Crystallization behavior and morphology of poly(ethylene‐co‐trimethylene terephthalate)s

Abstract

The melt crystallization behaviors and crystalline structures of poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate), and poly(ethylene‐co‐trimethylene terephthalate) (PETT) were investigated with differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X‐ray diffraction at various crystallization temperatures (Tcs). The PETT copolymers were synthesized via the polycondensation of terephthalate with ethylene glycol and trimethylene glycol (TG) in various compositions. The copolymers with 69.0 mol % or more TG or 31.0 mol % or less TG were crystallizable, but the other copolymers containing 34–56 mol % TG were amorphous. The DSC isothermal results revealed that the addition of a small amount of flexible TG (up to 21 mol %) to the PET structure slightly reduced the formation of three‐dimensional spherulites. A greater TG concentration (91–100%) in the copolyesters changed the crystal growth from two‐dimensional to three‐dimensional. The DSC heating scans after the completion of isothermal crystallization at various Tcs showed three melting endotherms for PET, PETT‐88, PETT‐84, and PETT‐79 and four melting endotherms for PETT‐9 and PETT. The presence of an additional melting endotherm could be attributed to the melting of thinner and imperfect copolyester crystallites. Analyses of the Lauritzen–Hoffman equation demonstrated that PETT‐88 had the highest values of the product of the lateral and folding surface free energies, and this suggested that the addition of small amounts of flexible trimethylene terephthalate segments to PET disturbed chain regularity, thus increasing molecular chain mobility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4255–4271, 2004

Sequence distribution, crystallization and melting behavior of poly(ethylene terephthalate-co-trimethylene terephthalate) copolyesters

“…4 also prove that the PET/PTT copolyesters containing 71, 60 or 50 mol% of 3G are crystallizable. This result is different from that reported by Smith et al [9], Ponnusamy, Balakrishnan [10,11], and Wu, Lin [14]. It might come from the low molecular weight [10,11] and the pre-melting conditions.…”

“…It is noted that one additional minor endotherm located in the high temperature side. One additional endotherm was also reported by Wu and Lin [14] for PTT and PET/PTT copolyester containing 91.4 mol% PT using conventional DSC. This phenomenon was observed only when these two polyesters were crystallized at lower T c 's and it was explained as the fusion of recrystallized crystallites with different stabilities.…”

“…3B). The same reason can explain the amorphous behavior of the copolyester with 56.5 mol% 3G [14] because the premelting condition of 40 8C above T m and 20 min was too high and too long for the copolyesters with close contents of ET and PT.…”

“…Up to now, the synthesis and characterization of poly(ethylene terephthalate-co-trimethylene terephthalate) (PET/PTT) copolyesters were reported in a few articles [9][10][11][12][13][14]. Most of these copolyesters were crystallizable, but some were amorphous depending on the compositions [9][10][11]13,14].…”

“…It was found that the copolymers containing 32.8 mol%%3G%39.3 mol% were amorphous, whereas the copolymers with 46, 58 and 78 mol% of 3G were crystallizable. Wu and Lin [14] mentioned that the amorphous copolymers contained 34-56 mol% of 3G which covers both ranges of 33-39 mol% [13] and 40-50 mol% [9] of 3G. In this study, 13 C NMR was used to determine the composition and the sequence distribution of the PET/PTT copolyesters.…”