Side chain pendant non‐linear optically active polymers synthesised by grafting reactions on maleic anhydride copolymers

Abstract

AbstractThe synthesis of well defined, high molecular weight polymers for non‐linear optical (NLO) applications has been carried out in an effort to improve the film properties of waveguides fabricated from these materials, Free radical methods of polymerisation result in molecular weight limitations due to the chain transfer nature of the NLO active chromophores, and therefore, in order to prepare a high molecular weight polymer, a post polymerisation grafting method was chosen to incorporate side chain pendant chromophores onto a preformed polymer. Alcoholysis of anhydride copolymers resulted in chromophore incorporation levels of up to 90% of available reactive sites. Additional branching of the linear anhydride prepolymers was also carried out using polytetrahydrofuran but this was not shown to improve the mechanical properties of the fabricated films. Since the anhydride opens to an ester and an acid, in order to reduce the ionic content of the final polymer, further reaction of the generated carboxylic acid group was attempted, resulting in partial diester formation, and an improvement in film quality. Electrical field poling at temperatures close to the glass transition was only successful at low electrical field strengths, allowing electrooptic coefficients of values of up to 2.4 pm/V at a poling field of 80 V/μm to be obtained.