The influences of selected catalysts on the structures and properties of polyurethane prepolymers and networks are investigated to adjust the catalyst/structure/properties relationship to a targeted application. This study highlights the...

We synthesized polyurethane materials via a typical industrial two-stage process based on the synthesis of NCO-terminated prepolymers followed by their crosslinking with polyols. We investigated the influence of metallic and organic catalysts on i) polyaddition kinetics between a challenging monomer (the aliphatic and asymmetric isophorone diisocyanate a.k.a. IPDI) and polyols, and on ii) the structure and properties of corresponding polyurethane prepolymers and networks. Tin-free catalysts (Ti, Zn-based) and even metal-free catalysts (guanidines, amidines, amines) are competitive alternatives to a standard tin catalyst. Beside the activity criterion, appropriately choosing the catalyst allows to adjust the prepolymer structure relying on respective selectivities toward primary vs. secondary isocyanate moieties, as well as propensity to favor functionalization over chain extension. By quantitative NMR spectroscopy, three different catalyst selectivities are pinpointed, which either favor the primary or the secondary isocyanate functions or promote their isoreactivity. These selectivities are harnessed both at the prepolymerization and crosslinking stages to significantly decrease reaction time by judicious and innovative combinations of catalysts with opposite selectivities toward primary/secondary isocyanates. We eventually evidenced the efficiency of this methodology for tailored polyurethane-based materials through in-situ solid-state NMR monitoring of the crosslinking stage.