Solvent effect on radical polymerization of butyl acrylate

The propagation and termination rate constants k p and k t for the radical polymerization of butyl acrylate initiated by biacetyl have been measured by using the rotating‐sector method, in various solvents at 30°C. The value of k p and initiation rate R i varied with solvents, while the value of k t did not change with solvents except for benzonitrile. The variation of k p with aromatic solvents has a trend against Hammett σ p of the solvent substituents similar to that for methyl methacrylate or phenyl methacrylate except for the value in benzonitrile, when it is larger than the variation for methyl methacrylate or phenyl methacrylate. The larger variation of k p for butyl acrylate is compatible with the view that the origin of the solvent effect lies in complex formation between the propagating radical and aromatic solvent molecules. The exceptional decrease in k p and k t in benzonitrile is explained by a contraction of the poly(butyl acrylate) chain in the poor solvent.