Living Cationic Isomerization Polymerization of Pinene

Living Cationic Isomerization Polymerization of Pinene -...

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Living Cationic Isomerization Polymerization of ± -Pinene. 2. Synthesis of Block and Random Copolymers with Styrene or p -Methylstyrene Jiang Lu, 1 Masami Kamigaito, and Mitsuo Sawamoto* Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-01, Japan Toshinobu Higashimura Department of Materials Science, School of Engineering, The University of Shiga Prefecture, Hikone, Shiga 522, Japan Yun-Xiang Deng Department of Chemistry, Zhongshang University, Guangzhou 510275, China Received July 23, 1996; Revised Manuscript Received October 29, 1996 X ABSTRACT: Block copolymers of ± -pinene with styrene (St) or p -methylstyrene ( p MeSt) were prepared by the sequential living cationic polymerizations initiated with the HCl adducts of styrene ( 1b : HCl - St) or 2-chloroethyl vinyl ether ( 1a : HCl - CEVE), respectively, in the presence of isopropoxytitanium trichloride [TiCl 3 (O i Pr)] and tetra- n -butylammonium chloride ( n Bu 4 NCl) in CH 2 Cl 2 at - 40 °C. As for the ± -pinene - St pair, both AB and BA block copolymers ( M h w / M h n 1.3) were obtained by this method. With p MeSt, the addition of ± -pinene to the living p MeSt polymers gave block copolymers with narrow molecular weight distributions (MWDs) ( M h w / M h n 1.2), whereas the reverse order of addition led to block copolymers with broad MWDs ( M h w / M h n 1.9). In the polymerization of a mixture of ± -pinene and St, the former was consumed faster to give tapered copolymers. In contrast, ± -pinene and p MeSt were copolymerized nearly at the same rate to give random or statistical copolymers. Introduction A bicyclic aliphatic monomer abundantly found in natural turpentine, ± -pinene, readily undergoes cationic polymerization to give polymers that contain six- membered rings as repeat units. 2 - 5 The unique back- bone structure originates from the isomerization of the initially bicyclic growing end into the open-chain ter- tiary cation structurally similar to the tert -butyl cation. Despite such a mechanistic complexity, we have recently developed living cationic polymerization of ± -pinene with the use of combinations of the hydrogen chloride adduct ( 1a ) of 2-chloroethyl vinyl ether (CEVE) as initiator and isopropoxytitanium chloride [TiCl 3 (O i Pr)] as activator in the presence of tetra- n -butylammonium chloride ( n Bu 4 NCl) (Scheme 1). 6 This work was to extend this finding to the controlled synthesis of ± -pinene-based block and random copoly- mers with styrene (St) or p -methylstyrene ( p MeSt). Although the homopolymer has already been com- mercialized as resins, few are known for ± -pinene copolymers. According to a recent report, 3 the monomer undergoes azeotropic copolymerization with isobutene, but its block copolymers have not been obtained yet. Recently, we have also found that St can be polym-
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Living Cationic Isomerization Polymerization of Pinene -...

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