An o-nitrobenzyl-protected precursor was used as a phototrigger for the release of the diamine cadaverine in polyurethane adhesives based on castor oil as a renewable source of polyol and organic diisocyanates. This resulted in formulations with suitably controlled curing by photoactivation. This material shows faster curing when UV light is applied as compared to curing in the absence of irradiation, which was in situ monitored by rheological measurements. In addition, the adhesion performance is superior, reaching lap shear strength values of up to 4600 kPa, which is unprecedented for bio-based adhesives. On one hand, the in-depth chemical characterization with FTIR spectroscopy revealed that the slow release of cadaverine yields a well-balanced urethane/urea composition with direct impact on adhesion properties. The photocured bioadhesive was shown to bond a variety of surfaces, such as polyethylene or even wood. On the other hand, the direct one-time addition of cadaverine yields a material with approximately the same viscoelastic properties, which were achieved almost immediately as a consequence of the favored fast formation of urea bonds in detriment of urethanes, however, lacking adhesion properties.

A detailed experimental and theoretical study corroborates that the reductive deoxygenation of activated (allylic or benzylic) alcohols with excess Ti(III) proceeds via an allyl(benzyl)-radical and allyl(benzyl)-Ti, which is protonated, regioselectively in the case of allylic derivatives. The H atom of the newly formed C–H bond in the product originates from the –OH group of the starting material. The deoxygenation of lithium alkoxides or alcohols by using 1.0 mol of Ti(III) leads to the corresponding dimerization products in good yields. An excellent agreement with the experimental data was obtained by using a reaction kinetics simulator to discriminate between competing reactions.