Chain‐length‐dependent termination rate constant: Effect on molecular weight distributions formed by pulsed laser radical polymerization

For polymerization initiated by an arbitrary sequence of laser pulses a numerical technique for calculating molecular weight distributions (MWDs) is developed, which takes into consideration the chain length dependence of the termination rate constant k t . The MWDs for methyl methacrylate and styrene are calculated by use of α and k 0 values (for the law k = k 0 ( i ) −α of termination of radicals with chain length i ) and averages {article}{empty}{document}(i, j){document} (for rate constants k = k 0 {article}{empty}{document}(i, j){document} of termination of radicals with different degrees of polymerization) taken from the literature. The dependences of the overall termination constant 〈 k t 〉 on initiation parameters (pulse repetition rate ( v ) and pulse intensity for initiation by periodic laser pulses) are presented. Two methods are proposed for α and k 0 determination: (a) by experiments on polymerization with periodic laser pulses where monomer‐to‐polymer conversions per pulse are determined for different v ; (b) by experiments on polymerization with packets of pulses where the constant k p (the rate constant of propagation), α and k 0 can be determined simultaneously from MWD. For both methods simple analytical equations are derived for evaluation of the constants. The limits of application of the methods are determined by use of the numerical technique for MWD calculation.