Computer simulation of polymerizing CR-39

Abstract

Abstract A computer program which models the free radical addition polymerization of a tetrafunctional monomer on a 3-D lattice is presented. The actual polymerization of CR-39 is complex, with the importance of the competing reactions changing with the extent of reaction, the initial peroxide initiator concentration and the temperature. The model presented here is a static model with one tetrafunctional monomer being placed on each site of a three-dimensional array. Radicals are introduced at random and the growing chains are allowed to propagate at random throughout the lattice until terminated by radical recombination or chain transfer. The model incorporates the features of allylic polymerization. Hydrogen abstraction is allowed for and the ratio between degradative chain transfer and effective chain transfer can be varied. Although the model does not incorporate diffusion it can be used qualitatively to investigate some of the properties of the system. The gel point, at which the largest macromolecule assumes infinite size, can be predicted. The structure of the polymer around the gel point could well influence the final homogeneity of the plastic. The distribution of cluster sizes is given by the program. The program also incorporates bulk etching, in the sense that the distribution of etch products can be predicted. Such distributions can be compared with experimental distributions and along with comparisons of ultimate monomer conversion can give clues as to the predominate chain termination reactions in CR-39. The track response of CR-39 will be strongly influenced by the structures in the polymer, and this model will prove useful in understanding the performance of CR-39 in track detection.