Graft copolymers from natural rubber latex using visible, ultraviolet, and γ‐ray initiation

Abstract

AbstractGraft copolymers have been prepared from natural rubber latex and methyl methacrylate using visible, ultraviolet, and γ‐radiation. The influence of monomer concentration, temperature, radiation intensity, and, in the case of photoinitiation, photosensitizer concentration, on polymerization rates and molecular weights have been studied. The proportion of graft polymer is very high initially but falls with conversion and with increase in monomer concentration. Photoinitiated grafting depends on the photosensitizer and on temperature, but with γ‐initiation the fraction grafted is independent of temperature. In the latter case the high proportion of graft cannot be explained in terms ofthe relative G values and concentrations of monomer and rubber. The fall‐off in proportion of graft with conversion is thought to result from microscopic heterogeneous regions formed during polymerization, which are believed to increase in size as polymerization proceeds, thereby reducing further the possibility of grafting. Degradation of previously grafted polymer by prolonged irradiation is not of consequence in this case. Molecular weights of grafted and ungrafted polymers are very similar, except at low monomer concentrations, and a marked feature of this system is their constancy with change in all reaction conditions other than monomer concentration. Estimates of the utilization of radiation energy have been made and it is concluded that on an energy basis γ and photoinitiated reactions are of comparable efficiency.