Sulfobetaine-containing diblock and triblock copolymers via reversible addition-fragmentation chain transfer polymerization in aqueous media

摘要

A novel bifunctional acrylamido-based reversible addition-fragmentation chain transfer (RAFT) chain-transfer agent (CTA), N,N'-ethylenebis[2-(thiobenzoylthio)propionamide] (CTA2), has been synthesized and used for the controlled free-radical polymerization of N,N-dimethylacrylamide (I)MA). A comparative study of CTA2 and the monofunctional CTA N,N-dimethyl-s-thiobenzoylthiopropionamide (CTA1) has been conducted. Polymerizations mediated by CTA1 result in poly(N,N-dimethylacrylamide) (PDMA) homopolymers with unimodal molecular weight distributions, whereas CTA2 yields unimodal, bimodal, and trimodaxl distributions according to the extent of conversion. The multimodal nature of the PDMAs has been attributed to termination events and/or chains initiated by primary radicals. The RAFT polymerization of DMA with CTA2 also results in a prolonged induction period that may be attributed to the higher local concentration of dithioester functionalities early in the polymerization. A series of omega- and alpha,omega-dithioester-capped PDMAs have been prepared in organic media and subsequently employed as macro-CTAs for the synthesis of diblock and triblock copolymers in aqueous media with the zwitterionic monomer 3-[2-(N-methylacrylamido)-ethyldimethylammonio] propane sulfonate (MAEDAPS). Additionally, an omega-dithioester-capped MAEDAPS homopolymer has been used as a macro-CTA for the block polymerization of DMA. To our knowledge, this is the first example of a near-monodisperse, sulfobetaine-containing block copolymer prepared entirely in aqueous media. The diblock and triblock copolymers form aggregates in pure water that can be dissociated by the addition of salt, as determined by H-1 NMR spectroscopy and dynamic light scattering. In pure water, highly uniform, micellelike aggregates with hydrodynamic diameters of 71-93 nm are formed. (C) 2003 Wiley Periodicals, Inc. [References: 69]