LONG SPACING IN POLYBLOCK POLY(ETHER ESTER)S - ORIGIN AND PECULIARITIES

Poly(ether ester)s (PEE) based on poly(butylene terephthalate) (PBT) as hard segments and poly(ethylene glycols) (PEG) with different molecular weight as soft segments are studied by means of WAXS and SAXS in the drawn and undrawn state after annealing at various temperatures (T(a)). The repeatedly reported strong increase of the long spacing L with T(a) is confirmed once again. In the same time the directly measured by WAXS crystallite size of PBT remains insensitive to T(a) and the increase of L with T(a) is the stronger, the higher the PEG content. It is concluded therefore that the rise in L is due to the expansion of the amorphous intercrystalline layers rather than to crystal thickening, the latter being the case of semicrystalline homopolymers. The observed much stronger increase of L with T(a) in undrawn samples than in drawn ones is explained by melting of less perfect crystallites at higher T(a) and dephasing processes in the amorphous regions. The conclusions drawn seem to be valid for other segmented polyblock copolymers and suggest some specific features of the block copolymers in comparison to homopolymers.