Aliphatic isocyanurates and polyisocyanurate networks

Abstract

The production, processing, and application of aliphatic isocyanate (NCO)-based thermosets such as polyurethane coatings and adhesives are generally limited by the surprisingly high viscosity of tri-functionality and higherfunctionality isocyanurates. These compounds are essential crosslinking additives for network formation. However, the mechanism by which these high viscosities are caused is not yet understood. In this work, model aliphatic isocyanurates were synthesized and isolated in high purity (>99%), and their viscosities were accurately determined. It was shown that the presence of the NCO group has a strong influence on the viscosity of the system. From density functional theory calculations, a novel and significant bimolecular binding potential of À8.7 kJ/mol was identified between NCO groups and isocyanurate rings, confirming the important role of the NCO group. This NCO-to-ring interaction was proposed to be the root cause for the high viscosities observed for NCO-functional isocyanurate systems. Molecular dynamics simulations carried out to further confirm this influence also suggest that the NCO-toring interaction causes a significant additional contribution to viscosity. Finally, model functional isocyanurates were further reacted into densely crosslinked polyisocyanurate networks which showed interesting material properties.

The Trimerization of Isocyanate‐Functionalized Prepolymers: An Effective Method for Synthesizing Well‐Defined Polymer Networks

“…Therefore, this reaction can only be carried out to low conversion. After removal of the unreacted monomer fraction, the resulting polyisocyanate mixture consists of a distribution of trimers and higher‐order oligomers, with a corresponding distribution in functionality that is on average larger than 3 . To form the poly(urethane–isocyanurate) network, this polyisocyanate mixture is reacted with a polymeric diol as a 2‐component system.…”

Polyurethanes for coatings and adhesives – chemistry and applications

“…As the trimer (oligomer n = 3) itself is reactive again it forms structures with n = 5, n = 7, … and the reaction is controlled by using an excess of monomer, which needs to be removed after the reaction by stringent distillation. The ratio of trimer to oligomers with n = 3, n = 5, n = 7, … is used to adjust the molecular weight, functionality and viscosity of polyisocyanates . Trimers are chemically and thermally very stable; they are often based on HDI, IPDI or TDI.…”

“…The ratio of trimer to oligomers with n = 3, n = 5, n = 7, … is used to adjust the molecular weight, functionality and viscosity of polyisocyanates. 27 Trimers are chemically and thermally very stable; they are often based on HDI, IPDI or TDI.…”

Investigation on the intermolecular interactions in aliphatic isocyanurate liquids: revealing the importance of dispersion

“…In a previous work [24], the viscosity of various aliphatic isocyanurate liquids, both functional and non-functional(i.e. without any free NCO groups) was measured.…”

“…It was shown that the viscosity of functional isocyanurates is at least three orders of magnitude larger than that of their diisocyanate precursors (e.g. 614 mPa • s for HDI trimer [24] compared to 2.3 mPa • s for HDI [25]) and increasing as the alkylene chain-length between the isocyanate and isocyanurate decreases. Conversely, a weak dependence on alkylene chain length was found in the case of non-functional molecules, and smaller viscosities (200 mPa • s) were found.…”