Solid-state reaction kinetics in single-phase polymerizations

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Abstract
The kinetics of single‐phase solid‐state polymerization reactions are evaluated using two different approximations for the effect of structural changes at intermediate conversions. Conversion curves are calculated for monomer phases which undergo large dimensional changes in the reaction direction (crystal strain approximation) and for monomer phases which are essentially dimensionally invariant during reaction (nearest neighbor approximation). Using the crystal strain approximation and experimentally derived elastic constants, the different autocatalytic reaction curves observed for thermal and radiation‐induced polymerization of a diacetylenic monomer are successfully predicted. The dramatic autocatalytic effect for thermal polymerization can be explained quantitatively by a strain‐dependent rate of chain initiation and chain propagation, while the weaker autocatalytic effect for γ‐ray induced polymerization suggests that radiation‐induced chain initiation is relatively insensitive to crystal strain. Chain propagation lengths as a function of conversion and the effects of external stress and impurities on reaction kinetics are also predicted using the model.

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