Jignesh P. Sheth

Solid state structure–property behavior of semicrystalline poly(ether-block-amide) PEBAX® thermoplastic elastomers

Abstract The solid state structure–property behavior was investigated of a series of poly(ether- block -amide) PEBAX ® thermoplastic elastomers based on nylon 12 and poly(tetramethylene oxide) with varying hard segment content. Particular emphasis was placed on better defining the morphological features of this entire series of commercially available materials. Compression molded and solution cast samples were studied by the techniques of DMA, DSC, WAXS, SAXS, AFM, SALS and stress–strain response. The strain-induced crystallization behavior of the soft polyether (PE) segments was also investigated. All samples exhibited a microphase separated morphology over a broad temperature range. As expected, an increase in the interconnectivity of the polyamide hard phase was greatly controlled by the polyamide (PA) content. Due to the crystallization of the PA hard segment, the formation of PA lamellar crystals was noted in both melt and solution cast films. At the higher PA contents, a distinct spherulitic superstructure was also observed but this form of morphological texture was diminished as the PE soft segment content increased. Limited studies of the deformation/recovery behavior of the spherulitic superstructure provided further information concerning the interaction between the hard and soft segments.

Structure-property behavior of new segmented polyurethanes and polyureas without use of chain extenders

Abstract New novel segmented polyurethane and polyurea copolymers have been synthesized without chain extenders and the structure-property behavior of these systems has been investigated. It is shown that by the proper choice of diisocyanate and its symmetry, one can obtain highly microphase separated systems without chain extenders and that the materials also display useful mechanical behavior. In particular, it is shown that due to the bidentate hydrogen bonding achieved in the segmented ureas, a significant modulus “service temperature window” is also obtained. It is also verified that not only can strong microphase separation be obtained with low weight fraction hard segment content (14%) but that the hard phase, which is comprised of monodisperse “single molecule” units, also displays a percolated thread-like structure throughout the dominant soft segment material — the latter being based on ca. 1000g/mol polytetramethylene oxide.