Synthesis of poly(2-hydroxyethyl methacrylate) end-capped with asymmetric functional groups via atom transfer radical polymerization

Abstract

Poly(2-hydroxyethyl methacrylate) (PHEMA) end-capped with living chloride and alkyne groups was synthesized via ATRP of HEMA using CuCl/CuCl₂/2,2′-bipyridine as a catalyst in a solvent mixture of methanol and 2-butanone. The effects of parameters including the initiator, solvent, temperature and initial monomer to initiator ratios on polymerization were studied in terms of polymerization kinetics, the degree of polymerization (DP) and molar mass dispersity (Đ) of the resulting PHEMA polymer. ATRP of HEMA using propargyl 2-bromoisobutyrate (PBiB) as an initiator was poorly controlled, but those using 3-(trimethylsilyl)propargyl 2-bromoisobutyrate (TMSPBiB) and 3-(triisopropysilyl)propargyl 2-bromoisobutyrate (TiPSPBiB) as initiators were well-controlled. Moreover, the apparent propagation rate constant for ATRP of HEMA using the TMSPBiB initiator was higher than that using the TiPSPBiB initiator. The solvent mixture of methanol–2-butanone at different compositions greatly affected the polymerization controllability. A high molecular weight PHEMA sample with a DP of 1000 and a Đ of 1.34 was obtained under appropriate conditions. The poly(2-hydroxyethyl methacrylate)-block-poly(butyl acrylate) (PHEMA-b-PBA) diblock copolymer was prepared through ATRP of BA using (CH₃)₃Si–CC–PHEMA–Cl as a macroinitiator. The methoxyl polyethylene glycol-block-poly(2-hydroxyethyl methacrylate) (MPEG-b-PHEMA) diblock copolymer was prepared by click reaction between MPEG-N₃ and HCC–PHEMA–Cl. These two reactions demonstrated the reactivity of the asymmetric functional groups end-capping the PHEMA, and further provided modular examples for the synthesis of a novel well-defined (co)polymer with complex architectures.