RHEOLOGICAL BEHAVIOR OF HOMOGENEOUS POLY(ALPHA-METHYLSTYRENE)-BLOCK-POLYSTYRENE COPOLYMERS

A series of poly(alpha-methylstyrene)-block-polystyrene (P-alpha-MS-PS) copolymers having molecular weights ranging from 120 000 to 250 000 and different block length ratios were synthesized via anionic polymerization. Oscillatory shear flow properties of these block copolymers were measured using a Rheometrics mechanical spectrometer at temperatures ranging from 116 to 251-degrees-C, depending on the block copolymer composition. We have concluded that these block copolymers are homogeneous as determined by differential scanning calorimetry and, also, by logarithmic plots of dynamic storage modulus versus dynamic loss modulus. This conclusion is further supported by the fact that temperature-frequency superposition gives rise to temperature-independent master curves for the block copolymers. In view of the fact that the block copolymers synthesized must be regarded as entangled homogeneous block copolymers, using the concept of the tube model we have modified on an ad hoc basis the Stockmayer-Kennedy molecular viscoelasticity theory which was developed on the basis of the Rouse theory. The predicted zero-shear viscosities of the P-alpha-MS-PS diblock copolymers are compared with experimental results.