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The effects of physical ageing on conformational changes of poly(ethylene terephthalate) in the glass transition region
Author(s) -
Qian Renyuan,
Shen Deyan,
Sun Fuge,
Wu Liheng
Publication year - 1996
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.1996.021970425
Subject(s) - endothermic process , differential scanning calorimetry , conformational isomerism , glass transition , annealing (glass) , ethylene , poly ethylene , activation energy , materials science , fourier transform infrared spectroscopy , population , polymer chemistry , analytical chemistry (journal) , chemistry , polymer , crystallography , thermodynamics , molecule , chemical engineering , composite material , organic chemistry , demography , physics , catalysis , adsorption , sociology , engineering
In‐situ FTIR studies on the conformational changes of poly(ethylene terephthalate) (PET) films with different thermal histories, i. e., quenched from the melt and sub‐ T g annealed at different temperatures, were carried out while increasing the temperature through the glass transition region. The temperature dependencies of the infra‐red spectra showed that incremental changes of the population of trans conformers in the quenched sample are gradual, while rather abrupt changes occur in the sub‐ T g annealed samples. The magnitude and temperature of the abrupt changes of trans conformers were related with the temperature of sub‐ T g annealing. An energy difference of 28.6 J/g between the trans and gauche conformational states was measured by the infra‐red spectroscopic method. The energy absorbed during the abrupt conformational change represents only part of the energy of the endothermic peak observed by differential scanning calorimetry. The results are explained in terms of the formation of new cohesional entanglements during sub‐ T g annealing.