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摘要
Bulk poly(ethylene terephthalate) PET has been reorganized both morphologically and conformationally by processing from its inclusion complex (IC) formed with gamma-cyclodextrin (CD). In the narrow channels of its gamma-CD-IC crystals the included guest PET chains are isolated from neighboring PET chains and the ethylene glycol (EG) units adopt the highly extended g+/-tg-/+ kink conformations, whose cross-sectional diameters are similar to80% of the diameter of the fully extended, all-trans crystalline PET conformer, though they are nearly (similar to95%) as extended. When the highly extended, unentangled guest PET chains are coalesced from their gamma-CD-IC crystals by exposure to hot water, host gamma-CDs are removed and the PET chains are presumably consolidated into a bulk sample with a morphology and constituent chain conformations not normally found in PET samples solidified from their randomly coiling, possibly entangled, disordered melts and solutions. Observations by polarized light and atomic force microscopies provide visual evidence for widely different semicrystalline morphologies developed in coalesced and as-received PETS when crystallized from their melts, with possibly chain extended, small crystals and spherulitic, chain-folded, large crystals, respectively. DSC observations reveal that coalesced PET is rapidly crystallizable from the melt, while as-received PET is slow to crystallize and is easily quenched into a totally amorphous sample. Analyses of C-13-NMR data strongly indicate that the PET chains in the noncrystalline regions of the coalesced sample remain predominantly in the highly extended kink conformations, with g+/-tg-/+ EG units, which are required by their inclusion into PET-gamma-CD-IC crystals, while the predominantly amorphous PET chains in the as-received sample have high concentrations of gauche+/- -CH2-CH2- and trans -O-CH2-,-CH2-O- EG bond conformations. C-13-NMR T-1(C-13) and T-1rho(H-1) relaxation studies show no evidence of a glass transition for coalesced PET, while the as-received sample shows abrupt changes in both the MHz [T-1(C-13)] and kHz [T-1rho(H-1)] motions at T similar to T-g. Preliminary observations of differences in their macroscopic properties are attributed to the very different morphologies and conformations of the constituent chains in these PET samples. Apparently the kink conformers in the noncrystalline regions of coalesced PET are at least partially retained for extended periods even in the melt and are rapidly crystallized upon cooling.
- 出版日期2004-2-1
