Adhesive behavior of polyurethane-based materials

The role of prepolymer on the interfacial strength of polyurethane-based as semblies is examined for two hydroxyl-terminated (telechelic) polybutadiene s, R45M and R45HT. Although it is known that both prepolymers lead to very different adhesive behavior, the reasons that explain this are not understo od. In this study, we show that two main effects have to be considered: the length of the free chains, which can diffuse across the interface during t he formation of the joint and the relative reactivity of the various hydrox yl groups of the chains and chain extenders with the isocyanate. The R45M c hains are more efficient connectors than the R45HT chains. Migration of cha in extenders and isocyanate over large distances creates a thick interphase where physical crosslinks appear. This interphase is thicker for R4BM-base d polyurethane showing the role of the chain reactivity. (C) 2000 John Wile y & Sons, Inc. J Appl Polym Sci 76: 665-671, 2000.