Study of the cross‐linking mechanism of a copolymer containing an electrooptic chromophore

Abstract

AbstractThe mechanism of the cross‐linking reaction occuring between an NLO chromophore copolymerized with a glycidyl epoxide unit (polymer PIII) was rationalized using magic angle spinning (MAS) NMR spectroscopy. A first study conducted on a system composed of a model chromophore and a simple epoxy molecule enabled us to attribute the NMR changes that accompany the epoxy ring opening. Further, the use of a guest–host system made of an azo chromophore dispersed in an MMA–GMA copolymer matrix indicated a quantitative yield of the carboxyl/epoxy anchorage reaction after 30 min of heating at 140°C. The 13C cross polarization (CP)/MAS NMR spectroscopic study showed unambiguously that the cross‐linking reaction in polymer PIII is due to a nucleophilic opening of the epoxy rings by the carboxylic groups of the chromophores resulting in carboxylic ester bond formation. Finally, the blue shift of the ca 500 nm absorption band was modeled with a computational study. It is concluded that the esterification of the acid carboxylic group of the chromophore causes the torsion of the azo molecule. Copyright © 2005 John Wiley & Sons, Ltd.