The Synthesis of Low-Viscosity Organotin-Free Moisture-Curable Silane-Terminated Poly(Urethane-Urea)s

Abstract

This work explores the possibility of synthesizing moisture-curable silane-terminated poly(urethane-urea)s (SPURs) of low viscosity. First, NCO-terminated urethane prepolymers were prepared, followed by silane end-capping. The impact of polyol molecular weight and the ratio of isocyanate to polyol (NCO/OH) on viscosity and the properties of SPUR were examined. As alternatives to the organotin catalysts traditionally used for the polyurethane synthesis and curing processes, bismuth carboxylate catalysts were evaluated. In addition, the effect of organofunctional groups in the aminosilane structure (R1-NH-R2-Si(OR3) 3 ), i.e., R1 (alkyl, aryl or trimethoxysilyl-propyl), the spacer R2 (α or γ) and alkyl group R3 (methyl or ethyl), was examined. The chemical and physical structures of the SPUR were investigated by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR) and the mechanical properties were evaluated by tensile tests. The results reveal that silane-terminated, moisture-curable polyurethanes can be successfully synthesized and cured with bismuth carboxylate catalysts. SPUR exhibiting low viscosity, with adequate tensile strength and elongation can be prepared using environmentally benign bismuth carboxylate catalyst having a high metal content of 19%-21%, by utilizing secondary aminosilane end-cappers and an optimal combination of the polyol molecular weight and NCO/OH ratio.

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

“…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systems remain the strategy of choice efficiency-wise, because of health and environmental concerns, they have slowly been replaced by others catalysts to provide more sustainable alternatives.…”

“…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. 10,[13][14][15][18][19][20][21][22][23][24][25] In foams 12,22 and hybrid materials, [18][19][20][21][22][23][24][25] the impact of catalysts on structure, morphologies and consequently on material properties have already been partially investigated in order to design polyurethanes by either using a single catalyst or an combination of several catalysts. In the present work NCO-terminated prepolymers were synthetized in bulk with 4,4-methylenebis(phenylisocyanate) (4,4-MDI) and two poly(propylene glycol)s (PPG) (global functionality of polyol blend was equal to 2.45, characteristics are given in the experimental section) in the presence of different metallic and organic catalysts (Figures 1 and 2).…”

Microstructural evidence of the toughening mechanisms of polyurethane reinforced with halloysite nanotubes under high strain-rate tensile loading

“…Next, the partial silane termination occurred for an aminosilane content equivalent to weight fraction of 0.6% of the pre-polymer weight. As a result of the partial termination process, monodentate urea linkages and trimethoxysilane terminations were created in the PU’s prepolymer 50 . A small content of aminosilane was adopted to inhibit a substantial increase in the viscosity of the HNT/prepolymer solution.…”

Synthesis and Biological Activities of Organotin (IV) Carboxylates: A Review

“…26 For a high anti-fungal activity the total number of carbon atoms in the alkyl groups of a tri alkyltin compound should be about 9-12. 28 Organotin(IV) carboxylates have been used in silicone curing, 29 formation of polyurethane, 30 antifouling paints 31 and PVC stabilization. [32][33][34] Organotin(IV) carboxylates possess significant properties as antibacterial and antifungal agents and also as antitumor and anticancer drugs.…”