Harnessing Catalysis Selectivity and Isophorone DiisocyanateAsymmetry for Tailored Polyurethane Prepolymers and Networks

We synthesized polyurethane (PU) materials via a typical two-stage industrial process based on the synthesis ofNCO-terminated prepolymers, followed by their crosslinking with polyols. We investigated the influence of metallic and organiccatalysts on (i) polyaddition kinetics between a challenging monomer (aliphatic and asymmetric isophorone diisocyanates, a.k.a.IPDI) and polyols and (ii) the structure and properties of corresponding PU prepolymers and networks. Tin (Sn)-free catalysts (Ti-and Zn-based) and even metal-free catalysts (guanidines, amidines, and amines) are competitive alternatives to a standard Sncatalyst. Besides the activity criterion, appropriately choosing the catalyst allowed us to adjust the prepolymer structure relying onrespective selectivities toward primary versus secondary isocyanate moieties as well as the propensity to favor functionalization overchain extension. By quantitative NMR spectroscopy, three different catalyst selectivities were pinpointed, which either favored theprimary or secondary isocyanate functions or promoted their isoreactivity. These selectivities were harnessed at both theprepolymerization and crosslinking stages to significantly decrease the reaction time by judicious and innovative combinations ofcatalysts with opposite selectivities toward primary/secondary isocyanates. We eventually evidenced the efficiency of thismethodology for tailored PU-based materials through in situ solid-state NMR monitoring of the crosslinking stage.

Automated summary

In this study, polyurethane (PU) materials were synthesized and the influence of metallic and organic catalysts on the kinetics, structure, and properties of the materials were investigated. The researchers found that tin (Sn)-free and even metal-free catalysts can be viable alternatives to the standard Sn catalyst, and the choice of catalyst can be used to adjust the structure and reaction time of the prepolymers.