Oxygen transport characteristics, i.e., permeability, diffusivity, and solubility, have been determined for a variety of photopolymerized thiol-ene networks. Despite the abundance of thiol-ene research and the importance of such information, it is until now absent from the literature. One model network, which showed high oxygen barrier properties, was selected for further modification. Covalent bonding of functional groups to the network was enabled by an interesting approach: thio-Michael addition of various functionalized acrylates to a tetrathiol monomer. Cyano, hydroxyl, amide, and alkyl functional groups were explored. These new modified thiols were subsequently copolymerized with an isocyanurate-based multifunctional ene. This modification technique enabled a study on how different functional groups embedded in a uniform network affect T-g and oxygen barrier properties. All studied networks exhibited oxygen diffusivity and permeability which both spanned nearly 3 orders of magnitude. Correlation of both oxygen permeability and oxygen diffusivity with T-g was observed. This correlation allows the prediction of oxygen barrier properties of thiol-ene networks using T-g.