STRUCTURAL BEHAVIOR AND PHOTOCHEMICAL REACTIVITY OF SILICONE COPOLYMERS WITH FUNCTIONAL SIDE-GROUPS

In order to rationalize the peculiar photochemical behavior of some si licone copolymers containing cyanostyrylacrylic (CSA) side groups conn ected to the main chain through a branched spacer, thermophysical stud ies including microscopic, calorimetric and diffractometric analysis w ere conducted. An oligomeric trisiloxane containig the same type of fu nctionality was also studied as a model compound. Although CSA acid an d its simple alkyl ester derivatives exhibit only true crystalline ord er, layered (smectic or crystalline) structure was evidenced for the m odel compound. The series of reactive polysiloxanes containing various amounts of functional units shows phase separatioin. The photosensiti ve esters are gathered with part of the main chains in the ordered mic rodomains dispersed in a silicone-rich phase. The weight fraction of r eactive side groups in the mixed microdomains was determined by calori metric measurements indicating an almost unchanged composition of the microphases from one polymer to another. Several observations based on bulk state photochemistry showed a leveled reactivity independent of the macroscopic content in photosensitive groups. The layered order ob served by wide angle X-ray scattering is consistent with the clean, re versible photoreaction and with the observed kinetics.