A new type of copolymer is synthesized in a bulk polymerization from 1,3-dioxan-2-one and oxepan-2-one (epsilon-caprolactone) using either Sn-oct, ZnAc2, Bu(2)SnO, or Bu(3)SnCl as the catalyst. SEC analysis shows that it is possible to achieve high molecular weights and narrow molecular weight distributions. C-13-NMR analysis confirms the existence of copolymers. Conversion studies have been made and reactivity ratios, r(1) and r(2), have been determined to distinguish between the reactivities of 1,3-dioxan-2-one and oxepan-2-one. The Finemann-Ross method and the Kelen-Tudos method were used to calculate the ratios and the agreement was good between the methods. The composition of the copolymer agrees with the feed composition at high conversions. Thermal analysis of copolymers by DSC shows crystalline melting resulting from a somewhat blocky copolymer. The glass transition temperatures of the copolymers are in agreement with the Fox equation. The corresponding blends of the two homopolymers show a constant melting point and glass transition temperature. A nonionic insertion mechanism and a Lewis acid alcoholysis mechanism are discussed.