Reactions on Vinyl Isocyanate/Maleimide Copolymers: NLO-functionalized Polymers with High Glass Transitions for Nonlinear Optical Applications

Abstract

A new reactive copolymer system with high, but still variable glass-transition temperatures was synthesized. This was accomplished by copolymerizing various N-substituted maleimides with methylvinyl or vinyl isocyanate, so that a polymer with a 1:1 composition of the two monomers is obtained. Further functionalization is then possible with any nucleophile known from comparable low molecular weight reactions. With different substituents attached to the imide-ring, Tg can be adjusted between 120 and 210 °C. Two effects of the substituent at the imide nitrogen are observed. Bulky groups reduce the mobility of the chain and lead to high Tg values. A similar tendency is found for smaller, less flexible substituents. In this case, the inter- and intramolecular forces of hydrogen-bonding (urethanes) contribute to the effects for high Tg's. The potential of these copolymers was highlighted here for NLO chromophores. A variety of different NLO chromophores was attached to the polymer backbone by reaction of a hydroxyalkyl-containing chromophore with the isocyanate groups, thereby forming urethane linkages between chromophore and polymer. The polymers functionalized in this way show nearly unchanged glass transition temperatures and offer thus the possibility to prepare NLO polymers with high Tg values and good solubility. It is important that even base labile NLO chromophores and systems labile to radical conditions can be fixed easily. The advantage of this system is highlighted by the fixation of NLO chromophores with tricyanovinyl (C2), tricyanochinodimethane (C3) and heterocyclic acceptors (C4). With one of these systems a d33 value of 53 pm/V could be obtained for a loading with only 12 wt % of chromophore.