NEW POLYMER SYNTHESES - 96 - STAR-SHAPED LC-POLYESTERS DERIVED FROM BETA-(4-HYDROXYPHENYL) PROPIONIC-ACID AND 4-HYDROXYBENZOIC ACID

Star-shaped polyesters were prepared by polycondensation of tetraaceto xyspirobis(indane) and a 1 : 1 mixture of silylated beta-(4-acetoxyphe nyl)propionic acid and silylated 4-acetoxybenzoic acid. The lengths of the star arms were systematically varied, and the influence of the st ar center on the stability of the nematic phase was studied. It was fo und that on the average more than 10 monomer units per star arm are re quired to stabilize a homogeneous LC-phase. Furthermore, a second clas s of star-shaped polyesters consisting of beta-(4-hydroxyphenyl)propio nic acid (HPPA), 4-hydroxybenzoic acid (HBA), and 6-hydroxy-2-naphthoi c acid (HNA) was prepared. This ternary copolyester proved to reduce t he crystallinity but to stabilize the LC-character. A homogeneous nema tic melt was obtained with 6 monomer units per star arm. This interpre tation is based on optical microscopy which provides a static picture of the biphasic situation. Therefore, a preliminary study of the melt rheology was included, which proved that the typical LC-character of t he melt was detectable at even shorter star arms due to the shear orie ntation. (C) 1998 John Wiley & Sons, Inc.