Polymerization of a polydiacetylene single crystal under hydrostatic pressure

It is reported that the autocatalytic effect found upon thermal polymerization of PTS under atmospheric pressure vanishes at p ≊ 3 kbar and that the reaction becomes of first order. The rate constant K rises almost exponentially with pressure. Up to 6 kbar the activation energy is independent of p. The disappearance of the autocatalytic effect is explained in terms of pressureinduced equalization of monomer and polymer lattice dimensions along the chain direction whereas the increase in K must be due to a decrease of the head to tail distance between neighbouring CCCC monomer units. In terms of thermodynamics the entropy of activation for the polymerization reaction must increase under pressure.