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Surface segregation behavior in miscible polymer blend thin film of poly(4-trimethylsilylstyrene)(PT)/polyisoprene (PI) was investigated as a function of temperatures on the basis of contact angle and neutron reflectivity measurements. For all temperatures employed, PT, which is a lower surface free energy component, is segregated at the surface of the blend film due to the requirement for minimizing the total free energy of the system. A concentration profile near the blend film surface is in good agreement with the mean-field prediction at 373 K and 393 K, being much lower than the lower critical solution temperature (LCST) for the blend in bulk. It was confirmed that decay length, ξ, and surface excess amount, z*, increase with increasing temperature. On the other hand, a concentration fluctuation in the internal region becomes remarkable at 453 K, even below the LCST in bulk. Thus, it is concluded that a concentration fluctuation in PT/PI blend thin film below the LCST is induced by the surface segregation of PT component in blend thin film.

The phase behavior of the newly found miscible polymer blends poly(4-trimethylsilylstyrene) and polyisoprene was investigated with optical microscopy (OM) and also with differential scanning calorimetry (DSC), while the degree of polymer−polymer interaction was evaluated with small-angle neutron scattering (SANS). The blends with homogeneous one phase at various compositions turned into two phases by heating, showing a lower critical solution temperature (LCST) type phase diagram with a critical temperature of 172 °C if the degree of polymerization is ca. 370. The blend gave a single glass transition temperature below the LCST, and the interaction parameter χ was represented as a function of temperature T according to the relationship χ = 0.027 − 9.5/T.

Three poly(4-trimethylsilylstyrene)-block-polyisoprenes (TIs), the molecular weights of which were 82,000, 152,000 and 291,000 (TI-82K, TI-152K, and TI-291K), were synthesized by sequential anionic polymerizations. The component polymers were a miscible pair that presented a lower critical solution temperature phase diagram if blended. The TI phase behavior was investigated with transmission electron microscopy. The order-disorder transition could be observed at a temperature between 200 °C (the ordered state) and 150 °C (the disordered state) for the block copolymer TI-152K. The block copolymer TI-82K presented the disordered state at 200 °C, whereas TI-291K was in the ordered state at 150 °C. With the Flory-Huggins interaction parameter between poly(4-trimethylsilylstyrene) and polyisoprene, which was evaluated by small-angle neutron scattering for the block copolymers, the TI phase behavior could be reasonably explained by mean-field theory.

Compositional profiles of bilayer films in the direction normal to the interfaces have been investigated by neutron reflectivity measurements and analyzed with mean field theory. The bilayer films were prepared with poly(4-trimethylsilylstyrene) (PTMSS) and polyisoprene (PI), which constitute a miscible polymer pair and whose blends show phase separation at the lower critical solution temperature (LCST) by heating. Because we can accurately control the degree of polymerization of component polymers and can adjust the Flory-Huggins interaction parameter, X, with the temperature, T, according to the relationship X = 0.027-9.5/T, the phase behavior and the interfacial structure of PTMSS and PI are predictable by mean field theory. When the bilayer films of PTMSS and PI were set at 90 C, which is a temperature below the LCST, diffusion at the interface was observed, and the original interface disappeared in several hours; this supports the idea that the polymer pair is miscible. No clear interfaces were identified below the LCST, whereas broad interfaces, compared with that of the strong segregation pairs, were observed above the LCST. The compositions of each layer are consistent with that of the coexisting phase in the polymer blends, and the interfacial widths agree well with the theoretical prediction considering the effect of capillary waves. In addition, all annealed films have a thin surface layer of PTMSS corresponding to surface segregation induced by the lower surface energy of PTMSS (with respect to that of PI). Thus, the interfacial profiles of PTMSS/PI bilayer films have been totally prospected in the framework of mean field theory.