Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
The dynamic mechanical properties of polyester and polyether urethane block polymers have been investigated at four frequencies (3.5, 11, 35 and 110 Hz) in the temperature range of - 150 to 200°C. The existence of a two phase structure was demonstrated in these systems by the observation of two major transition regions corresponding to (1) the glass transition temperature (Tg) of the ester or ether soft segments, and to (2) the softening temperature of the aromatic-urethane hard segments. Several secondary relaxations were observed in addition to the two major relaxations. It was possible to assign molecular mechanisms to each of these relaxations. All relaxation phenomena were greatly influenced by the molecular weight of the prepolymer, weight percent of hard segments, and thermal history. An increase in the molecular weight of the prepolymer above 1,000 at constant hard segment content resulted in a semi-crystalline material, which possessed a lower Tg for the macroglycol segments. Annealing to enhance crystallinity increased the Tg of the soft segments, consistent with the usual observation in semicrystalline homopolymers. These findings suggest that the relaxation mechanisms of polyurethane block polymers are not only influenced by the degree of crystallinity, but also by the nature of the domain structure.
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