The synthesis of a series of bis(ether anhydride)s with hindering substituents, especially t-butyl and methyl, has been developed using nucleophilic displacement reactions between nitrophthalodinitriles and substituted hydroquinones, bisphenols and a naphthalene diol. The bis(ether anhydride)s have been successfully incorporated into poly(ether imide)s with hindering residues by polymerization with diamines, with and without alkyl substituents. The thermal and mechanical properties of a number of the polymers and their permeabilities to several gases have been determined. The properties of the polymers are discussed, along with those of related polymers. It is shown that the properties are strongly controlled by their structural features. In particular, the flexibilities of polymer backbones and substituents are found to influence glass transition temperatures and, in conjunction with the influence of chain rigidity on packing, to influence gas permeabilities and permselectivities.