wider than the Rouse segment size for linear polystyrene. Dynamic birefringence and dynamic viscoelastic measurements around glass transition zone showed that the complex Young's modulus and the strain optical coefficient of the copolymer was very similar to those of linear polystyrene. The complex Young's modulus was separated into the rubbery and the glassy component moduli with the aid of the modified stress optical rule. The stress optical coefficients for the glassy and the rubbery

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... ts, respectively, agreed with those for linear polystyrene, meaning that no indication of microphase separation was rheologically detected over a whole range of frequencies studied. The effect of branching was not observed in the frequency dependence of the glassy component. The Rouse segment size calculated from the limiting modulus of the rubbery component at high frequencies was not affected by branching. Dynamic viscoelastic measurements around the terminal flow zone revealed that two relaxation modes were involved in the rubbery zone. The mode observed at short times was attributed to motion of polystyrene branches, and the other mode at long times was related to the motion of poly (2-vinylpyridine) trunk. Although Mw of poly (2vinylpyridine) was much higher than the molecular weight of entanglement strands of linear polystyrene, the rubbery plateau zone was not clearly observed, possibly due to the dilution of entanglements by branching