PHOTOCROSSLINKABLE 2ND-ORDER NONLINEAR-OPTICAL POLYMERS SYNTHESIZED BY CATIONIC COPOLYMERIZATION

Photocrosslinkable second-order nonlinear optical (NLO) polymers were synthesized from cationic copolymerization of a vinyl ether monomer bearing 4'-nitrobiphenyl-4-oxy group as the NLO chromophore with a vinyl ether monomer bearing cinnamoyl group as the photoreactive moiety. To obtain a suitable poling method involving photocrosslinking, which is capable of inducing a higher and more stable second-order nonlinear coefficient, d(33) for NLO polymer films, some poling procedures were investigated. An optimized poling method was as follows. Ultraviolet (W) irradiation is performed for 90 sec during poling at 50 degrees C for 20 min, followed by poling al 150 degrees C for 20 min. By using this poling method NLO polymer films exhibited a higher and considerably stable d(33) value at room temperature, even though they had rather lower glass transition temperatures before photocrosslinking. Some photocrosslinking mechanism for NLO polymers investigated here were considered.