Radiochemical studies of free‐radical vinyl polymerizations. Part I. The nature of the initiation and termination processes in methyl methacrylate and styrene polymerizations using C14‐labeled initiators

Abstract

AbstractC14‐Labeled initiators, viz., di‐(ar‐C14)‐benzoyl peroxide, di‐(carboxyl‐C14)‐benzoyl peroxide, and C14‐azobisisobutyronitrile (AZBN), have been used to initiate the polymerization of methyl methaerylate at 60°C. in benzene. Determination of the rates of polymerization, and the molecular weights (M̄n) and C14‐contents of the resultant polymers permits the following conclusions to be made. (1) Rates of initiation by benzoyl peroxide and AZBN are given by the equations, Ri = 5.15 × 10−6 [Bz2O2] mole l.−1 sec.−1 and Ri = 1.17 × 10−5[AZBN] mole l.−1 sec.−1, respectively. (2) The initiator efficiency, f, for AZBN is 0.50; f for benzoyl peroxide cannot be evaluated in the absence of a reliable kd value for this compound in the present system. (3) Initiation is solely by addition of initiator radicals, R·, to the monomer; in the case of benzoyl peroxide, 43% of the radicals R· are phenyl and 57% are benzoyloxy under the reaction conditions used. (4) The average number of C14‐initiator fragments per polymer molecule, n, is 1.27, indicating that bimolecular termination of polymethyl methacrylate radicals is 57.5% by disproportionation and 42.5% by combination.