A Raman study of the disorder induced by polymer chains in mixed monomer-polymer crystals of the diacetylene pTS-D

摘要

The evolution of the high frequency modes of polymer chains in mixed monomer-polymer crystals of fully deuterated diacetylene 2,4-hexadiynylene bis(p-toluenesulfonate) has been studied as a function of the temperature by Raman scattering using IR sources. This compound undergoes topochemical complete polymerization in the crystalline state: that gives the possibility to control the polymer content x from 0 to 100%. In both pure monomer and polymer crystals, an antiferroelectric phase transition occurs at T_c = 182 K in the polymer and, through an intermediary incommensurate phase, from 155 to 195 K in the pure monomer. The evolution of an elongation mode of the conjugated diacetylene backbone is reported in mixed monomer-polymer crystals as a function of the temperature and polymer content from x=20% to x=90%. This mode is coupled to the order parameter. Our results are compared with the previous data obtained for the pure polymer. The influence of disorder induced by polymer chains in mixed monomer-polymer crystals is discussed in a qualitative way.