Electro-optic properties of CO2 fixed-polymer/nematic LC composite films

Bis(cyclic carbonate) was obtained from the epoxide and CO, reaction with a quaternary ammonium halide salt catalyst. Cyclic carbonate derivatives were then reacted with amine to obtain quantitatively poly(hydroxy)urethanes that were reacted with isophorone diisocyanate (IPDI) and end capped with acrylate to form prepolymers. These prepolymers were mixed with reactive diluents and nematic LCs, and subjected to UV cure to form polymer/LC composite films in a transparent cell. Three types of diglycidyl ether [poly(propyleneglycol), cyclohexane, bisphenol A], three types of endcapping acrylates [2-hydroxyethyl acrylate (HEA), a-hydroxypropyl acrylate (HPA), and 2-hydroxyethyl methacrylate (HEMA)], three types of multyfunctional diluents [tripropylene glycol diacrylate (TPGDA), trimethylolpropane triacrylate (TMPTA), dipentaerythritol hydroxy penta/hexa acrylate (DPHPA)], and three types of photoinitia tors (Irgacure-651, Irgacure-184, Darocure-1173) were incorporated to control the morphology, and hence, the electro-optic properties of the polymer/nematic LC composite films. Poly(propylene glycol) diglycidyl ether segment of polyurethane acrylate (PUA) showed lower viscosity and gave larger domain size resulting in lower threshold (V,,) and driving (V,,) voltages, together with larger nematic-isotropic transition temperature depression. HEA end-capped PUA gave larger polymer-LC phase separation and smaller V-10 as well as V-90. TPGDA-based PUA showed the lowest V-10 and V-90 and the shortest response time. Among the three types of photoinitiators used Irgacure-651 showed the larger LC domain, and smaller V-10 and V-90. (C) 2001 John Wiley & Sons, Inc.