In-situ FTIR studies on the conformational changes of poly(ethy1ene terephthalate) (PET) films with different thermal histories, i. e., quenched from the melt and sub-T, 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, annealed samples. The magnitude and temperature of the abrupt changes of trans conformers were related with the temperature of sub-T, 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, annealing.
ABSTRACT:The effect of self-nucleation on the nonisothermal and isothermal crystallization behaviors of the segmented copolymer poly(ether ester), based on poly(ethylene glycol) as the soft segment and poly(ethylene terephthalate) as the hard segment was investigated by means of differential scanning calorimetry (DSC) and depolarization polarized light (DPL) techniques, respectively. The results demonstrated that selfnucleation could enhance the crystallization rate in both cases. The experimental conditions of the self-nucleation procedure studied by DSC were discussed in detail. The isothermal crystallization was analyzed by the Avrami equation, and the Avrami parameters were dependent on the melting temperature.
ABSTRACT:The mesophase transition and its kinetics of chitosan in the solutions of chitosan/dichloroacetic acid (DCA) were investigated by means of DSC and depolarized light intensity technique, respectively. The mesophase formation of chitosan in DCA involves nucleation and growth. The isothermal kinetics of mesophase formation from isotropic phase were described by Avrami using the equation with an exponent n close to 1, which suggests that the formation of chitosan mesophase is a process of instantaneous nucleation and one-dimensional rod-like growth in the temperature range investigated. This was confirmed by small angle light scattering Hv patterns of the mesophase.
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