Synthesis and nonlinear optical properties of a novel polyurethane containing cyanovinylthiophene with enhanced thermal stability of dipole alignment for electro-optic applications

摘要

Stabilization of electrically induced dipole alignment is one of the important criteria in the development of nonlinear optical (NLO) polymers for electro-optic device applications. Polyurethanes for NLO applications have attracted attention because of their high thermal stability due to hydrogen bonding. In the work reported here, we designed and synthesized a new type of NLO polyurethane, in which the pendant NLO chromophores are part of the polymer backbone. This mid-type NLO polymer is expected to have the merits of both main-chain and side-chain NLO polymers, namely stable dipole alignment and good solubility. 1-[3,4-Di-(2-hydroxyethoxy)phenyl]-2-(2-thienyl)ethene was prepared and condensed with 3,3'-dimethoxy-4,4'-biphenylenediisocyanate to yield a polyurethane. This polyurethane was reacted with tetracyanoethylene to give a novel Y-type polyurethane (7) containing 1-(3,4-dioxyphenyl)-2-[5-(1,2,2-tricyanovinyl)-2-thienyl]ethenes as NLO chromophores, which constitute part of the polymer backbone. Polyurethane 7 is soluble in common organic solvents such as N,N-dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of ca 162℃. The second harmonic generation (SHG) coefficient (d_(33)) of a poled polymer film of he polyurethane at 1560 nm fundamental wavelength is ca 1.11 x 10~(-18) C. Polymer 7 exhibits an enhanced thermal stability and no significant SHG decay is observed below 150°C, which is acceptable for NLO device applications.