This work compares the catalytic activity of several metal ions with a well-known catalyst, dibutyltin dilaurate (DBTDL), in the formation of poly(isocyanurate-urethane) (PIR-PUR) aerogels, and in turn, correlates the variable catalytic activity with the nanomorphology (SEM) and mechanical properties (Dynamic Mechanical Analysis – DMA) of the resulting aerogels. Fourth-period anhydrous salts from FeCl3 to GaCl3 as well as InCl3 and SnCl4 catalyze formation of PIR-PUR from 1,3,5-tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur N3300A) and triethylene glycol (TEG) at 20% w/w monomer concentration in acetonitrile. 119Sn NMR, indicates that the metal ion first complexes with TEG followed by reaction with the isocyanate. The gelation rate was followed with rheometry, and was found for fourth-period metal ions to increase from Fe to Cu, and decline from Cu to Ga. It was higher with Cu(II) or Cu(I). For equal catalyst concentrations, the fastest gelation (9 min) was observed with CuCl2 and the slowest with FeCl3 (5.75 h). As the catalyst concentration decreased, gelation time increased, and the morphology of PIR-PUR aerogels changed from bicontinuous to spheroidal. For equal gelation times, the morphology was about the same, irrespective of catalyst. A definitive trend was then observed between the elastic modulus (E) and the gelation time – thereby the morphology. The shape memory effect was also analyzed, and the fill factor varied from 0.49 – 0.62. The energy absorption capability was found inversely proportional to the gelation time and varied from 0.019 – 0.089 MJ/m3.

Morphology-dependent mechanical properties of shape memory poly(isocyanurate-urethane) (PIR-PUR) aerogels

ACS Spring Meeting 2021

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