Nonlinear optical polyurethane functionalized with a heteroaromatic thiophene ring having a tricyanovinyl group

A new functionalized polyurethane structure with a thiophene ring having a tricyanovinyl group in the polymer side chain was synthesized. The molecular weight of the final polymer was determined to be M_n = 12000 and M_w/M_n = 2.04. The resulting polymer was soluble in N-methylpyrrolidinone and could be processed into good optical quality films by spin casting at ca. 100 °C. It showed no weight loss up to 266 °C in the thermogravimetric analysis and a definite glass transition at 176 °C. The second-order nonlinear optical coefficient, d₃₃, was determined to be 51 pm V^-1 from measuring the second harmonic generation (SHG) for a thin polymer film after poling treatment. The outstanding orientational stability of the aligned chromophores was observed up to about 150 °C, which originated from the rigid polymer backbone and the stabilizing function of the hydrogen bridges formed between the neighboring polyurethane chains.