Novel stabilisers acting simultaneously as molecular-weight regulators in soluble elastomeric polyurethanes

Three new low-molecular-weight stabilisers, bearing in their molecules a tri(dimethylsiloxane) chain, end-capped with primary OH groups, have been synthesised and characterised. One is based on a sterically hindered phenolic antioxidant, the others on sterically hindered piperidines (HALS-type). When added to the reaction mixture for the preparation of model soluble elastomeric polyurethanes (containing a polybutadiene α,ω-diol, a diisocyanate and a catalyst), each of these stabilisers, due to the presence of the OH group, is joined by a covalent bond at one or both chain ends of the polyurethane formed, and acts simultaneously as a molecular-weight regulator. Thermoanalytical methods revealed that the stabilising efficiency of these polymer-bound structures is comparable with that of their low-molecular-weight analogues, physically admixed with the polyurethane. The advantage of these chemically fixed stabilisers lies in the fact that they remain in the matrix and cannot be evaporated nor washed out.