One-pot synthesis of methacrylic acid–ethylene oxide branched block and graft copolymers

Abstract

Despite the large volume of academic literature on the synthesis and physico-chemical characterization of block copolymers and their potential for application in a wide variety of products, relatively few of these materials have been commercialized. More often than not the main obstacle to this is the high cost of synthesis versus the extra value added to potential products. Devising more cost-effective routes to block copolymers therefore remains an important challenge to polymer chemists. Using conventional solution free radical polymerization we have now synthesized, each in one-pot, architecturally complex ‘branched diblock copolymers’ and compositionally related ‘grafted branched copolymers’, exploiting a generic branching synthetic methodology developed in our own laboratory. In each case blocks of poly(methacrylic acid) and poly(ethylene glycol) (PEG) are involved. The first group was obtained by copolymerization of methacrylic acid with a PEG dimethacrylate with branching favoured in competition with crosslinking by use of appropriate levels of free radical chain transfer agent. For the second series methacrylic acid has been copolymerized with a PEG monomethacrylate and ethylene glycol dimethacrylate, again with crosslinking inhibited by use of a chain transfer agent. Good yields of products are obtained and typically the polymerization mole feed compositions have been chosen to yield an even mass balance of poly(methacrylic acid) and PEG blocks in the copolymers, though this parameter is readily adjustable. The molecular composition of the products has been characterized by elemental microanalysis and ¹H NMR spectroscopy, with the latter also combining with multi-angle light scattering size exclusion chromatographic (MALS/SEC) molar mass data to provide information on the branching architecture. The products are complex mixtures in terms of both architecture and molar mass, but the synthetic strategy is far simpler, more practical and more cost-effective than alternative routes to structurally more uniform analogues via multi-step living polymerization procedures are likely to be. The materials are therefore complementary to, rather than competitive with, these analogues. The present approach lends itself to efficient scale-up, and could make significant quantities of materials readily available for further physico-chemical characterization and applications evaluation.