DIELECTRIC NORMAL-MODE RELAXATION OF TETHERED POLYISOPRENE CHAINS IN STYRENE-ISOPRENE BLOCK-COPOLYMERS

Polyisoprene (PI) possesses type-A dipole moment aligned in the direct ion parallel to the chain contour and exhibits the dielectric normal m ode 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 chai ns of styrene-isoprene diblock copolymers (SI) and styrene-isoprene-st yrene triblock copolymers (SIS). The results indicate that the distrib ution of relaxation times in SI having the lamella morphology is broad est and the distribution becomes narrow in order of cylinder and spher e morphologies. In SIS the dielectric normal modes are observed in the temperature range above the glass transition temperature of the styre ne domain indicating that the styrene block chains can jump from one d omain to the other.