| Abstract: | The polycondensation of 3-(4-hydroxy phenyl)-propionic acid, 4-Hypp, by means of acetanhydride or acetylchloride was conducted either in the presence or in the absence of a liquid reaction medium. DSC measurements, polarizing microscope, and X-ray diffraction studies indicate poly(4-Hypp) possesses at about 215°C a reversible first order transition between two solid phases. Copolyesters containing various mole ratios of 4-Hypp and 4-hydroxy benzoic acid, 4-Hybe, were prepared by bulk condensation with acetanhydride at 320°C. At 4-Hypp/4-Hybe ratios less than 1.0:1.5 the reaction product was heterogeneous, containing crystals of pure poly(4-Hybe). Neither increasing the reaction time nor the variation of the transesterification catalyst resulted in an entirely homogeneous copolyester. However, for 4-Hypp/4-Hybe ratios greater than 1.0:1.5, 13C NMR spectra indicate perfectly random sequences. Also, terpolyesters containing 3-chloro-4-hydroxy- or 3,5-dichloro-4-hydroxy-benzoic acid were heterogeneous with less than 30 mol % 4-Hypp. DSC measurements revealed for all polyesters a glass transition in the range of 55–78°C. Temperature dependent X-ray diffraction studies confirm that the solid phase is a s.c. LC-glss. Correspondingly low heat distortion temperatures were found by thermomechanical analyses. The copolyesters display under the polarizing microscope LC-phase up to temperatures of 450–480°C, where rapid thermal degradation prevents further investigations. In the case of the 4-Hypp/4-Hybe 1:1 copolyester, the LC-phase extends over a temperature range of about 400°C. TGA measurements indicate beginning thermal degradation at temperatures between 350 and 380°C. |
