Polyurethane-bound stabilisers

Addition of antioxidants and light stabilisers into the polyol component be fore its reaction with the isocyanate component is common practice for poly urethane stabilisation. The stabilisers usually contain single OH and NH gr oups, which are involved in the mechanisms of stabilisation and the additiv es 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 reactio n 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 group s and consequently will not demonstrate the stabilisation effect. Some stab ilisers have an additional OH group, not engaged in the stabilisation mecha nisms. Having no constraints, these groups are more reactive towards the is ocyanate groups. For these bifunctional stabilisers the resulting structure will bear the unreacted stabilising group, still effective, and a polyuret hane-bound stabiliser will be obtained. The reaction of various commercial monofunctional and bifunctional stabilisers with isocyanates has been studi ed, as well as their use for the stabilisation of polyurethanes, under cond itions typical of practical applications. Whereas the reaction yields of th e isocyanates with the monofunctional stabilisers were very low (less than 15%), the reaction yields exceeded 90% for the bifunctional stabilisers. Th erefore, commercial products with bifunctional structures may be regarded a s reactive stabilisers, which yield polyurethane-bound stabilisers.