Influence of Monomer Structure on the Propagation Kinetics of Acrylate and Methacrylate Homopolymerizations Studied via PLP‐SEC in Fluid CO₂

Summary: Propagation kinetics of free‐radical homopolymerizations of methyl acrylate, dodecyl acrylate, butyl methacrylate, dodecyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate in solutions containing 40 wt.‐% CO 2 were studied applying the PLP‐SEC technique. The obtained apparent propagation rate coefficients, k p,app , are by up to 40% below the associated bulk k p values. This reduction is assigned to a lowering of local monomer concentration, c M,loc , at the site of the free‐radical chain end rather than to a decrease of the actual propagation rate coefficient. With the alkyl (meth)acrylates, intersegmental interactions between polar groups of the same polymer molecule are responsible for deviations of c M,loc from the analytical overall monomer concentration, c M,a . Increasing size of the flexible alkyl ester group reduces the differences between c M,loc and c M,a due to shielding effects. Methacrylates with cyclic ester groups do not follow this trend. In case of isobornyl methacrylate, which polymerizes to a rigid material with large side groups, relative size of monomer and CO 2 matters and reduces c M,loc significantly below c M,a .