Poly(1,3-trimethylene carbonate), poly(TMC), has often been regarded as a rubbery polymer that cannot be applied in the biomedical field due to its poor dimensional stability, tackiness and inadequate mechanical properties. In this study we show that high molecular weight, amorphous poly(TMC) is very flexible, tough and has excellent ultimate mechanical properties. A number average molecular weight ð M n Þ of 100,000 was determined to be a critical value below which the polymer has negligible mechanical properties and poor dimensional stability. This corresponds to a molecular weight that is 40 times higher than the molecular weight between entanglements. The dependency of the mechanical properties levels off at M n values above 200,000. This very high molecular weight poly(TMC) shows good recovery after mechanical deformation, considering that the only resistance to chain flow is due to chain entanglement. Poly(TMC) cross-linked upon gamma-irradiation, resulting in the formation of an insoluble network. The degree of cross-linking increases with the radiation dose. The final mechanical properties of the high molecular weight poly(TMC) rubbers improve upon irradiation. Especially, the creep resistance increased, while the Young's modulus and tensile strength were not significantly affected. These biodegradable cross-linked rubbers may find wide application in soft tissue engineering where tough and elastomeric scaffolds are desirable.