A numerical method is developed to compute the development of molecular weight distribution （MWD） curves of linear polymers undergoing chain scission. The method can be applied to complex chain scission kinetics and for arbitrarily complex initial MWD curves. Our method is based on the method of lines （MoL）. Different from the existing numerical scheme, we propose the use of logarithmically spaced points. This development ensures the accuracy of the computed MWD curves at low molecular weights, and it does not require a very fine discretization to produce an accurate result.
The intrinsic relationship between molecular chain length and the probability of chain reaction during poly（lactic acid） （PLA） hydrolysis was investigated by Monte Carlo simulation. The chain reaction rate was calculated by introducing a power function of different molecular chain lengths. The hydrolysis of both amorphous and extended-chain crystal PLA was selected as the model system. It is found that, the chain reaction probability was proportional to the chain length with a power of 0.4 for amorphous PLA and 0.7-1 for extended-chain crystal PLA, respectively. These results indicate that PLA with longer chain length usually exhibits larger reaction rate than that with shorter length. Comparing the hydrolysis of the two kinds of PLA, the competition between longer and shorter chains in the different condensed structures is different.
