Synthesis and characterization of acrylamido-based polymers via reversible addition-fragmentation chain transfer polymerization
The controlled radical polymerization of N,N -disubstituted acrylamido-based monomers was investigated using a technique known as Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization. Four studies were conducted to assess the effectiveness of RAFT for the synthesis of well-defined (co)polymer architectures. The first study investigated the influence of chain transfer agent (CTA) architecture on the controlled polymerization of N,N -dimethylacrylamide (DMA) in benzene. The efficiency of four CTAs were evaluated including two previously reported CTAs and two novel amide-based CTAs N,N -dimethyl-s-thiobenzoylthiopropionamide (CTA 111 ) and N,N -dimethyl-s-thiobenzoylthioacetamide (CTA 112 ). Analysis of the polymerization kinetics and molecular weight (MW)/polydispersity (PDI) control revealed that the acrylamido-based CTAs were highly effective since their leaving groups reflect the electronic and structural characteristics of the propagating chain. The second study addressed the influence of CTA architecture on the polymerization kinetics and MW/PDI control for the aqueous RAFT polymerization of DMA. Two CTAs were evaluated including CTA 111 and sodium 4-cyanopentanoic acid dithiobenzoate (CTA 110 ). In pure water, the use of CTA 111 resulted in poor molecular weight control and a prolonged inhibition period. Higher polymerization temperatures and the addition of a miscible organic cosolvent were beneficial for control. The third study examined the synthesis of near-monodisperse polysulfobetaines directly in aqueous salt media. The monomeric betaines 3-[2-(N -methylacrylamido)-ethyldimethylammonio]propanesulfonate (MAEDAPS), 3-[N -(2-methacroyloyethyl)-N,N-dimethylammonio]propanesulfonate (DMAPS), and 3-(N,N -dimethylvinylbenzyl-ammonio)-propane sulfonate (DMVBAPS) were polymerized using CTA 110 . The methacrylic- and styrenic-sulfobetaines exhibited higher degrees of MW control than the analogous acrylamido-sulfobetaine. The observed differences were rationalized in terms of the differing reactivity and steric bulk of the respective macro-radicals. The fourth study examined the synthesis of stimuli-responsive AB and BAB block copolymers of DMA (neutral 'A' block) and MAEDAPS (sulfobetaine 'B' block). Poly(N,N -dimethylacrylamide) (PDMA) and polysulfobetaine (PMAEDAPS) macro-CTAs were synthesized either organic or aqueous media. A novel bifunctional amide-based CTA, N,N ' -ethylenebis(2-(thiobenzoylthio)-propionamide), was used to prepare a bifunctional PDMA macro-CTA. The macro-CTAs were then employed for the synthesis of di- and triblock copolymers. The associative nature of the sulfobetaine segments in water resulted in the formation of well-defined polymeric 'micelles' of varying hydrodynamic size as determined by dynamic light scattering measurements.