MORPHOLOGIES OF MICROPHASE-SEPARATED A(2)B SIMPLE GRAFT-COPOLYMERS

The morphological behavior of a series of well-defined A(2)B simple gr aft or ''Y'' architecture block copolymers is characterized via small- angle X-ray scattering (SAXS) and transmission electron microscopy (TE M). This model architecture is formed by grafting a polystyrene block onto the center of a polyisoprene backbone. The volume fraction window s in which specific strongly segregated microphase separated morpholog ies are observed are shifted to higher volume fractions of the PS graf t material than in the corresponding linear diblock copolymers. These findings are in good agreement with recently calculated theoretical ph ase behavior for simple graft, A(2)B, block copolymers. However, a new morphology, not found in neat linear diblock copolymers, is also obse rved. This A(2)B material is microphase separated into wormlike micell es but not ordered on a lattice. This morphology is found at high PS g raft. volume fraction (phi(s) = 0.81), where the two PI chains per mol ecule are initially forced to the concave side of the PS/PI interface.