We have been studying the blood compatibility of polymeric materials from the viewpoint of their water structure, and have proposed that freezable water interacting with polymer molecules plays an important role in determining that compatibility. As we found that water-soluble poly(acryloylmorpholine) interacted with water, resulting in the formation of 'bound water', we newly prepared water-non-soluble poly(acryloylmorpholine-r-butyl methacrylate) (denoted as ACMO co-polymer) with various composition ratios. In addition, the properties of a co-polymer based on N,N-diethylacrylamide (DEA co-polymer), where DEA has a similar chemical structure to ACMO, except that DEA has no ether oxygen, were compared with that of the ACMO co-polymer. Contact angle and DSC analysis revealed that an increase in the content of an N-substituted acrylamide unit in the co-polymers enhanced the hydrophilicity of the polymer and that the hydrophilicity of the ACMO co-polymer was stronger than that of the DEA co-polymer. As for the water structure, it was found that the ACMO co-polymer had a lot of bound water compared to the DEA co-polymer. The difference in these properties between the ACMO and DEA co-polymers was due to the ether oxygen of the morpholine group. At the same time, in vitro blood compatibility tests showed that the ACMO co-polymer exhibited a much better performance than the DEA co-polymer. The water structure and blood compatibility is discussed in detail.