Polymerization of dialkyl itaconates with dimethyl azoisobutyrate (5) was studied in benzene at 50 "C by means of electron spin resonance (ESR). The monomers used are dimethyl (l), diethyl (2), dibutyl (3) and di-2-ethylhexyl (4) itaconates. All the polymerization systems involve ESRobservable propagating polymer radicals under the actual polymerization conditions. The polymerization rate (R,) and degree of polymerization of the resulting polymer increase in going from shorter to longer alkyl groups. The ESR-determined rate constants of propagation (k,) and termination (k,) decrease as the alkyl chain becomes longer. k, of 1 is 3,3 times higher than that of 4, while k, of 1 is 590 times higher than that of 4. Thus, the steric effect due to the alkyl group suppresses much more termination than propagation, leading to the fact that R, increases as the alkyl group becomes larger.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.