Synthesis and properties of polyurethanes and poly(p-phenylenevinylene) derivatives with high optical nonlinearity

Abstract

A new type of second-order nonlinear optical(NLO) polyurethane containing hemicyanine-type dye was prepared. It shows high second-order nonlinear optical activity, good temporal and thermal stability. A stable, good reproducible value of the macroscopic second-order susceptibility $X^(2)$ in order of $3×10^{-7}$ esu(126 pm/V) was obtained. Three types of second-order NLO cross-linked polyurethanes derived from poly(phenylisocyanate-co -formaldehyde) and hemicyanine derivatives having bulky tetraphenylborate anion were prepared under in-situ conditions which simultaneously poled and thermally crosslinked. The three materials exhibit a second-order activity described by $X^(2)$ value of $4.0~8.9×10^{-8}$ esu(17~37 pm/V). The poled and thermally cured polymeric films exhibit improved temporal stability according to increasing the number of crosslinking site and parallel locking. PPV derivatives containing 4-alkoxy-4``-nitrostilbene as pendant group were prepared. The organic soluble precursor route gave the improved optical film quality and its poling efficiency is higher than that of the water-soluble precursor route. However, the obtained polymer from the organic-soluble precursor route shows glass transition temperature($T_g$) which varied with elimination method and the composition of copolymerization. The polymers showed small second-order nonlinear optical activities(X^(2)$ value = 0.94~4.0 pm/V) because of low β value of chromophore Two NLO polyetherimides derived from Mitsunobu reaction were prepared. Especially, PEI-TCN showed much improved temporal stability despite of non-crosslinked system and relatively medium glass transition temperature. The enhanced temporal stability may be attributed to the interaction between the nonbonding electron of thiophene for electron rich chromophore and tricyanovinyl group, which is a new mechanism for the stabilization of poled state. The two materials exhibited second-order activities described by $X^(2)$ value of 73 ...