Abstract: In order to increase the glass transition temperature (T_g) of polyethylene terephthalate (PET) and broaden the application field of PET, poly (ethylene terephthalate-co-isosorbide terephthalate) (PEIT) was prepared by direct esterification with bio-based isosorbide (ISB) as the third monomer and self-made Ti-Al bimetallic coordination compound as catalyst.The structure and thermal properties of the copolyester were characterized by nuclear magnetic resonance, Fourier transform infrared spectrometer, differential scanning calorimeter, and thermogravimetric analyzer.The results show that the self-made catalyst has good catalytic activity for ISB. When adding less than 15% of ISB, the reaction rate can reach 90%, and the copolyester product with an intrinsic viscosity of about 0.65 dL/g can be quickly obtained. The intrinsic viscosity of the copolyester increased to about 1.20 dL/g after 1.5 h of melting post polycondensation, which indicates that the copolyester prepared by the titanium-based catalyst has strong chain growth ability during melt polycondensation. Increasing the proportion of ISB in the synthesis will reduce the intrinsic viscosity of the copolyester, but the crystallization temperature(T_c) of the copolyester will increase and the melting point(T_m) will decrease. There is a positive correlation between glass transition temperature (T_g) and the added ISB content. When the amount of ISB added reaches 20%, the T_g of the copolyester reaches 94.7 ℃, and the correlation calculation formula of T_g and ISB content is obtained by fitting.However, when the amount of ISB exceeds 15%, the polymer begins to transform into an amorphous polymer, but its thermal decomposition performance is not significantly affected.

Key words: copolyester, isosorbide, titanium catalyst, glass transition temperature

摘要： 为了提高PET的玻璃化转变温度(T_g),拓宽PET的应用领域,以生物基异山梨醇(ISB)作为第三单体,使用自制Ti-Al双金属配位催化剂,通过直接酯化法制备了聚对苯二甲酸乙二醇-co-对苯二甲酸异山梨醇酯(PEIT)共聚酯。利用核磁共振仪、傅里叶红外光谱仪、差示扫描量热仪、热重分析仪等表征了共聚酯的结构和热性能。结果表明:自制催化剂对于ISB具有较好的催化活性,在加入15%以内ISB时其反应率可达90%,可快速得到特性黏度约为0.65 dL/g左右的共聚酯产物。共聚酯经液相增黏反应1.5 h后其特性黏度上升至约为1.20 dL/g,说明钛系催化剂制备的共聚酯在熔融缩聚时的链增长能力强。合成时提高ISB比例会使共聚酯的特性黏度降低,结晶温度(T_c)上升,熔点(T_m)下降。玻璃化转变温度(T_g)与加入的ISB含量成正相关,当ISB加入量达到20%时,共聚酯的T_g达到94.7 ℃,并拟合得出T_g和ISB含量相关计算公式。而ISB加入量超过15%时聚合物开始转变为无定型聚合物,但对其热分解性能没有显著影响。

关键词: 共聚酯, 异山梨醇, 钛系催化剂, 玻璃化转变温度