Closed-loop phase behaviour in block copolymers.
Closed-loop phase diagrams are known in systems with specific intermolecular interactions. In weakly interacting systems, however, such behaviour has never been observed. Here, diblock copolymers formed from polystyrene covalently linked to poly (n-pentylmethacrylate), P(S-b-nPMA), which have only weak segmental interactions, are shown to exhibit a closed-loop phase behaviour over a narrow range of molecular weight. The endothermic transitions from the disordered to ordered and back to the disordered state, as a function of increasing temperature, are dominantly entropic in origin. The morphology and rheological properties of P(S-b-nPMA) undergo characteristic changes at the transitions. Whereas the disorder-to-order transition temperature increases with decreasing molecular weight, the order-to-disorder transition temperature decreases. At a limiting molecular weight, the closed-loop vanishes and no ordering occurs. These findings provide quantitative insight into an elusive transition in weakly interacting multicomponent systems.
Ryu
Du Yeol
DY
Department of Chemical Engineering and Polymer Research Institute, Pohang University of Science and Technology, Kyungbuk 790-784, Korea.
Jeong
Unyong
U
Kim
Jin Kon
JK
Russell
Thomas P
TP
D018360:Crystallography, X-Ray / Q000379:methods*; D004548:Elasticity; D005246:Feedback; D006358:Hot Temperature; D046911:Macromolecular Substances; D008422:Materials Testing / Q000379:methods*; D008854:Microscopy, Electron / Q000379:methods; D008968:Molecular Conformation; D008970:Molecular Weight; D017711:Nonlinear Dynamics; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*; D012212:Rheology / Q000379:methods; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D033081:Shear Strength; D013314:Stress, Mechanical
D046911:Macromolecular Substances; D011108:Polymers; D011109:Polymethacrylic Acids; D011137:Polystyrenes; C030613:polymethacrylic acid