Tin-free catalysts for the production of aliphatic thermoplastic polyurethanes

Abstract

Iron compounds, such as FeCl3, are highly active and temperature resistant catalysts for the solventless reaction of polyols with aliphatic diisocyanates to form thermoplastic polyurethanes.

Identifying competitive tin- or metal-free catalyst combinations to tailor polyurethane prepolymer and network properties

“…1,5 Nevertheless, even when aromatic isocyanates are employed, kinetic rates can be very low and reaching full conversion can prove challenging in an industrially viable reaction time. It is well-known that the catalyst choice influences kinetics [6][7][8][9][10][11][12][13][14][15][16][17] but only few studies deal with the systematic impact of said catalyst on polyurethane structures, molar masses, remaining free isocyanate and properties (viscosity, thermal, mechanical…). 10,[13][14][15][18][19][20][21][22][23][24][25] Mercury and tin catalysts have been widely used as catalysts in the fields of polyurethane synthesis and crosslinking due to their efficiency/selectivity towards the reaction between isocyanate and alcohol moieties.…”

“…Even though tin-based systems remain the strategy of choice efficiency-wise, because of health and environmental concerns, they have slowly been replaced by others catalysts to provide more sustainable alternatives. Researchers have made efforts in order to find alternative catalysts, either based on metals such as iron, 6,9,13,16 copper, 9,13 zinc, 6,10,16 bismuth, 6,10 titanium 6,10,16 and cobalt, 6,10 or strong organic bases such as 1,4diazabicyclo[2.2.2]octane (DABCO), 7,11,12,15,17 2,2'dimorpholinodiethylether (DMDEE), 7,11,14 various guanidines 15,17 and also organic acids. 17 Despite thorough investigations of catalysts' kinetics for polyurethane syntheses, few reports deal with the impact of catalysts on polyurethane properties such as molar masses, residual volatile isocyanate/corresponding amine or aniline, viscosities, mechanical and thermal properties of final materials, which are crucial parameters regarding regulations and processability of polymers.…”

Heterobimetallic complexes composed of bismuth and lithium carboxylates as polyurethane catalysts – alternatives to organotin compounds

“…4,15 However, owing to the toxicity of organotin compounds and the difficulties to remove them from the final products, 16,17 it has been a long-standing goal to develop more environmentally benign alternative catalysts. 18 In efforts to replace organotin catalysts, numerous Lewis-acidic metal complexes were identified as effective catalysts for the isocyanate-hydroxyl reaction, [19][20][21][22][23][24][25][26][27] including some inorganic tin complexes with amino/alkoxide ligands that exhibit thermolatent behaviour. [28][29][30][31][32][33][34][35] However, apart from DBTL, only a few metal complexes based on bismuth, aluminium, and zirconium are among the promising candidates for clear coat applications, as discoloration of the coating formulation is highly undesirable.…”

A robust super-tough biodegradable elastomer engineered by supramolecular ionic interactions

“…Therefore, a compromise must be found between biocompatibility and mechanical properties. In addition, for the preparation of aliphatic polyurethanes with high molecular weights, a toxic tin(II)based catalyst is commonly used which is not desirable for biological and biomedical applications [22,23].…”