PI-SHAPED DOUBLE-GRAFT COPOLYMERS - EFFECT OF MOLECULAR ARCHITECTURE ON MORPHOLOGY

The morphologies formed by block copolymers with a double-graft, pi or (S,I)I'(S,I) architecture were investigated using transmission electr on microscopy (TEM) and small angle neutron scattering (SANS). Here S and I represent blocks of polystyrene and polyisoprene, respectively. These materials were synthesized using anionic polymerization and chlo rosilane linking, and they were characterized using size exclusion chr omatography, membrane osmometry, and low-angle laser light scattering. This characterization work confirmed the desired molecular architectu res and narrow molecular weight distributions. The results of morpholo gical characterization indicate that one can understand complex grafti ng architectures by decomposing them into fundamental building blocks, which are taken as the component single-graft structures out of which the larger structure is constructed. We propose rules for dividing st ructures into these components, which we call constituting block copol ymers. For the a double-graft architecture, the constituting block cop olymer is an asymmetric single-graft block copolymer. The morphologica l behaviour of the more complex double-graft architecture is approxima tely equivalent to that of the constituting single-graft block copolym er. Through the use of the constituting block copolymers we map the ex perimentally determined morphological behaviour of eight materials wit h a architecture onto the morphology diagram calculated by Milner for miktoarm stars. As in our previous study of asymmetric single-graft bl ock copolymers, the asymmetry of the graft location along the backbone requires a generalization of the molecular asymmetry parameter, epsil on, used in the calculated morphology diagram. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.