Reversible stress-induced crystallization of the soft phase in polyblock thermoplastic elastomers under uniaxial tension

For microphase-separated polyblock thermoplastic elastomers composed of alternating soft [poly(tetramethylene oxide) with M = 2 x 10(3))] and hard [poly(butylene terephthalate), polyamide-12, diphenylmethane diisocyanate] blocks, the stress-induced reversible crystallization of poly(tetramethylene oxide) was studied by the methods of deformation calorimetry and wide-angle X-ray diffraction. The presence of the pure soft-block phase allows its reversible stress-induced crystallization. The effect of the tensile strain and temperature on the stress-induced crystallization of poly(tetramethylene oxide) was studied. Above the glass transition temperature of hard blocks, the stress-induced crystallization of poly (tetramethylene oxide) does not occur. Intramolecular components of energy effects were assessed by thermodynamic analysis of the deformation process. A comparative quantitative estimation of the maximum degree of crystallinity of poly(tetramethylene oxide) upon its stress-induced crystallization was performed. In poly(ether urethane), the stress-induced crystallization of poly (tetramethylene oxide) is fully reversible. However, in the poly(ether ester) thermoplastic elastomer and especially in poly(ether amide), even though reversible deformations are localized in amorphous regions, poly(tetramethylene oxide) crystals are partially preserved after the stress release.