Polymers having mechanical properties approaching or exceeding commercial elastomers and engineering thermoplastics, but improved biostability, are described herein. In one embodiment, the polymers have a hard segment containing one or more disulfoxide or disulfone moieties and a soft segment connected to the hard segment to form an elastomeric polymer. The polymer is resistant to oxidation and/or hydrolytic degradation, particularly in vivo, which allows for the use of these materials in implants/devices which are implanted for an extended period of time. The ratio or percentage by weight of soft segment to hard segment can be varied based on the physical and mechanical properties of the desired device.