Poly(styrene)-supported N-heterocyclic carbene coordinated iron chloride as a catalyst for delayed polyurethane polymerization

Abstract

An advanced organometallic catalyst based on N-heterocyclic carbene (NHC) coordinated FeCl₃ has been synthesized and used to control the reaction rate in polyurethane (PUR) polymerization. The imidazolium (Im)-based NHC was functionalized on the surface of the supporting material of bead-type chloromethyl polystyrene (PS) resin. The PS-Im–FeCl₃ catalyst was synthesized through the coordination reaction between Im and FeCl₃. The successful formation, functional groups, structure, and geometry of the PS-Im–FeCl₃ catalysts were confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy techniques. A thin layer of Im was observed to be coated uniformly on the PS bead surface and FeCl₃ nanoparticles were observed to cover the coating layer homogeneously, as determined by field-emission scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy measurements. The PUR polymerization reaction was investigated through viscosity measurements and non-isothermal activation energy calculations by differential scanning calorimetry analysis. Based on the viscosity measurements, delayed PUR polymerization was achieved using the PS-Im–FeCl₃ catalyst system. The highest viscosity (6000 cP) was achieved without any catalyst, with triphenylene bismuth, and with the PS-Im–FeCl₃ catalyst after 23, 5, and 25 h of reaction time, respectively. Furthermore, the calculated activation energies (E_a) were 27.92 and 36.35 kJ mol⁻¹ for the no-catalyst and the PS-Im–FeCl₃ systems, respectively. Thus, the viscosity measurements and DSC analyses confirm that the PS-Im–FeCl₃ catalyst considerably increases the PUR reaction time. The Im–FeCl₃ catalyst supported by CMPS can control the reaction rate in PUR synthesis because of its high activity. Thus, the PS-Im–FeCl₃ catalyst can be used as a curing retardant in the PUR industry.