One-step sealant based on electronegatively substituted phenolic blocking agents and aliphatic isocyanates providing fast cures and improved stability

One-step sealant compositions are provided which have a moisture-activated curative component and an aliphatic isocyanate-terminated polyol component blocked with a phenol substituted with an electron-withdrawing group having a Hammett sigma p constant in the range from >0.24 to about 0.73. In this range, the blocking phenol is rapidly displaced by an amine group so that the sealant cures in less than one-half the time required for an analogous sealant in which end-capping is performed with an aromatic polyisocyanate. Yet the novel sealant is also stable for more than twice as long, in excess of nine months, when sealed under nitrogen in a container and stored at 25 DEG C. and 50% relative humidity. Sealants of this invention thus provide both, a desirable fast cure rate of less than 8 hr to cures to a viscosity of 100,000 cp in a 50% relative humidity atmosphere at 25 DEG C., and exceptional stability when stored. Such sealants are particularly desirable because the improvement in rate of cure and in shelf life is relatively insensitive to the specific aliphatic polyisocyanate or the polyester or polyether polyol used.