X-ray topographic studies of solid-state reactions. II. Solid-state polymerization of 2,4-hexadiynediol bis( p -toluene sulphonate)

Abstract

A synchrotron X-ray topographic examination has been made of the structural changes that occur during the polymerization of 2,4-hexadiynediol bis( p -toluene sulphonate) monomer crystals by radiolytic, photolytic and thermal means, in situ in the synchrotron X-ray beam. Exposure of the monomer crystals to the full synchrotron X-ray beam ( λ ≈ 0.01-0.3 nm) yields rapid polymerization which results in the complete transformation of monomer crystal to polymer crystal by a single crystal to single crystal transformation. Filtering the softer components ( λ > 0.1 nm) from the beam allowed the extension of the induction period to polymerization to an extent which enabled the study of structural changes that occurred during preliminary photo and thermal polymerization before the initiation of rapid X-ray polymerization. The results show that radiolytic and photolytic polymerization initiate and progress uniformly in the bulk and surface regions of the crystal respectively. These processes are not apparently influenced by the presence of dislocations or other recognizable structural defects (twins and growth sector boundaries) in the crystal. In contrast, thermal polymerization initiates in the locus of bundles of growth dislocations and inclusions in the crystal. Single dislocations do not appear to act as nuclei. The mechanism by which preferential nucleation can occur at groups of dislocations is discussed.