Billion-fold rate enhancement of urethane polymerization via the photothermal effect of plasmonic gold nanoparticles

Abstract

We use the photothermal effect of gold nanoparticles (AuNPs) to provide billion-fold enhancement of on-demand bulk-scale curing of polyurethane. We follow the course of this polymerization using infrared spectroscopy, where we can observe the loss of both isocyanate and alcohol stretches, and the rise of the urethane modes. Application of 12.5 MW cm⁻² of 532 nm light to a solution of isocyanate and alcohol with 0.08% w/v of 2 nm AuNPs results in the billion-fold enhancement of the rate of curing. This result is intriguing, as it demonstrates the ability of nanoscale heat to drive bulk transformations. In addition, the reaction is strongly exothermic and results in a relatively weak bond, both of which would preclude the use of bulk-scale heat, highlighting the unique utility of the photothermal effect for driving thermal reactions.