Softening of thermoplastic polyurethanes: a structure/property study

Softening of thermoplastic polyurethanes (TPU) in a simulated body environment (37 degrees C n-saline) was studied as a function of composition, structure and resultant morphology of these (AB)n type block copolymers. The structural variations were attempted by changing chemical composition and molecular weight of both hard A and soft B segments and their weight ratio in the polymer. In addition, the influence of bulk and/or surface modifiers, such as "reacted-in" polysiloxanes and fluorinated polyalkylether glycols, was also investigated. The degree of softening, expressed as a percentage decrease of the elastic modulus (5% tensile modulus) upon two hours exposure to the testing environment, is significant, reversible and depends on the ratio of hard to soft segment and the extent of microphase separation. Since these parameters can be selected during the polymer synthesis and processing into desirable shapes, the degree of softening can thus be controlled. This softening at body temperature represents one of the most notable performance advantages of these biomaterials.