Further improvement of the macroscopic NLO coefficient and optical transparency of hyperbranched polymers by enhancing the degree of branching

Abstract

In this paper, two new second-order nonlinear optical (NLO) hyperbranched polytriazoles (HP1 and HP2) containing nitro azobenzene as the chromophore were successfully prepared, through the AB₄-type click polymerization under copper(I) catalysis. Thanks to the AB₄-type branched monomer, the degree of branching (DB) of HP1 was improved to 0.691, much larger than that of its analogue, HPS1 (0.457), which was derived from an AB₂-type monomer. The solubility, optical transparency and NLO coefficient of HP1 were all improved in comparison with those of HPS1, due to the better site-isolation effect. Furthermore, pentafluorophenyl rings were utilized as isolation groups to further enhance the NLO effect in HP2, and the d₃₃ value and the d_33(∞) value of HP2 were tested to be as high as 136 pm V⁻¹ and 28 pm V⁻¹, respectively.