REVERSIBLE MORPHOLOGICAL-CHANGES IN POLY(ETHER ESTER) THERMOPLASTIC ELASTOMERS DURING DEFORMATION AS REVEALED BY SMALL-ANGLE X-RAY-SCATTERING

The scattering behavior of undrawn and drawn annealed bristles of ther moplastic elastomers with conventional and higher molecular weight bas ed on poly(butylene terephthalate) as hard segments and poly(ethylene glycol) as soft segments in a ratio of 49/51 wt.% is studied. Small-an gle x-ray scattering (SAXS) measurements with an area detector are car ried out on single bristles under or without applied stress and with d eformations up to 300%. At low macrodeformations (epsilon less-than-or -equal-to 30-40%) the morphology of the predrawn samples represents as semblies of parallel crystalline lamellae positioned perpendicular to the stretching direction. These morphological characteristics remain u nchanged within the entire deformation range (up to epsilon = 300%) fo r the predrawn samples of lower molecular weight. For the initially un drawn sample of larger molecular weight reversible orientation and dis orientation of the crystallites (microdomains) is established in the s ame deformation range. Common morphological features are found for the predrawn and undrawn samples with increased molecular weight at mediu m (epsilon = 50-150%) and high (epsilon = 150-300%) deformation ranges . For both samples in an unloaded relaxed state the x-ray patterns can be explained by a zig-zag arrangement of crystalline lamellae, i.e., the microdomains are inclined to the stretching direction. After loadi ng, the microdomains transform to a position perpendicular to the stre tching direction. This observed morphological transition is found to b e reversible and becomes more pronounced with progressing deformation. It is suspected to contribute to reversible macrodeformations of ther moplastic elastomers in many cases and may be related to the large amo unt of tie-molecules created during solid-state reactions in those mat erials.