Modification reactions on thermotropic liquid-crystalline poly(ethylene terephthalate-co-oxybenzoate)s with bi- and trivalent 2-oxazoline couplers

Carboxy-terminated liquid-crystalline poly(ethylene terephthalate-co-oxybenzoate)s with 60 and 75 mol-% oxybenzoate units were modified with phenyl-1,4-bis(2-oxazoline) and phenyl-1,3,5-tris(2-oxazoline) in plasticorder and extruder. The modification gave rise to significant increase in molecular weights and also slight crosslinking and branching. The course of the reaction was followed by means of torque-vs.-time curves measured during the plasticorder modification. In spite of strong increase in melt viscosities the processability of the modified copolyesters was not worsened. Samples were injection-moulded and tested. Modifications improved the mechanical properties, distinctly. Especially, samples which were slightly crosslinked with phenyl-1,3,5-tris(2-oxazoline) demonstrated outstanding tensile and impact strengths. Significant differences in fracture behaviour could be evidenced by recording impact bending tests.