Polyurethane coatings cured via azide-alkyne cycloaddition using reduced-viscosity poly(alkynyl carbamate) prepolymers

Abstract

Alternative crosslinking polyurethanes (ACPUs) were created by reacting a commercial allophanate-modified polyisocyanate with propargyl alcohol to yield a poly(alkynyl carbamate); a polyazide co-reactant was created from an acrylic polyol. Conversion of the polyisocyanate into the corresponding poly(propargyl carbamate) resulted in a dramatic viscosity increase. Poly(alkynyl carbamate) prepolymers with lower viscosities were designed by replacing various fractions of the propargyl alcohol with commercial glycol ether plasticizers, ethylene glycol monoethyl ether (EGMEE), diethylene glycol monomethyl ether (DEGMEE), and diethyleneglycol monobutyl ether (DEGBE). Triethylene glycol monopropargyl ether was also studied to provide plasticization with no sacrifice of alkyne functionality. For each commercial glycol ether plasticizer, viscosity was unaffected or increased at a loading level of 10 mol%. At 25 mol%, average viscosity reduction was 36 %, with DEGBE yielding the greatest reduction at 55 %. At 33 mol%, no further decreases were observed. Triethylene glycol monopropargyl ether yielded a 76 % reduction in viscosity at 33 mol%; 100 mol% substitution yielded no further reduction. Coatings produced from the modified poly(alkynyl carbamate)s were softer and displayed lower glass transition temperatures compared to a polyisocyanate/polyol control and a 100 % propargylated poly(alkynyl carbamate)/polyazide control. Solvent resistance of the modified coatings was the same as the controls except for those created from DEGBE and from DEGMEE at 33 mol%.