Rheo-Optical And Dielectric Study On Dynamics Of Bottlebrush-Like Polymacromonomer Consisting Of A Polyisoprene Main Chain And Polystyrene Side Chains

For bottlebrush-type polystyrene polymacromonomer consisting of a polyisoprene main chain and polystyrene side chains (PI-PS-bPM), dynamic birefringence and viscoelasticity measurements were conducted over a wide range of frequencies covering from the glass-to-rubber transition zone to the flow zone. In addition, dynamic dielectric measurements were conducted at low frequencies to selectively detect the end-to-end motion of the main chain (PI) having type-A dipoles. The complex modulus and complex strain-optical coefficient were decomposed into contributions from the main chain and branch on the basis of the modified stress-optical rule, MSOR The terminal relaxation of the complex modulus and dielectric loss commonly reflected the end-to-end motion of the main chain PI, and their relaxation times, tau(G) and tau(epsilon), obeyed an empirical relationship established for monodisperse linear type-A chains, tau(epsilon) congruent to 2 tau(G). The dielectric relaxation intensity of the PI main chain, Delta epsilon(M), was found to be approximately 5 times larger than that expected for linear PI equivalent to this main chain (Delta epsilon(M) = 4.20 phi(main)Delta epsilon(PI) with phi(main) being the main chain volume fraction), which suggests that the mean-square end-to-end distance of the main chain is about 5 times larger than that of linear PI, and thus, the main chain is more rigid than linear PI. This result was consistent with an increase in dynamic rigidity of the main chain (compared to PI) deduced from the rheo-optical analysis. Furthermore, the main chain rigidity of PI-PS-bPM was found to be about a half of a previously examined polymacromonomer, PSPS-bPM, having PS in both branch and backbone. This difference between PI-PS-bPM and PS-PS-bPM was attributed to the branch density per unit length of the main chain that was lower for PI-PS-bPM.