Nanoscale heterogeneous structure of polyacrylonitrile-co-butadiene with different molecular mobilities analyzed by spin-spin relaxation time

To identify components with different spin-spin relaxation times, T ₂, in the solid-echo pulse proton nuclear magnetic resonance ( ¹H-NMR) spectra of crude acrylonitrile (AN)-butadiene rubbers (NBRs) with five different AN contents, we tried to understand the inhomogeneity in the crude NBRs in terms of their microstructures and molecular mobilities. The results of small-angle X-ray scattering, differential scanning calorimetry and dynamic mechanical analysis showed that crude NBRs have a single-phase and homogeneous morphology on the nanoscale. The microstructure of the crude NBRs shows alternately copolymerized AN-butadiene (BU) and BU block sequences, as indicated by ¹H-NMR spectra. The T₂ of the crude NBRs revealed three components with different molecular mobilities, even in homogeneous samples. The content of the highest-mobility component with T _2l is negligible. Judging from the AN content dependence of the ¹H ratio of these components, the low-mobility component with T _2s and high-mobility component with T_2m were assigned to the alternately copolymerized AN-BU sequences and BU block sequences, respectively.