EFFECT OF PREPOLYMER STRUCTURE ON THE ELECTROOPTIC PERFORMANCE OF POLYMER-DISPERSED LIQUID-CRYSTALS

The effect of prepolymer structure on the electro-optic properties of polymer dispersed liquid crystals (PDLCs) prepared from UV-cured polyu rethane acrylates (PUAs) has been studied. Among four types of films w ith different soft-segment structure, polypropylene glycol (PPG)- and polytetramethyl ether glycol (PTMG)-based PUAs gave lower threshold (V -10) and operating (V-90) voltages, whereas polycaprolactone diol (PCL )-based PUAs gave higher V-10 and V-90 voltages. The use of mixed poly ol polypropylene glycol/poly(tetramethylene adipate)diol) (PPG/PTAd) g ave an electro-optic response intermediate between the two. Regarding the effect of hard segment type, that from a linear aliphatic diisocya nate (hexamethylene diisocyanate, HDI) gave the lowest V-10 and V-90 v oltages as well as transparent-translucent transition temperature comp ared with those from cycloaliphatic diisocyanates. This was interprete d in terms of a more flexible nature and hence a lower glass transitio n temperature of HDI-based PUA. (C) 1998 SCI.