Segmental mobilities in an athermal diblock copolymer melt far above T g by incoherent neutron scattering

Abstract

We report on incoherent elastic and quasielastic neutron scattering from a symmetric poly(isoprene-1,2 butadiene) (PIP-PVE) almost athermal diblock copolymer at different wave vectors Q in the range 0.18 to 1.8 Å−1. A fixed window temperature scan between 20 K and 300 K revealed the presence of segmental dynamics above 200 K and hence line shape analysis of the incoherent quasielastic spectra Sinc(Q,ω) was performed at high temperatures far above the single glass transition Tg(=221 K) to obtain the characteristic time scales. A two step nonexponential relaxation function was found adequate to describe consistently Sinc(Q,ω) with the faster relaxation time being comparable with the segmental relaxation time in bulk PIP at similar Q. This dynamic incompatibility may arise from dynamic heterogeneities as a consequence of composition fluctuations. The observation of a bimodal relaxation distribution function in PIP–PVE with low Tg contrast at temperatures far above the single Tg emphasizes the role of the intramolecular correlations due to chain connectivity.