Polyurethane-Bound Stabilisers

Addition of antioxidants and light stabilisers into the polyol component before its reaction with the isocyanate com ponent is common practice for polyurethane stabilisation. The stabilisers usually contain single OH and NH groups, which are involved in the mechanisms of stabilisation and the additives may then be regarded as monofunctional stabilisers. The OH and NH groups are very reactive towards the -N=C=O (isocyanate) groups so that a reaction between the stabiliser and the isocyanate groups during the synthesis of the polyurethane may occur to some extent. The stabiliser will become part of the polymer chain but the resulting structure will lose its active groups and consequently will not demonstrate the stabilisation effect. Some stabilisers have an additional OH group, not engaged in the stabilisation mechanisms. Having no constraints, these groups are more reactive towards the isocyanate groups. For these bifunctional stabilisers the resulting structure will bear the unreacted stabilising group, still effective, and a polyurethane-bound stabiliser will be obtained. The reaction of various commercial monofunctional and bifunctional stabilisers with isocyanates has been studied, as well as t heir use for the stahi lisation of polyurethanes, under conditions typical of practical applications. Whereas the reaction yields of the isocyanates with the monofunctional stahi lisers were very low (less than 15%). the reaction yields exceeded 90% for the hifunctional stahilisers. Therefore. commercial products with hi fu nctional structures may he regarded as reactive stabilisers, which yield polyurethan e-bound stabilisers.