In order to rationalize the peculiar photochemical behavior of some silicone copolymers containing cyanostyrylacrylic (CSA) side groups connected to the main chain through a branched spacer, thermophysical studies including microscopic, calorimetric and diffractometric analysis were conducted. An oligomeric trisiloxane containig the same type of functionality was also studied as a model compound. Although CSA acid and its simple alkyl ester derivatives exhibit only true crystalline order, layered (smectic or crystalline) structure was evidenced for the model compound. The series of reactive polysiloxanes containing various amounts of functional units shows phase separatioin. The photosensitive esters are gathered with part of the main chains in the ordered microdomains dispersed in a silicone-rich phase. The weight fraction of reactive side groups in the mixed microdomains was determined by calorimetric 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 observed by wide angle X-ray scattering is consistent with the clean, reversible photoreaction and with the observed kinetics.