A study was conducted to molecularly design very hydrophilic vinyl polymers. Various nonionic, water-soluble polymers with hydroxyl or primary amide groups in their side chains were prepared by radical polymerization of corresponding monomers or by polymer reactions to modify side chains derivatized in poly(vinyl ether)s. The functional groups interconnecting a hydrophobic main chain and a side chain included ether, secondary and tertiary amide, and ester groups. The number of hydroxyl groups incorporated in the side chains per monomer unit ranged from one to nine, and that of primary amide groups ranged from one to three. The spin-lattice relaxation times (T-1) of individual carbon atoms were measured in deuterium oxide (D2O) by an inversion-recovery Fourier transform method as an indicator of chain or group mobility. As for the effect of interconnecting groups on the mobilities of main and side chains, these increased in the following order : ether > ester and tertiary amide > secondary amide. Considerably reduced T-1 values were found with increasing number of hydroxyl groups in the side chains. The addition of lithium bromide to D2O solutions substantially increased T-1 values for hydroxyl group-derivatized polymers, indicating that intramolecular hydrogen bonds responsible for reduced T-1 values are broken to enhance chain or group mobility. On the other hand, minimal effect of lithium bromide addition was found for ether- or primary amide-derivatized polymers. These results suggest that, when an ether group is incorporated as an interconnecting group into a vinyl polymer and primary amide groups are well distributed at the terminal ends of the side chains, such a polymer could have high chain and group mobility, which may impart high hydrophilicity. The molecular structure-mobility relationship was discussed in terms of T-1 values. It is suggested that a combination of factors, such as the structure of interconnecting group, the structure of hydrophilic group, intra- and inter-pendant-group interactions, hydrogen bonding, and steric factors, all contribute to T-1 values.