Synthesis and characterization of polymers containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications, 3. Poly(p‐chloromethylstyrene) derivatives

Abstract

AbstractPoly[p‐(4′‐cyanobiphenyl‐4‐yloxymethyl)styrene]s (PCBMS) were prepared by chemical modification of poly(p‐chloromethylstyrene) with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl or free radical polymerization of p‐(4′‐cyanobiphenyl‐4‐yloxymethyl)‐styrene (CBMS). The latter method appeared to be a good one for the preparation of polymers with high glass transition temperature and high chromophore content if performed in dimethyl sulfoxide. There was no real evidence for liquid crystal properties in the resulting polymers, which resemble typical amorphous isotropic polymers. This indicates that these polymers should be considered to be polyethylene containing the benzyl ether of 4‐cyano‐4′‐hydroxybiphenyl as the mesogenic group attached directly to the backbone, and not as polystyrenes containing the cyanobiphenyl group attached to the backbone through a OCH2spacer. Some preliminary Corona poling experiments were performed, and the second harmonic generation coefficients d31 and d33, were measured by Maker fringe analysis. Interestingly, the ratio of d33 to d31 was found to be 6, which is much larger than the value of 3 predicted by the molecular statistical model for electric field poling of isotropic systems. This was attributed to conformational constraints on chromophore ordering as expected in such polymers containing no flexible spacer.