The morphological behavior of a series of well-defined A2B simple graft or “Y” architecture block copolymers is characterized via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). This model architecture is formed by grafting a polystyrene block onto the center of a polyisoprene backbone. The volume fraction windows in which specific strongly segregated microphase-separated morphologies are observed are shifted to higher volume fractions of the PS graft material than in the corresponding linear diblock copolymers. These findings are in good agreement with recently calculated theoretical phase behavior for simple graft, A2B, block copolymers. However, a new morphology, not found in neat linear diblock copolymers, is also observed. This A2B material is microphase separated into wormlike micelles but not ordered on a lattice. This morphology is found at high PS graft volume fraction (φs = 0.81), where the two PI chains per molecule are initially forced to the concave side of the PS/PI interface.
The synthesis, morphology, and dynamics of block copolymers in various states is reviewed. Living polymerization techniques used to prepare well‐defined diblock, triblock, and starblock copolymers are first summarized. Then the phase behavior of block copolymers in the melt is discussed, based on experimental and theoretical work. The effect of confinement on block copolymers in thin films is then considered. The behavior of block copolymers in solution and applications resulting from micelle formation are also reviewed. The effect of crystallization on block copolymer morphology is also outlined. Finally, the competing effects of micro‐ and macrophase separation in blends of polymers containing block copolymers is described, along with compatibilization of immiscible polymers by block copolymers.
The phase behavior of diblock copolymers near the order-disorder transition is studied using transmission electron microscopy, small-angle neutron scattering (SANS) and dynamical mechanical spectroscopy. For a series of polyolefin diblocks with volume fraction, f1, of the block with the larger segment length in the range f1 = 0.63 - 0.75, we find that the transition from lamellae to hexagonally packed cylinder phases occurs via intermediate layered phases that are always characterized by in-plane hexagonal order. One class of diblock forms a hexagonally modulated lamellar (HML) phase, then a hexagonally perforated layer (HPL) phase upon heating from lamellae, while another class forms a modulated hexagonally packed cylinder phase from the HML phase. We attempt to rationalize this based on the differences in inter-layer ordering in the HML phase evidenced by SANS patterns. Detailed phase diagrams for the diblocks depend on molecular weight, and a conformational asymmetry parameter, which is discussed. These results are similar to those found in certain smectic liquid crystal polymorphs, suggesting an analogy between thermotropic liquid crystalline behavior and the intermediate layered phases of diblock copolymer melts
Cell dynamics simulations are a powerful tool to simulate kinetic processes in phase separating systems. Here we review the technique and its application to block copolymers. Its advantages and disadvantages compared to other simulation methods for block copolymer structure and dynamics are reviewed. Results on the dynamics of microphase separation and interface propagation, and on the rate of order‐order phase transitions are reviewed. The use of the method to model certain shear‐induced structural and flow effects is also summarised.
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