Flame‐retardant, phosphorous‐based polyurethane triazoles via solvent‐free and catalyst‐free azide–alkyne cycloaddition and their cure kinetics

Abstract

A novel class of phosphorous‐containing polyurethane triazoles (PUTs) with self‐extinguishing property is reported. Initially, a set of new urethane diazide monomers were synthesized by reacting diisocyanates (DI) (isophorone (IPDI), hexamethylene (HDI), and toluene (TDI)) with 2‐azidoethanol and characterized by FTIR, 1H NMR, 13C NMR, and ESI‐MS analysis. Later, the corresponding PUTs were synthesized via azide–alkyne cycloaddition of urethane diazides with triprop‐2‐ynyl phosphate under solvent‐free and catalyst‐free conditions at 80°C via thermal polymerization. Cure kinetic study of the thermally induced polymerization of PUTs was performed to correlate with isocyanate functionality. The activation energies (Ea) of the PUTs derived from nonisothermal multiheating rate DSC tests were fitted to Borchardt–Daniels model. The Ea's were found to be proportional to heating rates for all PUTs and confirmed optimum percentage conversion at lower heating rates. The experimental findings were found to corroborate well with Borchardt–Daniels model. The PUTs were characterized by FTIR, TGA, DSC, MCC, LOI, lab‐scale flame tests, and EDX analysis. All PUTs were self‐extinguishable, but TD‐PUT with aromatic functionality (TDI‐based) demonstrated superior extinguishing performance with lowest total heat release (6.11 kJ/g), peak heat release rate (42.04 W/g), heat release capacity (85.59 J/g K), and 31% LOI comparatively. Lab‐scale flame tests on PUTs confirmed their self‐extinguishing property with little or no smoke evolution. Such PUT resins can be blended with conventional polyurethane coatings for fire‐retardant applications.

1,2,3‐Triazole rich polymers for flame retardant application: A review

“…For instance, PUTs such as IPD-PUT (bulk polymerization of N3-IPD and triprop-2ynyl phosphate), HD-PUT (bulk polymerization of N3-HD and triprop-2ynyl phosphate), and TD-PUT with$20 wt% of nitrogen content for pure samples have shown lesser nitrogen content of 6-8 wt% for post-burn samples. 77 This corroborates the expulsion of nitrogen gas from triazole moiety during the combustion cycle. EDX-elemental analyses of the PUTs before and after burning are exemplified in Figure 5.…”

“…Whereas, after the expulsion of nitrogen gas from triazole moiety, the post‐burn sample comparatively contains lesser nitrogen atoms. For instance, PUTs such as IPD‐PUT (bulk polymerization of N3‐IPD and triprop‐2ynyl phosphate), HD‐PUT (bulk polymerization of N3‐HD and triprop‐2ynyl phosphate), and TD‐PUT with~20 wt% of nitrogen content for pure samples have shown lesser nitrogen content of 6–8 wt% for post‐burn samples 77 . This corroborates the expulsion of nitrogen gas from triazole moiety during the combustion cycle.…”

“…We extended our work on triazole rich phosphorusbased self-extinguishable PU coatings by making polyurethane triazoles (PUTs) through the bulk polymerization (solvent-free and catalyst-free) of different urethane 77 Here, we have used azide-alkyne click chemistry not only for making triazole into PU backbone but also used as a tool for constructing novel PUTs. It was found that all the PUTs were immediately self-extinguished with the intumescent char after removal of ignition (ignited for 10 s with a propane torch) in the lab-scale flame test.…”

“…From the available data, the LOI values of triazole-based FR polymers have attained noticeably impressive values ranging from 25% to 31%. 77 With limited literature available on 1,2,3-triazole-based FR systems the possibility to explore such non-halogenated FRs for a wide…”

“…We extended our work on triazole rich phosphorus‐based self‐extinguishable PU coatings by making polyurethane triazoles (PUTs) through the bulk polymerization (solvent‐free and catalyst‐free) of different urethane diazides (synthesized from 2‐azidoethanol and isophoronediisocyanate [N 3 ‐IPD], hexamethylenediisocyanate [N 3 ‐HD], and toluene diisocyanate [N 3 ‐TD]) with triprop‐2ynyl phosphate through azide‐alkyne click chemistry 77 . Here, we have used azide‐alkyne click chemistry not only for making triazole into PU backbone but also used as a tool for constructing novel PUTs.…”