Alternative Polyurethanes Cured via Azide-Alkyne Cycloaddition Using Reduced-Viscosity Poly(alkynyl carbamate) Prepolymers

摘要

Conventional polyurethane coatings are crosslinked by reaction of a polyisocyanate prepolymer with a polyol. Recently there has been interest in the design of polyurethane polymers that can be crosslinked by alternative chemistries. The Storey Research Group at The University of Southern Mississippi has developed a series of these polymers for coatings, for which the final curing step involves azide-alkyne cycloaddition "click" chemistry. However, the conversion of a polyisocyanate prepolymer into a poly(alkynyl carbamate) results in dramatic viscosity increases due to hydrogen bonding of the carbamate structure, which is undesirable for coating application. To overcome this problem, a series of poly(alkynyl carbamate) prepolymers with lower viscosities was designed by chemically incorporating various glycol ether plasticizing moieties into the prepolymer chains. The glycol ether moieties were either of the conventional type, e.g. 2-ethoxyethanol, resulting in a non-load-bearing end group and a sacrifice of functionality, or they were specialty compounds containing both a hydroxyl group and an alkyne group, e.g. triethylene glycol monopropargyl ether, resulting in a load-bearing moiety and no sacrifice of functionality. This synthetic strategy, whether sacrificing the average functionality of the poly(alkynyl carbamate) or not, has proven to be effective in reducing the viscosity of the poly(alkynyl carbamate) prepolymer without compromising the final polyurethane coating performance.