摘要:

Thermally stimulated current (TSC) experiments have been performed on pullulan films in order to clarify the relation between the chemical structure and dielectric properties. These complex modes have been experimentally resolved into “elementary” processes characterized by relaxation times obeying Arrhenius equations: The corresponding activation energies, Eihave been measured.

ISSN:0022-2348    

DOI:10.1080/00222348308245756

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

When mixtures of poly(ester carbonate) (PEC) and poly(ethylene terephthalate) (PET) containing up to two-thirds of the latter are melt extruded, they produce a single-phase amorphous “alloy.” This alloy is characterized by a sharp, single, composition-dependent glass transition temperature, Tg. When annealed below Tg, the alloy remains unaltered, but when annealed above its Tg, the alloy separates into minute pure-PET crystallites and an amorphous PEC/PET phase. The thermal and dynamic mechanical behavior, crystallization kinetics, and SAXS patterns all strongly suggest the PEC-rich alloys to be solid solutions in which the PET molecules are dispersed individually or in small aggregates containing only a few PET molecules each. Calculations of the interaction parameter and assumed interfacial layer thickness tend to support this suggestion. Use of appropriate solvents allows one to selectively dissolve the PEC and recover from the alloys both PET and PEC in the original purity and molecular weights. Diffusion constants of PET molecules through the amorphous alloys were obtained from studies of PET crystallization above Tgof the alloys. The magnitude of the constants are in the range of expectation. The mechanical properties of the amorphous alloys in the glassy state do not deviate greatly from simple additivity of the respective properties of the parent polymers. However, the melt viscosity of the PEC-rich alloys and their plateau modulus above T show drastic decreases from straight additivity. A qualitative, but not quantitative, explanation of these observations is offered.

ISSN:0022-2348    

DOI:10.1080/00222348308245757

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The birefringence of solvent-cast atactic polystyrene films was measured as a function of annealing temperature. The birefringence was found to disappear at a temperature which corresponds to the liquid-liquid transition, as measured by differential scanning calorimetry. It is concluded that this experiment is a proof of the molecular origin of the liquid-liquid transition.

ISSN:0022-2348    

DOI:10.1080/00222348308245758

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor