Improving the initiation efficiency in the single electron transfer living radical polymerization of methyl acrylate with electronic chain-end mimics
2011
Nguyen, Nga H. | Rosen, Brad M. | Percec, Virgil
Computational studies on the heterolytic bond dissociation energies and electron affinities of methyl 2-bromopropionate (MBP) and ethyl 2-bromoisobutyrate (EBiB) in the dissociative electron transfer (DET) step of single electron transfer living radical polymerization (SET-LRP) of methyl acrylate (MA) combined with kinetic experiments were performed in an effort to design the most efficient initiation system. This study suggests that EBiB is more effective than MBP in the SET-LRP of acrylates catalyzed by Cu(0) wire, thus being a true electronic mimic of the dormant PMA species. EBiB allows for a more predictable dependence of the molecular weight evolution and distribution. This is exemplified by the absence of a deviation in the PMA molecular weight from theoretical values at low conversions, as a result of a faster SET activation with EBiB than with MBP. The enhanced control over molecular weight evolution was also observed in the SET-LRP of MA initiated with bifunctional initiators similar in structure to MBP and EBiB, suggesting a higher reactivity than MBP in the SET activation, which matches closely that of the polymer dormant chains. The use of bifunctional initiators in conjunction with activated Cu(0) wire in SET-LRP allows for dramatically accelerated polymerizations, although still providing for exceptional control of the molecular weight evolution and distribution.
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