An ionomeric, modified poly(1,4-butylene terephthalate) copolymer comprising: polyester units comprising non-ionomeric ester units and ionomeric ester units substituted with an inorganic ionic group; and polyester units having at least one residue that is derived from a polyethylene terephthalate component selected from the group consisting of polyethylene terephthalate and polyethylene terephthalate copolymers is described.