Birefringence and Viscoelasticity of Graft Copolymer
Kenji MATSUNO, Tadashi INOUE and Hiroshi WATANABE
Abstract:A graft copolymer having poly (2-vinylpyridine) trunk (Mw = 1.87~105) and sixty-eight polystyrene branches (Mw = 4.98~103) was synthesized by anionic coupling method. The trunk span between branching points was about two times wider than the Rouse segment size for linear polystyrene. Dynamic birefringence and dynamic viscoelastic measurements around glass transition zone showed that the complex Youngfs modulus and the strain optical coefficient of the copolymer was very similar to those of linear polystyrene. The complex Youngfs 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 components, 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 (2-vinylpyridine) 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. Key Words:Graft copolymer, Birefringence, Viscoelasticity, Modified stress optical rule, Rouse segment