Dielectric normal mode relaxation of tethered polyisoprene chains in styrene-isoprene block copolymers

Abstract

Polyisoprene (PI) possesses type-A dipole moment aligned in the direction parallel to the chain contour and exhibits the dielectric normal mode relaxation due to the fluctuation of the end-to-end vector. Using this property of PI, we have studied the dynamics of the PI block chains of styrene-isoprene diblock copolymers (SI) and styrene-isoprene-styrene triblock copolymers (SIS). The results indicate that the distribution of relaxation times in SI having the lamella morphology is broadest and the distribution becomes narrow in order of cylinder and sphere morphologies. In SIS the dielectric normal modes are observed in the temperature range above the glass transition temperature of the styrene domain indicating that the styrene block chains can jump from one domain to the other.