Nucleobase-mediated stereospecific radical polymerization and combination with RAFT polymerization for simultaneous control of molecular weight and tacticity.

A highly soluble thymine-based compound (1-octyl thymine), having an array of hydrogen bonding sites with an ADA sequence (A and D: proton acceptor and donor sites, respectively), was used to mediate the stereospecific radical polymerization of an acrylamide monomer [N-(6-acetamidopyridin-2-yl)acrylamide] possessing the complementary DAD sequence. The thymine derivative interacted with the monomer via the selective 1:1 and strong triple hydrogen-bonding interaction (K = 1.1 × 10(3) in CHCl(3) at 20 °C) and mediated the syndiospecific radical polymerization of the monomer to give syndiotactic rich polymers up to r = 84% in CH(2)Cl(2) at -78 °C. A combination with the RAFT polymerization enabled simultaneous control of the molecular weight (M(W)/M(n) ≈ 1.5) and tacticity (r = 73% and 76% at 60 and 20 °C, respectively) of the resulting polymers. Furthermore, the stereoblock polymerization was achieved upon the addition of the thymine-based mediator during the RAFT polymerization to give the atactic-syndiotactic stereoblock polymers with controlled molecular weights.