Photoinduced Synthesis of α,ω-Telechelic Sequence-Controlled Multiblock Copolymers

Abstract

Photoinduced living radical polymerization has been employed to synthesize α,ω-telechelic multiblock copolymers of a range of acrylic monomers including methyl acrylate (MA), ethyl acrylate (EA), ethylene glycol methyl ether acrylate (EGA), and solketal acrylate (SA). Under carefully optimized conditions, a well-defined tricosablock (23 blocks) copolymer was obtained (Đ = 1.18) with high conversion (>98%) achieved throughout all the iterative monomer additions. Crucially, a reduced temperature (15 °C) was found to result in an observed decrease in the dispersities (1.14 vs 1.45) as opposed to when higher temperatures (50 °C) were employed. A number of bifunctional initiators were employed, including ethylene bis(2-bromoisobutyrate) (EbBiB), a PEG initiator (average Mw = 1000 g mol–1), and bis[2-(2′-bromoisobutyryloxy)ethyl] disulfide ((BiBOE)2S2), resulting in narrow dispersed multiblock copolymers in various molecular weights (DPn ∼ 2/13/50/100 per block). Impressively, a high molecular weight undecablock (11 blocks) copolymer of Mn = 150 000 g mol–1 and Đ = 1.22 was also synthesized. In order to demonstrate the symmetry of the resulting telechelic materials, a well-defined tridecablock (13 blocks, Đ = 1.18, Mn = 25 000 g mol–1) was synthesized utilizing a bifunctional disulfide initiator which was cleaved postpolymerization, yielding a narrow disperse polymer at half the molecular weight of the parent polymer (Đ = 1.10, Mn = 12 400 g mol–1).