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

The synthesis of novel acidic diblock copolymers via group transfer polymerisation (GTP) is described. Oligo(ethylene glycol) monomethyl ether monomethacrylate (OEGMA) was copolymerised with either benzyl methacrylate (BzMA) or tetrahydropyranyl methacrylate (THPMA). The BzMA and THPMA act as protected 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 hydrogenolysis 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 deprotected by acidic hydrolysis under mild conditions to give well-defined OEGMA-MAA copolymers. In this case quantitative deprotection was achieved regardless of the block composition and no catalyst contamination problems were encountered. In addition, aqueous GPC confirmed that the narrow molecular 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 copolymers. Finally, reversible micellisation of selected OEGMA-MAA block copolymers was observed in aqueous media. In the presence of 1 M K2CO3 the OEGMA chains form the micelle cores, whereas the neutral MAA block forms the micelle core at pH 1. In both cases NMR studies suggest that the micelle cores remain highly hydrated. (C) 2000 Elsevier Science Ltd. All rights reserved.