Pet/phb, The Synthesis And Characterization Of Liquid Crystal Copolyesters

PET/PHB thermotropic liquid-crystal copolymers are promisingly and widely used for their high stiffness and modulus, heat resistance, low coefficient of expansion, excellent melt processability and unique mechanical strength. However, the copolymers prepared by conventional techniques were found to be block ones due to self-polymerization of PABA. The structure of the copolymers was hard to control. In this work, PABA and PET were used to synthesize PET/PHB copolymers by using the two-step method. Thereafter, PHB、PET、AC2O were used to synthesize PET/PHB copolymers by using the one-step method on the basis of the results from the two-step method. The experimental results showed that the intrinsic viscosity (IV) of PET/PHB copolymers synthesized by two-step method increased and then decreased with increasing PABA content. The Ⅳ,0.790dL/g, was the highest when the PHB mole fraction was60%. It was found that the nematic liquid crystalline texture appeared clearly when the mole fraction of PABA was between50%and70%. PET/PHB copolymer was also synthesized by using the one-step method. It was found that the IV of PET/PHB was dependent on the content of PHB and catalyst, reaction temperature and vacuum degree. The IV of PET/60PHB copolymer,0.650dL/g, was the highest when the temperature was290℃, the vacuum degree below100Pa and the mole fraction of catalyst, i.e., catalyst0.037mol%. Adding excess acetic acid to the reaction system could inhibit the self-polymerization of PABA and promote the copolymerization of PABA and PET. PET/60PHB copolymers with the IV of0.905dL/g can be synthesized when the adding excess acetic acid was7mol per mole PHB.