Thermotropic polyesters: Synthesis and properties of poly(p-oxybenzoate-co-m-phenylene terephthalate)s

DSC, TMA, hot‐stage microscopy and WAXS have been used to examine the effect of concentration of angular units and molecular weight on the thermal transitions of poly(p‐oxybenzoate‐co‐m‐phenylene terephthalate)s. Copolymers containing molar fractions of m‐phenylenedioxy units between 0·20 and 0·30 are melt processable nematogenic materials. In contrast, poly(p‐oxybenzoate‐co‐p‐phenylene isophthalate)s remain nematogenic over a wider concentration range (0·20–0·40) of angular isophthaloyl units. Comparison of fibres produced from copolymers with the same fraction of angular units (0·25) indicates that those with isophthaloyl units have a higher modulus than those with m‐phenylenedioxy units. These differences are ascribed to differences in planarity of chains containing isophthaloyl and m‐phenylenedioxy units, respectively.