Investigation of various blocked isocyanates for debonding on demand

Abstract

Photocurable polymer networks based on mono- and multifunctional methacrylates represent the state-of-the-art technology for dental glues, which are used for temporary dental fixations such as braces, bridges, or crowns. Since those materials exhibit an excellent adhesion to the human tooth surface and moreover good mechanical properties, they are great alternatives to destructive techniques such as the conventional screws or bolts. Furthermore, these dental glues are rather inexpensive and display an esthetically pleasing tooth-like color, which makes them even more competitive towards conventional methods. One of the most important problems that are associated with these types of adhesive cements is their difficult removal after the temporary fixture is no longer needed. At this time, great force has to be applied to remove such restoratives, leading to a rather unpleasant, painful and long treatment for the patient. Therefore, a suitable glue that enables -debonding on demand- (DoD) would be very beneficial and simplify the job for the dentist. The target of this work was to investigate blocked isocyanates (BICs) towards their ability to deliver a suitable DoD concept for dental applications within the proposed temperature range of ~ 60-90 °C. Those thermally labile compounds cleave upon heating and form gas, which then leads to the expansion of the polymer network, thereby weakening the mechanical properties and enabling DoD. Therefore a set of 12 different active methylene compound- or phenol-based BICs was successfully synthesized and analyzed. The debonding temperature Td was determined via CO2 trapping using a Ba(OH)2 solution and the gas formation within a polymer matrix was analyzed using dynamic mechanical thermal analysis (DMTA) and simultaneous thermal analysis (STA). The gas formation within a polymer matrix and therefore the irreversible break up was successfully executed and BICs could be established as a promising concept for DoD.