We report the morphology and phase behaviors of binary blends of polystyrene-block-polyisoprene (SI) copolymers, which were studied by a small-angle X-ray scattering (SAXS) technique. The neat SI copolymers employed in this study have almost the same molecular weights but different volume fractions of polystyrene block (φPS = 0.26 and 0.65). Blends with various overall volume fractions of polystyrene block ( ), ranging from 0.41 to 0.60, were prepared from these two SI copolymers. It was found that the morphology can be controlled by adjusting . For the blends with 0.57 ≤ ≤ 0.60, the morphological transition from lamellae to gyroid phases was observed upon increasing the temperature. We present an experimentally determined phase diagram for the blend by plotting χZ vs , where χ is the interaction parameter and Z is the reduced value of the total degree of polymerization of the block copolymer.
The kinetics of morphological transition from cylinders to lamellae was studied using a time-resolved small-angle x-ray scattering (SAXS) technique with synchrotron radiations. The sample examined is a polystyrene–block-polybutadiene–block-polystyrene (SBS) triblock copolymer having a number average molecular weight, Mn=6.31×104 and a volume fraction of polystyrene (PS) blocks, φPS=0.53. We previously reported that this sample formed a nonequilibrium morphology of polybutadiene (PB) cylinders when cast from its methyl ethyl ketone (MEK) solution. MEK is a selective solvent, i.e., good for PS chains but poor for PB chains. The transmission electron microscopy revealed that the PB cylinders transformed into wavy lamellae through coalescence when the samples were annealed at temperatures above the glass transition temperature of PS. It was also revealed that well-ordered lamellae were formed in the fully annealed samples. In order to discuss quantitatively the morphological transition and the subsequent lamellar ordering, we conducted the time-resolved SAXS measurements. Diffraction peaks arising from hexagonally packed cylinders were decreasing while those arising from alternating lamellae were increasing with time. It was found that the temporal change of the integrated intensity of the diffraction peak could not be fitted by a single exponential decay, but could be expressed by an exponential decay of time with β power. The values of β were in the range of 1<β<2. From the resultant decay time, apparent activation energies were further evaluated for coalescing cylinders and for ordering lamellae. These values were approximately in accord with each other, and it can be simply concluded that the kinetics of the morphological transition is governed by the polystyrene matrix phase.
New flexible fibrous glass-reinforced plastic (FRP) substrates for flat panel displays were developed. Optimizing the composition of the FRP by adjusting the difference in refractive index between a matrix resin and a glass fiber enabled the coexistence of a high transparency and a low coefficient of thermal expansion (CTE). An excellent smooth surface morphology was confirmed by the formulation of a coating resin. The stability of moisture impermeability depended on the surface smoothness and adhesion between a barrier layer and the coating layer. The moisture permeation rates of barrier substrates were below detection limits (<0:01 g m À2 day À1 ) on standard measurement equipment.
We report an experimental result of the thermally induced morphological transition from lamellar to gyroid phase in a binary blend of polystyrene-block-polyisoprene (SI) diblock copolymers. Two SI copolymers employed in this study have almost the same molecular weights but different volume fractions of polystyrene (PS) block (φPS=0.26 and 0.65). The blend was prepared by these two SI diblock copolymers and the overall volume fraction of PS block in the blend, φPS¯, was 0.58. Time-resolved small-angle x-ray scattering (SAXS) experiments were conducted to reveal morphological structures as a function of temperature from 120 to 205 °C during the heating with a rate of 2 °C/min. It was observed from SAXS results that the lamellar phase (L) was found below 164 °C, the gyroid phase (G) above 188 °C, and the coexistence of L and G phases between these temperatures. The gyroid phase was confirmed by transmission electron micrograph. The transition from L to G phase is different from a thermally induced transition of kinetically locked morphology formed by the vitrification of the PS matrix, because it was also found by a separate SAXS experiment for the specimen annealed for long times in which the lamellar phase was stable up to 140 °C, which is well above the glass transition temperature of the PS block. A temperature sweep of SAXS experiment with a smaller heating rate was a useful method to roughly estimate the transition temperature. Moreover, it was found from this experiment that the position of the first-order peak does not change remarkably upon the transition. Although the thermoreversibility of the transition between L and G phases has not yet been confirmed, it does not necessarily mean that the lamellar morphology is not stable at lower temperatures.
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