Stoichiometric Effects on Nanostructures of Block- and Graft-Type Supramacromolecules via Acid-Base Complexation

We report a systematic study on nanophase-separated structures from block- and graft-type supramacromolecules via acid-base complexation, where supramacromolecules are termed as supramolecules composed of a pair of macromolecules with complementary noncovalent bonding moieties. Block- or graft-type supramacromolecules were built up by blending component polymers, that is, sulfonic acid-terminated polystyrene (PS-SO3H, M-n = 19 k) or polystyrene-block-poly(4-styrenesulfonic acid) (PS-P(SSO3H), M-n =23k) with primary amine-terminated polyisoprene (PI-NH2, M-n = 17 k). Self-assembled nanostructures of the blends were confirmed complementarily by transmission electron microscopy and small-angle X-ray scattering. At larger acid[base molar ratio, the blends show comparatively ordered nanophase-separated structures without macrophase-separated large PS domain, Morphological transition controlled by composition has occurred in the blends of PS-P(SSO3H)/PI-NH2 as ordinary block copolymers show, though the blends of PS-SO3H/PI-NH2, showed macrophase separation at excess ratio of PI-NH2 to PS-SO3H. The difference in composition dependence of morphology between two blend series is resulted from stoichiometric effects of sulfonic acid vs amine. Therefore, PS-P(SSO3H) is more useful to build up various supramacromolecular complexes with PI-NH2 than PS-SOH just by changing the molar ratios of component polymers, that is, multiple noncovalent bonding can be found more advantageous, resulting in conforming graft-type supramacromolecules, not a block-type supramacromolecule from PI-NH2 and PS-S03H.