Synthesis of Hydroxy-Telechelic Poly(methyl acrylate) and Polystyrene by Atom Transfer Radical Coupling

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Abstract

Hydroxy-terminated poly(methyl acrylate) (HO-PMABr) and polystyrene (HO-PStBr) were synthesized by atom transfer radical polymerization (ATRP) using a HO-functionalized initiator. These HO-functional polymers were further employed in an atom transfer radical coupling (ATRC) reaction in the presence of a zerovalent metal forming hydroxy-telechelic poly(methyl acrylate) (HO-PMA-OH) and polystyrene (HO-PSt-OH). In ATRC process macroradicals, generated in situ by an atom transfer radical equilibrium, take part in bimolecular termination reactions in the presence of a reducing agent, such as nanosize copper. The coupling of hydroxy-terminated PSt was fast; after 3 h more than 95% of polymeric chains being reacted. Under similar ATRC conditions, the coupling of poly(methyl acrylate) was slow since the ATRP equilibrium constant, and consequently radical concentration, is much smaller than those of polystyrene. This difficulty was overcome by introducing small amounts of St in the ATRC of polyacrylate. The acrylate radicalsgenerated during the activation step in the presence of cuprous halide complexreact with styrene producing styrene-terminated acrylate macroradicals that combine in a similar manner and at rates similar to polystyrene chains. Equimolar amounts of St vs polyacrylate chain end provided hydroxy-telechelic polymers with high coupling efficiency after a short reaction time. NMR analyses performed on the coupling product of hydroxy-terminated poly(methyl acrylate) showed the incorporation of catalytic amounts of St during ATRC.

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