This article proposes that, in binary blends of PEO with polymers bearing hydroxyl groups, only primary and not secondary hydroxyl groups form interchain hydrogen bonds with the skeletal ether oxygen of PEO. To prove this, PVA, propylated PVA, and two hydroxypropylated PVA derivatives-one with only secondary OH groups and the second with a mixture of primary and secondary OH groups, respectively-were used as one component which was blended with PEO in solution. The above hypothesis was confirmed for the resulting blend films using optical microscopic observations, SALS, WAXD, FTIR, and thermodynamic analyses with DSC. Curiously, this idea of selective hydrogen bonding between primary OH groups and oxygen in PEO may also be a driving force for the inclusion of PEO by alpha-cyclodextrin (CD) as a host-guest system since the primary OH groups at the C-6 position lie at the narrow end of the alpha-CD.