Using small-angle neutron scattering, the unperturbed chain dimensions of a series of poly(alkylene oxide)s (PAO's) were studied as a function of side-chain length. The PAO's were obtained using anionic ring-opening polymerization methods. The deuterated monomers were synthesized from commercially available precomponents. A systematic decrease of the chain dimensions with increasing length of the side chains was found. We also compare the PAO's with the chemically very similar poly(olefin)s with respect to the characteristic ratio C-infinity, the chain dimensions, and the packing length as a function of the molecular weight per backbone bond. In doing so, we found significant differences between the static properties of the two systems.