Synthesis of cationic macromonomers by living polymerizations for comb-branched polyelectrolytes.

摘要

Cationic macromonomers of poly [2-(dimethylamino) ethyl methacrylate dimethylsulfate] (polyDMAEMA-DMS) were synthesized by both living nitro-anionic polymerization with a novel capping technique and atom-transfer radical polymerization (ATRP). The macromonomers were copolymerized with acrylamide to give well-defined comb-branched polyelectrolytes having polyacrylamide (PAM) backbone and polyDMAEMA-DMS side chains by free radical processes.; First, the radical mechanism involved in ATRP was investigated using an electron spin resonance (ESR) spectrometer and a differential scanning calorimeter (DSC). Poly (ethylene glycol) dimethacrylate (PEGDMA) was used as a model system for this purpose of mechanism elucidation. The network-forming feature of the system imposed diffusion limitations to radical deactivation reactions and thus allowed us to directly observe the radical intermediates during the polymerization by the first time.; The polyDMAEMA macromonomers bearing terminal allyl moieties were synthesized by the ATRP method using allyl-containing organic halide as initiator. The polyDMAEMA macromonomers with styrenic end groups were prepared by the living nitro-anionic polymerization. A novel capping technique was developed to improve the initiator efficiency in the anionic polymerization. The polyDMAEMA macromonomers were quaternized with dimethyl sulfate yielding cationic polyDMAEMA-DMS macromonomers.; The copolymerization of acrylamide with polyDMAEMA-DMS macromonomers was conducted using 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AIBA) as free radical initiator in aqueous solution. The reactivity ratios in copolymerization were measured for the two series of cationic macromonomers with terminal styrenic or allyl groups. PolyDMAEMA-DMS macromonomer with styrenic end group was found to have a much higher reactivity than acrylamide. It was attributed to the hydrophobic characteristic of styrenic group and the micelle formation of the macromonomer in aqueous media. In contrast, the PolyDMAEMA-DMS macromonomer with terminal allyl group had lower reactivity than acrylamide. This difference in reactivities caused a chemical composition drifting during the copolymerization. A semi-batch method was used to control the copolymer composition for synthesizing comb-branched cationic polyelectrolytes.