Phase separation of poly(2‐chlorostyrene)/poly(vinyl methyl ether) (P2CS/PVME) blends driven by a temperature gradient was investigated by phase‐contrast optical microscopy combined with digital image analysis. The samples were set in a temperature gradient in such a way that the two ends of the gradient cover both sides of the critical point. When the high‐temperature side of the gradient is increased with a constant rate, the interface that divides the miscible and the phase separated regions of the blend moves toward the low temperature side, leaving the phase separating region behind. It was found that in the vicinity of this interface, the phase separation takes place slowly via the spinodal decomposition process, giving interconnecting structures. In the region far from the newly growing interface, the droplet morphology appears as a result of the late stage of the spinodal decomposition. These droplets grow with time according to the power law ξ ∝ tβ, with β increasing from 0.30 to 0.44 along the temperature gradient. The phase separated blends with these graded morphologies show the broadened mechanical tanδ due to the graded structures distributed along the temperature gradient.

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