Synthesis and aqueous solution properties of novel neutral/acidic block copolymers

The synthesis of novel acidic diblock copolymers via group transfer polymer isation (GTP) is described. Oligo(ethylene glycol) monomethyl ether monomet hacrylate (OEGMA) was copolymerised with either benzyl methacrylate (BzMA) or tetrahydropyranyl methacrylate (THPMA). The BzMA and THPMA act as protec ted monomers for the methacrylic acid residues, which cannot be polymerised directly using GTP. Provided that the BzMA content of the copolymer is not too high, the benzyl groups can be selectively deprotected by catalytic hy drogenolysis to give the corresponding methacrylic acid copolymers. However , incomplete debenzylation of BzMA-rich copolymers and contamination of the final deprotected copolymers with catalyst residues limited the utility of this synthetic route. On the other hand, THPMA-based copolymers could be d eprotected by acidic hydrolysis under mild conditions to give well-defined OEGMA-MAA copolymers. In this case quantitative deprotection was achieved r egardless of the block composition and no catalyst contamination problems w ere encountered. In addition, aqueous GPC confirmed that the narrow molecul ar weight distributions of the precursor blocks were retained in the final OEGMA-MAA copolymers, Hence, although THPMA is not commercially available, it is preferred to BzMA for the convenient synthesis of OEGMA-MAA block cop olymers. Finally, reversible micellisation of selected OEGMA-MAA block copo lymers was observed in aqueous media. In the presence of 1 M K2CO3 the OEGM A chains form the micelle cores, whereas the neutral MAA block forms the mi celle core at pH 1. In both cases NMR studies suggest that the micelle core s remain highly hydrated. (C) 2000 Elsevier Science Ltd. All rights reserve d.