, containing a styrenic olefin and an R-olefin groups, this resulting asymmetrical diene was selectively monohydroborated by 9-BBN at the R-olefinic double bond in an anti-Markovnikov manner. Both reaction steps are very effective and produce high yields. Figure 1 compares the 1 H NMR spectra of 4-[B-(n-butylene)-9-BBN]styrene (B-styrene) and 4-(3- butenyl)styrene. After hydroboration reaction by a sto- ichiometric amount of 9-BBN, all the chemical shifts at * To whom all correspondence should be addressed. Scheme 1 3439 Macromolecules 2002, 35, 3439-3447 10.1021/ma012215e CCC: $22.00 © 2002 American Chemical Society Published on Web 03/27/2002