Citation: WANG Dexi, R. E. Lyon, R. J. Farris. MULTIPLE MELTING TRANSITIONS IN POLYURETHANE-UREA ELASTOMERS UNDER EXTENSION[J]. Chinese Journal of Polymer Science, ;1986, 4(3): 274-283. shu

MULTIPLE MELTING TRANSITIONS IN POLYURETHANE-UREA ELASTOMERS UNDER EXTENSION

Received Date: 2 March 1986

Two melting transitions were observed in linear segmented polyurethane-urea elastomers underextension using thermal, mechanical and X-ray diffraction techniques, and the results are compared.These data indicate both strain-induced and temperature-induced crystallization in the stretchedclastomers, which may result from two different types of crystallites with different melting tempera-tures. These have been assigned as type 1 appearing around 60℃, and type 2 around 30℃. The type 1 crystallization can be induced by stretching at room temperature to large strain,and is mechanically reversible,but the type 2 crystallization is mainly induced by cooling below its crystallization temperature.These two crystalline structures are interchangeable under suitable conditions.At elongations greater than 300%,the low temperature peak observed on fusion thermograms disappears or combines with the high temperature peak.When the temperature of the samplc is over the melting point of the type 1 crystal,irreversible melting occurs and only the type 2 crystal develops on cooling.The results of stress-strain and stress hysteresis experiments at different temperatures indicate the relative importance of strain-induced and temperature-induced crystallization on the mechanical properties of these materials.
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