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

Photoinduced living radical polymerization has been employed to synthesize alpha,omega-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 ((D) over bar = 1.18) with high conversion (>98%) achieved throughout all the iterative monomer additions. Crucially, a reduced temperature (15 degrees C) was found to result in an observed decrease in the dispersities (1.14 vs 1.45) as opposed to when higher temperatures (50 degrees C) were employed. A number of bifunctional initiators were employed, including ethylene bis(2-bromoisobutyrate) (EbBiB), a PEG initiator (average M-w = 1000 g mol(-1)), and bis[2-(2'-bromoisobutyryloxy)ethyl] disulfide ((BiBOE)2S2), resulting in narrow dispersed multiblock copolymers in various molecular weights (DPn similar to 2/13/50/100 per block). Impressively, a high molecular weight undecablock (11 blocks) copolymer of M-n = 150 000 g mol(-1) and (D) over bar = 1.22 was also synthesized. In order to demonstrate the symmetry of the resulting telechelic materials, a well-defined tridecablock (13 blocks, (D) over bar = 1.18, M-n = 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 ((D) over bar = 1.10, M-n = 12 400 g mol(-1)).