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

The morphologies formed by block copolymers with a double-graft, H or S2IS2 architecture were investigated using transmission electron micro scopy (TEM) and small angle neutron scattering (SANS). Here S and I re present blocks of polystyrene and polyisoprene, respectively. These ma terials were synthesized using anionic polymerization and chlorosilane Linking, and they were characterized using size exclusion chromatogra phy, membrane osmometry, and low-angle laser light scattering. This ch aracterization work confirmed the desired molecular architectures and narrow molecular weight distributions. The results of morphological ch aracterization indicate that one can understand complex grafting archi tectures by decomposing them into fundamental building blocks, which a re taken as the component single graft structures out of which the lar ger structure is constructed. We propose rules for dividing structures into these components, which we call constituting block copolymers. T he morphological behavior of the more complex architecture is approxim ately equivalent to that of the constituting block copolymer structure . Through the use of the constituting block copolymers we map the expe rimentally determined morphological behavior of the H architecture ont o the morphology diagram calculated by Milner for miktoarm stars [Macr omolecules 27, 2333 (1994)]. Mapping the H architecture onto the morph ology diagram in this way produces general agreement between experimen tal results and the model. However, it is found that in the case of th e H architecture, as well as in previously published results for I2S a nd I3S miktoarm star materials, that the morphology diagram slightly o verestimates the amount of shift in the order-order transition lines p roduced by asymmetry in molecular architecture. This overestimation in the theory is attribute to a junction point localization effect which was neglected in Milner's calculation. (C) 1997 American Institute of Physics.