SYNTHESIS AND CHARACTERIZATION OF POLYMERS CONTAINING 4-CYANOBIPHENYL-BASED SIDE-GROUPS FOR NONLINEAR-OPTICAL APPLICATIONS .3. POLY(P-CHLOROMETHYLSTYRENE) DERIVATIVES

Poly[p-(4'-cyanobiphenyl-4-yloxymethyl)styrene]s (PCBMS) were prepared by chemical modification of poly(p-chloromethylstyrene) with the sodi um salt of 4-cyano-4'-hydroxybiphenyl or free radical polymerization o f p-(4'-cyanobiphenyl-4-yloxymethyl) styrene (CBMS). The latter method appeared to be a good one for the preparation of polymers with high g lass transition temperature and high chromophore content if performed in dimethyl sulfoxide. There was no real evidence for liquid crystal p roperties in the resulting polymers, which resemble typical amorphous isotropic polymers. This indicates that these polymers should be consi dered to be polyethylene containing the benzyl ether of 4-cyano-4'-hyd roxybiphenyl as the mesogenic group attached directly to the backbone, and not as polystyrenes containing the cyanobiphenyl group attached t o the backbone through a --O--CH2-- spacer. Some preliminary Corona po ling experiments were performed, and the second harmonic generation co efficients d(31) and d(33) were measured by Maker fringe analysis. Int erestingly, the ratio of d(33) to d(31) was found to be 6, which is mu ch larger than the value of 3 predicted by the molecular statistical m odel for electric field poling of isotropic systems. This was attribut ed to conformational constraints on chromophore ordering as expected i n such polymers containing no flexible spacer.