Diffusion-controlled atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) is a promising technology which can produce polymers with well-controlled structure and functionality under mild reaction conditions. Although tremendous progresses have been made in the area over the past decade, there are still several major challenges on its road to commercialization. One of the challenges is the lack of control over polymer molecular weight caused by diffusion limitations of reactants. This thesis focused on the study of diffusion-controlled reactions involved in ATRP either at high monomer conversions or in crosslinking systems. The main objectives are to elucidate the radical mechanism of ATRP and to develop strategies for the preparation of specialty polymers. This sandwich-type thesis is organized based on five refereed journal papers first-authored by the candidate.; Severity of heterogeneity issues involved in a bulk ATRP of methyl methacrylate (MMA) was amplified and demonstrated in an ampoule reactor having small diameter and high aspect ratio (L/D). It was found that the Cu(II) concentration, monomer conversion, and polymer molecular weight varied from location to location along the ampoule reactor. Typical nine-line methacrylate free radical signals were observed at high monomer conversions by an off-line electron spin resonance (ESR) spectroscopy due to the radical trapping caused by diffusion limitations.; An on-line ESR study was carried out in the ATRP of MMA and ethylene glycol dimethacrylate (EGDMA). Different amounts of EGDMA were used to simulate different levels of diffusion limitations. The radical and Cu(II) concentrations were recorded and quantitatively analyzed. Methacrylate radical signals appeared at a range of intermediate conversions due to diffusion limitations imposed by network formation. It was found that the diffusion-controlled radical deactivation was responsible for the radical accumulation. The effects of comonomer composition, catalyst and initiator concentrations, as well as temperature on the radical and Cu(II) concentration profiles were examined, The ESR study was extended to several representative ATRP systems with various catalysts to provide a unified view of the radical mechanism. Methacrylate radical signals were observed in all the systems.; A bulk ATRP of MMA and EGDMA was carried out to prepare branched and crosslinked polymers. (Abstract shortened by UMI.)...