Harnessing Catalysis Selectivity and Isophorone Diisocyanate Asymmetry for Tailored Polyurethane Prepolymers and Networks

Abstract

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.

Triazabicyclodecene: A versatile catalyst for polymer synthesis

“…Certain investigations have revealed that in specific systems, MTBD or DBU tends to outperform TBD in terms of effectively catalyzing the addition of alcohols to isocyanates. 203,204…”

“…Within the realm of organocatalysts, it is important to note that TBD is not universally the optimal choice. Certain investigations have revealed that in specific systems, MTBD or DBU tends to outperform TBD in terms of effectively catalyzing the addition of alcohols to isocyanates 203,204 …”

Paving the Way towards Sustainability of Polyurethanes: Synthesis and Properties of Terpene-Based Diisocyanate

“…However, the isocyanate group on C 1 appears to be less hindered than that on C 8 , which could enhance its reactivity. Indeed, it has been shown that in most instances, the secondary isocyanate group in IPDI exhibits higher reactivity due to lower steric hindrance in the chair conformation when compared to the quaternary isocyanate group [40,41]. Nevertheless, some catalysts have proven to be effective for activating both isocyanates in a similar manner [41][42][43][44][45][46][47][48].…”

Injectable and photocurable macromonomers synthesized using a heterometallic magnesium–titanium metal–organic catalyst for elastomeric polymer networks

“…5,6 Tin-based catalysts are another class of popular and effective catalysts for the synthesis of polyurethanes. [7][8][9] One commonly used example is dibutyltin dilaurate (DBTDL), 10 which is also used for the synthesis of polyesters 11,12 and many other elastomers, especially for coating applications. 13 However, tin-based compounds are also toxic (with toxicity threshold of 3 ppm (ref.…”