New polymer syntheses 16. LC‐copolyesters of 3‐(4‐hydroxyphenyl) propionic acid and 4‐hydroxy benzoic acids

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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.