ORGANIC NLO POLYMERS .2. A STUDY OF MAIN-CHAIN AND GUEST-HOST-CHI((2)) NLO POLYMERS - NLO-PHORE STRUCTURE VERSUS POLING

Several new dipolar main-chain chi(2) nonlinear optical (NLO) polymers were prepared. The NLO-phores, based on alkoxy substituted alpha-cyanoacrylates, were also placed as monomeric guests within a poly(methyl methacrylate) host. Polar alignment of the NLO-phores by corona poling and their relaxation behavior was monitored by detecting the optical signal resulting from the second harmonic generation. The study revealed that two dipolar rigid-rod main-chain NLO polymers (NLOPs), having solubilizing side chains, were not responsive to alignment by corona poling. We found that each main-chain NLOP prepared in the study showed a strong resistance to alignment, whereas virtually the same NLO-phore as a guest within a polymer host responded well to corona poling. When small variations were made in the structure of the NLO-phore, it was found that when hydrogen-bonding groups are rigidly coupled to the NLO-phore they were very effective for retaining polar asymmetry induced by poling and induced no deleterious effects on the alignment process. For main-chain NLOPs, it appears for optimum alignment the bonding axis and the polar axis should not be parallel.