Effect of polymerization conditions on the microstructure of a liquid crystalline copolyester

The melt polycondensation of mixtures of sebacic acid (S), 4,4'-diacetoxybi phenyl (B), and 4-acetoxybenzoic acid (H), carried out for the synthesis of semiflexible liquid-crystalline copolyesters referred to as SBH 1 : 1 :x, has been studied with the aim of clarifying the effect of the reaction cond itions on the microstructure and the thermal properties of the products. It has been shown that the segregation of a liquid-crystalline phase within t he polymerizing mixture, coupled with the thermody namic tendency of the tw o phases to undergo compositional differentiation as polymerization proceed s, is responsible for the formation of blocky, rather than ideally random, copolyesters with poor processibility, when the mole ratio of H to the othe r two monomers is higher than x approximate to 1.90. The results of this st udy have shown that this unwanted effect can be considerably limited by car rying out the polycondensation at a relatively high temperature from the ve ry beginning, rather than by the standard technique involving progressive h eating of the reaction mixture, thus allowing the production of SBH copolye sters with a higher degree of aromaticity. The results are discussed in ter ms of the relative rates of the condensation reactions, which are responsib le for chain growth, and of the concurrent acidolysis and esterolysis react ions leading to copolyester sequence reorganization. (C) 2000 John Wiley & Sons, Inc.