Thermal Polymerization of Polydiacetylene. A Comparison between Theory and Experiment Employing Pressure and Contraction Studies

Thermal polymerization of PTS has been measured under hydrostatic pressure up to 6 k bar as a function of temperature. It is found that the induction time for autocatalytic reaction acceleration decreases much faster with pressure than predicted by Baughman's theory. The rate constant used to describe the first order reaction regime increases with pressure according to exp( p / p 0 ) with p 0 = 1.68 ± 0.05 kbar. Both effects are shown to arise from the components of hydrostatic force field acting perpendicular to the polymer chain direction and facilitating bond formation between neighboring monomer molecules. — Measurement of the lattice contraction along b ‐direction as a function of conversion at 1 bar indicates agreement with Baughman's theory which is based on the change of the elastic strain energy in b ‐direction. It is concluded that this theory describes thermal polymerization of PTS at constant pressure but cannot account for reaction acceleration by lateral compression of the lattice. An explanation for the independence of the activation energy on conversion and pressure is suggested.