Reduction of Birefringence by Dynamic Asymmetry in Miscible Blends of Dissimilar Polycarbonates

Abstract We found that the birefringence of miscible blends of dissimilar polycarbonates was lower than those of the neat component polymers though the sign of the birefringence was same. The modulus and birefringence of the blends decreased more gently in the glass transition region but more steeply in the rubbery plateau region than those of the neat component polymers. The modulus and birefringence relaxation curve fitting with the KWW and modified Rouse equations revealed wider distortion relaxation and orientation distributions in the blends than in the neat component polymers. The wide distortion relaxation might be attributed to the dynamic asymmetry of the blends. The orientation relaxed faster in the blend than in the component polymers, indicating accelerated orientation relaxation, which could be explained by assuming cooperative relaxation of the component polymers strongly affected by fast relaxation component of the low-Tg one due to the dynamic asymmetry with a large glass transition temperature difference between the component polymers. Owing to the accelerated relaxation, the elongated blends exhibited lower birefringence than the component polymers.