X-RAY-SCATTERING STUDY OF THE POLYMERIZATION MECHANISM AND PHASE-TRANSITIONS OF THE DIACETYLENE - BIS-(PARA-TOLUENE-SULPHONATE) OF 2,4 HEXADIINE 1,6 DIOL

The authors present an X-ray study of the topochemical polymerization in the crystalline state of the diacetylene: bis-(p-toluene sulphonate) of 2,4 hexadiine 1,6 diol. From the observation of diffuse scattering in sheets perpendicualr to the b* direction and in the layers of Bragg reflections, one can deduce directly that the mechanism of polymerization proceeds homogeneously inside the monomer crystal: long polymer chains along the b direction growing at random throughout the lattice. Furthermore, the large decrease of the b lattice constant with the increase of the polymer content is shown to be homogeneous: both monomer and polymer chains adopting locally the same periodicity along the b direction, with value intermediate between that of the pure monomer and that of the pure polymer crystals. Finally a study between 100 K and 300 K, of the phase diagram of the pure monomer revealed two phase transitions: at 206 K to an incommensurable modulated structure described by the temperature dependent wave vector q//I//I equals 0. 5 a* plus or minus delta (T) b* and at 163 K to a commensurable superstructure described by the wave vector q//I//I//I equals 0. 5 a*. The polymer crystal presents only one phase transition at 206 K to the superstructure described by the wave vector q//I//I//I.