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RAFT Polymerization of Vinylthiophene Derivatives and Synthesis of Block Copolymers Having Cross-Linkable Segments

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journal contribution
posted on 13.10.2009, 00:00 by Hideharu Mori, Ken Takano, Takeshi Endo
The polymerization of three vinylthiophene derivatives, 2-vinylthiophene (2VT), 3-vinylthiophene (3VT), and 2,5-dibromo-3-vinylthiophene (DB3VT), was carried out by reversible addition−fragmentation chain transfer (RAFT) process using six different chain transfer agents (CTAs). The novel doubly polymerizable monomer, DB3VT, undergoes controlled radical polymerization via the RAFT process, followed by Suzuki coupling reaction. Two dithiobenzoate-type RAFT agents, phenylethyl dithiobenzoate (CTA 2) and cumyl dithiobenzoate (CTA 3), were the most efficient to obtain poly(DB3VT) with controlled molecular weights and low polydispersities (Mw/Mn = 1.05−1.15). Good control of the polymerization of DB3VT was confirmed by the linear increase in the molecular weight with the conversion and the ability to extend the chain by a second addition of the monomer. Chain extension from poly(methyl methacrylate) to DB3VT could be well controlled under suitable conditions and provided block copolymers having cross-linkable poly(DB3VT) segments with as-designed chain structures and low polydispersities. The block copolymers were also synthesized by RAFT polymerization of DB3VT using poly(methyl acrylate) as a macro-chain transfer agent (macro-CTA). Modifications of the 2,5-dibromide group of poly(DB3VT) by Suzuki coupling reaction using difunctional boronic acid afforded a network material, whereas a soluble composite having an extended π-structure was obtained by the coupling reaction of the block copolymer, poly(methyl methacrylate)-b-poly(DB3VT).