Viscoelastic photoelastic behavior of copolymers of styrene and 2-methoxyethyl methacrylate. II. Blends of random copolymers

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Abstract
The viscoelastic photoelastic behavior of blends of random copolymers styrene/2-methoxyethyl methacrylate having the same mean content of styrene (27 wt %) was measured. Blends were prepared that differed in their chemical heterogeneity characterized by the variance of the chemical composition, between 10−6 and 10−1 (where Wi is the weight fraction of the i-th component in the blend and xi its chemical composition given by the weight fraction of styrene; x is the mean composition of the blend). It was found that the viscoelastic behavior in the main transition as well as in the rubberlike regions was very little affected by the chemical heterogeneity, if σw 2 ↬ 10−2; for example, the stress-optical coefficient in the rubberlike region increased with σw 2 by some 20%. For these samples the time-temperature superposition can be successfully used, and the time dependence of the superimposed curves does not practically depend on the heterogeneity of the blend. However, the sample with σw 2 ≅ 1−1 showed two-phase behavior; the temperature dependences of its photoelastic functions were in accord with the Takayanagi as well as with the isotropic model. The results obtained led to the conclusion that from the point of view of practical applications of viscoelastic behavior the blends of the copolymers studied can be considered homogeneous in the region of σw 2 ≤ 10−2.

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