Product and Kinetic Analysis of Oligomerization by Addition-Fragmentation Chain Transfer using Methyl alpha-Bromomethylacrylate

摘要

Radical additions of 2-cyano-2-propyl radicals to styrene (St), methyl methacrylate (MMA), and ethyl acrylate (EA) in the presence of large amounts of addition fragmentation chain transfer (AFCT) agent, methyl alpha-bromomethylacrylate (MBMA), gave low molecular weight unsaturated oligomers. The methylene protons of the omega-unsaturated end groups can be distinguished by ~1H NMR spectroscopy depending on the number and the structure of the monomer units bound to the end groups. The reltive amounts of oligomers containing one, two or three monomer units and the unsaturated end group were determined to evaluate the rate constants for chain transfer relative to propagation of the oligiomer radicals. The rate constants for chain transfer were greater than those for propgtion and the ratio of these rate constants depended on the chain length of the oligomer radical. MBMA gave its dimer together with the oligomers of St, MMA, and EA. These results confirm that propagating radicals smoothly add to MBMA to yield the adduct radical exclusively undergoing beta-framgentation and that homopropagation of MBMA is much slower than those of the monomers to function as an effective AFCT agent.