| Research Abstract |
The purpose of this study was to clarify the relationships between the pressure effects on the miscibility and phase diagrams of polymer alloys such as polymer blends and block copolymers and the molecular structures of the constituent polymers. Small-angle neutron scattering measurements were performed by using the small-angle neutron scattering instrument (SANS-U) of Institute of Solid State Physics, the University of Tokyo, equipped on the research reactor JRR-3M at Japan Energy Research Institute in Tokai (20 MW). We designed and constructed a high pressure cell equipped with sapphire windows for the SANS measurements and investigated the pressure effects on the miscibility and order-disorder transition of deuterated polybutadiene-block-polyisoprene diblock copolymers (DPB-HPI) with two different microstructures. Prior to the SANS measurements, we synthesized two DPB-HPI's, one rich in 1,4-linkages (Sample A) and the other rich in 1,2-linkages (vinyl-type, Sample B), both with narr
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ow molecular-weight distribution by living anionic polymerization. Sample A exhibited the LCST-type phase behavior, i.e., the scattering and, therefore, the amplitude of the concentration fluctuation increased with temperature, while the scattering from Sample B changed little but slightly decreased with temperature suggesting the UCST-type phase behavior. The order-disorder transition temperature estimated from the appearance of the second-order scattering peak increased almost 35C by applying the pressure of 80 MPa, which is twice as large as that reported for the UCST-type polystirene-block-polyisoprene diblock copolymer by Hajduk et al.by small-angle X-ray scattering measurements, but the effect of pressure on the miscibility is opposite. On the other hand Sample B did not show significant pressure dependence. These results suggest that the pressure effects on the miscibility of polymers depend on the molecular structures, since the miscibility of polymers depends on the change of the free volume on mixing and the pressure dependence of the free volume changes greatly with the molecular structures. Less
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