Studies On The Effects Of Diacid With Long Carbon Chain On PBT's Crystallization And Melting Behavior

Poly(butylene terephthalate) (PBT), and the copolymers poly(butylene terephthalate-co-dodecandioicate) (PBTD), poly(butylene terephthalate-co-tridecandioicate) were prepared by the directed esterification and polycondensation of 1,4-butanediol (BDO), terephthalic acid (TPA), dodecandioic acid (DC-12) or tridecandioic acid (TC-13) with Ti(OBu)4 as the catalyst. The polymers were assigned as PBT, PBTD-5, PBTD-15, PBTT-5 and PBTT-15, respectively.The molecular structure and molecular weight distribution of PBT, PBTD-5, PBTD-15, PBTT-5 and PBTT-15 were characterized and tested by 1H-NMR and gel permeation chromatogram (GPC). The melting behavior and isothermal crystallization kinetics of the samples was monitored by differential scanning calorimetry (DSC). Equilibrium melting temperatures are estimated by the Hoffman-Weeks equation. The isothermal crystallization data are described by Avrami equation and the Avrami exponent n range from 2.63 to 2.97, suggesting that the addition of dodecandioic acid and tridecandioic acid do not affect the geometric dimension of the polymer crystal growth and the isothermal crystallization follows two-and three-dimensional growth mechanism. A comparison of 1/t1/2 values at equivalent supercooling clearly shows that a smaller amount of diacid with long carbon chain (5 mol%) in PBTD will enhance crystallization of the polymer, but a larger amount of diacid (15 mol%) will hinder crystallization of the polymer. The Avrami equation modified by Jeziorny and the equation deduced by Mo were used to describe the behaviors of the nonisothermal crystallization, respectively and the the effect of cooling rate on the crystallization rate is also discussed.