TABLE OF CONTENTS Polyurethanes (PUs) composed of polyether or polyester soft segments and diisocyanate-based hard segments are well-known tough materials and are usually used as an additive to enhance the toughness of brittle materials as well as improve their thermal properties {894608}. Because of incompatibility between the hard segments and the soft segments, PUs undergo microphase separation resulting in hard-segment domains, soft-segment matrix and urethane-bonded interphase {831060}. The hard-segment domains act as physical crosslinks in the soft-segment matrix. The primary driving force for phase separation is the strong intermolecular interaction of the urethane units, which are capable of forming intermolecular hydrogen bonds [a.438]. Owing to such interactions, interconnected or isolated hard segments remain distributed in the soft-segment matrix, though the soft domain may contain some hard segments dissolved in it, which is evident from the hydrogen bonding of the urethane NH groups with the oxygen of the ether or ester linkages {760903}. These kinds of PU are utilised mainly as water dispersions (coatings, adhesives) and also as biomedical devices, temperature-sensing elements, polymer electrolytes, etc. Recent technological interest has been concerned with studies on composites containing conductive polymers and an inert polymer matrix.
The general PU decomposition mechanism is shown in Scheme 13 [a.122]. In general, there are three main pathways for the initial degradation of the urethane linkage, which are: dissociation to isocyanate and alcohol; dissociation to primary amine, olefin and carbon dioxide; as well as the formation of a secondary amine with elimination of carbon dioxide [a.1].
