Catalysis of Forward and Reverse Reactions of ϵ-Caprolactam-Blocked Polyisocyanate: Double Arrhenius Plots and Equilibrium Temperatures of a Thermally Reversible Reaction

Abstract

ϵ‐Caprolactam blocked‐polyisocyanate is a commercially valuable raw material used mainly in the single‐package polyurethane coatings. In this study, kinetics of forward (blocking) and the reverse (deblocking) reactions of ϵ‐caprolactam‐blocked polyisocyanate catalysed by DABCO ‐ a tertiary amine, bismuth neodecanoate, calcium(II) 2‐ethylhexanoate – both non‐tin organometallics and a tin catalyst were studied using a hot stage FT‐IR spectrophotometer. It was found that calcium(II) 2‐ethylhexanoate showed highest catalytic activity in the forward reaction whereas this catalyst showed lowest activity in the reverse reaction. DABCO and bismuth neodecanoate showed same catalytic activity and that activity was high compared to that of tin(II) 2‐ethylhexanoate in the forward reaction whereas only DABCO showed high activity in the reverse reaction. As these reactions were carried out adapting neat condition, the rate constants obtained were used to construct the double Arrhenius plots for this thermally reversible reaction. All the double Arrhenius plots showed intersection, from the intersection point, equilibrium temperature and equilibrium rate constants of these reactions were determined. Compared to uncatalysed reaction, DABCO reduced the deblocking temperature 25 °C and shifted the equilibrium temperature 6 °C. The data such as time required for 60% conversion into product, deblocking temperature and equilibrium temperature reported in this paper are vital in the manufacturing and in the application of ϵ‐caprolactam‐blocked polyisocyanate.

Polyurethane Coatings Based on Renewable White Dextrins and Isocyanate Trimers

“…It is a commercial isocyanate based on HDI in its trimer form and is primarily used as the hardener in two‐component polyurethane coatings with a NCO content of ≈22%. PUs from Desmodur N 3300 were produced with and without tin(II) 2‐ethylhexanoate as catalyst to investigate the catalytic effect . Additional experiments with modified carbohydrates (different D.S.)…”

A simple method to enhance the interface properties of carbon fibre/polyamide 6 composites: Grafted caprolactam-blocked 3-isocyanatopropyltriethoxysilane on carbon fibre surface

“…However, the -NCO is prone to failure in water, and thus IPTS cannot be hydrolyzed and cannot be condensed into polymer coating. In order to solve this problem, caprolactam (CPL) can be used as a blocking agent to block the -NCO, which renders the -NCO inactive at room temperature and able to withstand extended exposure to water without deterioration [39][40][41][42]. Furthermore, the CPL-blocked -NCO can undergo unblocking reaction and release -NCO again at high temperatures.…”

Scanning Electron Microscopy Investigation for Monitoring the Emulsion Deteriorative Process and Its Applications in Site-Directed Reaction with Paper Fabric

“…Hexamethylene diisocyanate (HDI) trimers emulsions fall into category of active emulsions since they should have free isocyanate (-NCO) contents in the emulsion to react with non-woven fabrics and paper [1][2][3]. Since this reaction could convert the hydrogen bonding into chemical bonds between fibers [4], paper can become a new high-strength, water-resistant, oil-resistant special paper after the treatment.…”