Novel Furfural-Derived Polyaldimines as Latent Hardeners for Polyurethane Adhesives

Moisture-curing one-component polyurethane systems
in adhesive, sealant, and coating applications may show blister
formation upon cure. Blisters can be formed when carbon dioxide,
generated in the reaction with isocyanate and water, is trapped in
the film. This problem can be mitigated by employing latent
hardeners such as blocked polyamines, which are activated upon
moisture exposure. The hydrolysis of the latent hardener yields the
polyamine that quickly reacts with the isocyanate, forming urea
linkages, and then chain extends the polymer. The hydrolysis also
releases the blocking agent, which can potentially create an
unpleasant odor. In this work, a series of di- and trifunctional
aldimines were synthesized from commercially available polyamines, biobased hydroxymethyl furfural, and lauroyl chloride.
Hydroxymethyl furfural was first esterified with lauroyl chloride and subsequently condensed with the polyamines to form the
aldimines. The application of these novel aldimines in a model moisture-curing system allowed the preparation of blister- and odorfree
castings. Based on our results, the mechanical performance of the different aldimines in casting and adhesive applications could
be related to the polymer network density. This was dependent on the rate of the aldimine hydrolysis reaction to produce the
polyamine. In particular, the use of aldimines prepared from polyether amines and 1,5-diamino-2-methylpentane showed excellent
adhesive properties.