Small-angle X-ray scattering and rheological studies on the ordering process of cylindrical microdomains in a polystyrene-block-polyisoprene copolymer

Abstract

Ordering of cylindrical microdomains in a low molecular weight polystyrene-block-polyisoprene (SI diblock) copolymer was investigated using small-angle X-ray scattering (SAXS) and rheology. The SI diblock copolymer was found to have (i) hexagonally packed cylindrical microdomains of polystyrene phase in a polyisoprene matrix in the ordered state, and (ii) an order-disorder transition temperature T(ODT) Of Ca 90 degrees C. TO investigate the ordering process from the disordered state, a specimen was quenched rapidly from the disordered state to a temperature below its T(ODT), and then the time evolution of the SAXS intensity and dynamic moduli (G' and G ") (i.e. the ordering process) was monitored. We have found that the ordering process in the block copolymer, when quenched to an ordered state close to its T(ODT). takes place very slowly. Specifically, we found that when a specimen was quenched rapidly from 100 degrees C (10 degrees C above T(ODT)) to 80 degrees C (10 degrees C below T(ODT)), the ordering into the hexagonally packed cylinders occurs via a nucleation-growth process and the attainment of the equilibrium microdomain morphology took about 6 h when monitoring G' and G " and about 8 h when monitoring the SAXS intensity. (C) 1997 Elsevier Science Ltd. All rights reserved.