Synthesis and structure-property relationships of biodegradable polyurethanes

Abstract

This chapter deals with a commercially very important part of the polyurethane (PU) polymer family, biodegradable polyurethanes (BioPUs). PUs are multiblock copolymers composed of a high molecular weight macrodiol, called a soft segment, and a hard segment composed of a diisocyanate and a low molecular weight diol. As a result of the thermodynamic incompatibility of the hard and soft segments in PU copolymers the phenomenon of microphase separation occurs. Nowadays, it is generally accepted that the overall properties, as well as the biocompatibility, of segmented PU and poly(urethane urea) (PUU) copolymers are correlated to the degree of microphase separation. The thermoplastic and elastic behaviour of these copolymers can be explained by their multiphase structure. The elastomeric properties of these copolymers are generally attributed to the phase separation of the hard and soft segments; the hard domains serve as crosslinks and reinforcing fillers in the matrix of the soft segment. It is generally assumed that the soft phase is responsible for the reversible elasticity of the polymeric material, whereas the hard phase is responsible for the mechanical strength properties.