Dynamics of Polyisoprene-Poly(p-tert-butylstyrene) Diblock Copolymer in Disordered State

Abstract

Linear viscoelastic and dielectric behavior was examined for a diblock copoly-mer composed of cis-polyisoprene (PI) and poly(p-tert-butylstyrene) (PtBS) blocks of the molecular weights MPI = 52.6 × 103 and MPtBS = 41.8 × 103 (PI weight fraction wPI = 55.7 wt %). These blocks were miscible and the copolymer was in the disordered state at temperatures examined, 20 ≤ T/°C ≤ 120. PI has the type-A dipole parallel along the chain backbone while PtBS does not. Thus, the dielectric response at low frequencies exclusively detected the global motion (end-to-end vector fluctuation) of the PI block, while the viscoelastic response reflected the motion of the copolymer chain as a whole. The dielectric data of the PI block exhibited prominent thermo-rheological complexity. Since the PI and PtBS blocks behaved as the fast and slow blocks at low T and this difference of their relaxation rates decreased at high T, the complexity was related partly to the dynamic frictional heterogeneity for the PI block resulting from th...