EFFECT OF THE BLOCK LENGTH ON THE DEFORMATION-BEHAVIOR OF POLYETHERESTERS AS REVEALED BY SMALL-ANGLE X-RAY-SCATTERING

The SAXS behavior of six selected samples of a set of polyetherester thermoplastic elastomers based on polybutylene terephthalate (PBT) as hard segments and polyethylene glycol (PEG) as soft segments in ratios 41/59, 49/51, 57/43, and 75/25 wt. % was studied under and without stress. Three different glycols with M(n)BAR of 320, 890, and 1400 with a very narrow polydispersity range (M(w)BAR/M(n)BAR = 1.3) were used. The samples were drawn 5.5 x and thereafter annealed with fixed ends at one and the same undercooling. Three different types of long spacing were observed. The first one, L, rises proportionally to the deformation up to epsilon = 75-100%, where it reaches a value of L(max). The second one, L' usually close to the initial long spacing Lo, is observed for deformations larger than 100%. The third one, L(rel), appears after removal of the external stress and subsequent relaxation. The fractions of intra- and interfibrillar amorphous material are calculated on the basis of the DSC degree of crystallinity, the observed L and the lamella thickness l(c) (from WAXS data). In contrast to homopolymers, the interfibrillar amorphous material fraction is very large (30-80%). A fairly good agreement between the measured L(max) values and those calculated on the basis of the segments length is obtained. The appearance of a second long spacing could be explained assuming microfibril relaxation and/or formation of additional layers of hard segments in the originally amorphous phase during elongation. The available data are not sufficient to show preference for one of the two models.