NMR studies of free-radical polymerization and copolymerization of monomers and polymers containing allyl groups

Abstract

Reactivity ratios for free-radical copolymerization of allyl acetate (A) with (i) methyl methacrylate (M), (ii) n-butyl acrylate (B) and (iii) styrene (S) have been evaluated from either copolymer compositions or dyad fractions determined by 1H and 13C-NMR spectroscopy; the values obtained are respectively: (i) r A = 0.024 ± 0.009 and r M = 41 ± 6, (ii) r A = 0.04 ± 0.02 and r B = 11.7 ± 1.0, and (iii) r A = 0.021 ± 0.001 and r s = 66 ± 4. These values indicate that in copolymerizations of allyl methacrylate with (meth)acrylates and styrene, conversion of the allylic CC bonds will only become significant when the extent of reaction of all other types of CC bonds has reached very high values. NMR studies of the structure of poly(allyl methacrylate) formed by both bulk and dilute solution polymerization have provided no evidence for the in-chain lactone rings which may result from intramolecular cyclopolymerization of allyl methacrylate; the signals in the NMR spectra of poly(allyl methacrylate) are entirely consistent with “normal” polymerization at the methacrylic and allylic CC bonds. Theoretical predictions based upon the measured reactivity ratios, and results from a model reaction, indicate that the very low concentrations of pendant methacrylic CC bonds which result from polymerization of the allylic CC bonds in molecules of allyl methacrylate, make a significant contribution to grafting and crosslinking.