Solid-state NMR spectroscopy was utilized to study the crystallinity and its correlation to the motional dynamics of a series of biphenol based poly(arylene ether sulfone) (PAES) copolymer analogues obtained by incorporating flexible aliphatic blocks. Introduction of a series of conformationally flexible aliphatic blocks into the rigid aromatic PAES blocks in the copolymer sequence had increased the crystallinity of the polymer matrix because the copolymer system with aliphatic blocks provided a decrease in the glass transition temperature (Tg) while maintaining a nonvariant melting temperature (Tm). Modified PAES copolymer systems with aliphatic blocks had yielded shorter (1)H T1 relaxation times and longer (1)H T1ρ relaxation times relative to the neat aromatic PAES copolymer. Trends observed in (1)H T1ρ and T1 data had demonstrated direct correlations to the observed ΔT (= Tm - Tg) and thus to the amount of crystallinity in the polymer matrix. Slow segmental reorientations of PAES blocks in a few milliseconds range also became slightly faster as the size of an aliphatic, segmented block became larger. Additionally, the local electronic environments of aromatic PAES blocks were invariant to the incorporation of aliphatic segments in the copolymer sequence.