Whiskers: 13. Polyesters based on 4,4′-biphenyldiol and biphenyl-4,4′-dicar☐ylic acid

Abstract

Acetylated 4,4′-biphenydiol (ABD) and biphenyl-4,4′-dicar☐ylic acid (BDCA) were polycondensed in inert aromatic reaction media at various temperatures and monomer concentrations. At temperatures ≤300°C oligoesters were obtained, which according to infra-red and 13C nuclear magnetic resonance cross-polarization/magic-angle spinning spectroscopic characterization preferentially possess two car☐yl end-groups. Furthermore, polycondensations were conducted at 400°C whereby high-molecular-weight polyesters were obtained. Electron microscopy revealed the formation of lengthy crystallites, but true needle-like whiskers were never formed. Analogous polycondensations were conducted with acetylated hydroquinone and BDCA or with ABD in combination with terephthalic acid. Furthermore, all three polyesters were prepared by polycondensation of the free diphenols with terephthaloyl chloride or biphenyl-4,4′-dicar☐ylic acid dichloride in Marlotherm-S at 400°C. Highly crystalline polyesters were obtained whenever the polycondensations were conducted at 400°C in Marlotherm-S, but in all cases the morphology was that of irregular particles. Wide-angle X-ray diffraction powder patterns measured with synchrotron radiation up to 440°C revealed that all three polyesters undergo a gradual transition from an orthorhombic crystal lattice to pseudo-hexagonal and finally to hexagonal chain packing with increasing temperature. These transitions cover a temperature range of more than 400°C. Only in the case of the polyester derived from hydroquinone and BDCA was a reversible first-order phase transition observed around 506°C.