EVALUATION OF THE KINETIC-PARAMETERS FOR STYRENE POLYMERIZATION AND THEIR CHAIN-LENGTH DEPENDENCE BY KINETIC SIMULATION AND PULSED-LASER PHOTOLYSIS

Pulsed las er photolysis (PLP) has been employed to determine propagat ion rate constants k(p) for styrene polymerization in benzene over a w ider temperature range (20 - 80-degrees-C) than previously covered. It is proposed that a small chain length dependence of k(p) (overall) ma y, in part, be a consequence of a marked chain length dependence of k( p) for the first few propagation steps [i. e. k(p)(1) > k(p)(2) > k(p) (3) greater-than-or-equal-to k(p) (greater-than-or-equal-to 4)]. The p ropagation rate constant for styrene polymerization is given by the ex pressions: In k(p) = 16,0(9) - 289(50)/(RT) (overall) or ln k(p) = 16, 4(7) - 300(84)/(RT) (chain length greater-than-or-equal-to 4). Kinetic simulation has been applied both as an aid in data analysis and to de monstrate the reliability of the PLP technique for evaluation of propa gation rate constants (k(p)) in radical polymerization. This has been achieved by examining the sensitivity of the molecular weight distribu tion of polymers formed in PLP experiments to the values of the kineti c parameters associated with polymerization and their chain length dep endence. The termination rate constants (k(t) = k(c) + k(d)) and the r atio of combination to disproportionation (k(c):k(d)) markedly affect the molecular weight distribution of polymer formed in PLP experiments . The prospects for evaluating the values of k(t), its chain length de pendence and k(c): k(d) by direct analysis of the molecular weight dis tribution are discussed in the light of these results.