A numerical procedure is developed which allows taking into account the chain length dependence of the termination and propagation constants for calculating molecular weight distributions (MWDs) formed under free-radical polymerization initiated by an arbitrary sequence of laser pulses. The law
where k 0 p is a constant close to the experimentally determined propagation rate constant, k 1 p is the constant of the propagation of radicals with unity degree of polymerization, b 1 and b 2 are constants reflecting the chain length dependences of the propagation of long-chain and ultra-short radicals, respectively) is considered for description of the chain length dependence of the propagation constant. The effect of this dependence on MWDs is considered in detail. It is shown that the time dependence of the chain length of growing radicals, w(t), can be used for model-independent determination of chain-length-dependent propagation constants k L p . Theoretically the well-known pulsed laser polymerization (PLP) method for evaluation of the propagation constant can be used for determination of w(t), but this determination is questionable in practice. Direct application of this method gives L L
The consideration of methyl methacrylate polymerization at 25 8C as an example shows that the weak chain length dependence of the longchain k p value with b 1 a 0.01 can not be revealed by the PLP method. The effect of the chain length dependence of the propagation constant on model-independent determination of termination constants by timeresolved single-pulse pulsed laser polymerization (TR-SP-PLP) technique is investigated. It is shown that for the methyl methacrylate polymerization at 25 8C this technique gives k LYL t values of long-chain radicals with uncertainty F10% for b 1 A 0.01 (if the propagation constant is assumed to be equal to a constant value) and k LYL t ak L p values of these radicals with uncertainty a 6% for b 1 a 0.05. It is shown that the accuracy of determination of both k LYL t and k LYL t ak L p values of short-chain radicals by TR-SP-PLP technique is very low, and that the increase of used laser intensity leads to a considerable improvement of this accuracy.