Functionalization of polysiloxanes by esterification of pendant epoxy groups: Cross‐linkable liquid polymers containing photo‐dimerizable ester units

Photo-dimerizable carboxylic acids were grafted onto linear silicone copolymers by amine catalyzed esterification of pendant epoxypropyl groups. The epoxy-carboxy reaction was found to surpass in experimental simplicity, chemical selectivity and reproducibility, the modification methods involving the hydrosilylation of functionalized olefins. Liquid, photo-crosslinkable polymers (8a and 8b) were finally obtained after acetylation of the hydroxy-ester groups resulting from the addition of functional carboxylic acids, and no unwanted side-reaction was detected. The practical sensitivity of photo-reactive polysiloxanes of various average molecular weights containing 5–17 mol-% of sensitive units, was measured by photoresist type insolubilization tests. The ultimate acetylation reaction was shown to have little or no influence on the dimerization process of 2-cyano-5-phenyl-2,4-pentadienoic derivatives (8a), but to increase the rate of disappearance of trans-cinnamic groups (in 8b) submitted to UV light irradiation.