Miscibility behaviors of poly[oxy(alkylsulfonylmethyl)ethylene]s, poly[oxy(alkylsulfonylmethyl)ethylene-co-oxyethylene]s, and poly[oxy-2,2-bis(alkylsulfonylmethyl)trimethylene]s were studied. A group contribution parameter for the aliphatic sulfone group was developed and used to calculate solubility parameters for both oxyethylene series. Though there is no specific interaction between these polymers, they have similar backbones and the same side chains, and many pairs were found to be miscible. The poly(oxytrimethylene)s were miscible with certain oxyethylene homo- and copolymers even when their solubility parameters were very different (Delta delta less than or equal to 1.5 (cal/cm(3))(1/2)). However, no polymer was miscible with another containing the same backbone even when their solubility parameters were very close. The miscibility range was used to determine solubility parameters for two members of the oxytrimethylene series and a group contribution parameter for the gem-disubstituted disulfone group. When the unoccupied volumes of two miscible polymers are very different, volume contraction and negative heat of mixing can be expected; this decreases the free energy of mixing and promotes the miscibility of polymers with relatively large solubility parameter differences. The permeability coefficient and the chemical structure of poly[oxy-2,2-bis(methylsulfonylmethyl)trimethylene] imply that its unoccupied volume (probably excluded volume due to poor packing of the bulky substituent) is larger than those of the other backbone polymers. Miscible blends of oxytrimethylene polymers with oxyethylene homo- or copolymers showed volume contraction upon mixing. This implies that the monosubstituted oxyethylene polymers can pack into the excluded volume of the 3,3-disubstituted oxytrimethylene polymers.