Cure and properties of unfoamed polyurethanes based on uretonimine modified methylene-diphenyl diisocyanate

✍ Scribed by Mayr, Anthony E; Cook, Wayne D; Edward, Graham H; Murray, Gerard J

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 185 KB
• Volume: 49
• Category: Article
• ISSN: 0959-8103
• DOI: 10.1002/(sici)1097-0126(200003)49:3<293::aid-pi367>3.0.co;2-y

✦ Synopsis

The curing behaviour of a series of polyurethanes based on modi®ed methylene±diphenyl diisocyanate (MDI) and poly(propylene oxide) polyols was studied using isothermal Fourier-transform infrared spectroscopy (FTIR), temperature-ramped differential scanning calorimetry (DSC) and adiabatic exotherm experiments. The effects of catalyst type and content, and of polyol molecular weight and functionality on the curing behaviour of the material were investigated. Increasing catalyst concentration or decreasing the polyol molecular weight raised the rate of reaction and shifted the DSC peak exotherm temperature to lower temperatures, but the heat of reaction was effectively constant. A marked increase in reaction rate was observed when a 1 °-alcohol-based polyol (from ethylene oxide end-capping) was used in place of the standard poly(propylene oxide) end-capped 2 °polyols. FTIR isocyanate conversion during polyurethane formation for a range of dibutyltin dilaurate (DBTDL) concentrations was satisfactorily ®tted to second-order kinetics. An approximately linear relationship between DBTDL catalyst concentration and reaction rate constant was found, but increasing the concentration of DBTDL was found to have no signi®cant effect on the magnitude of the activation energy. The activation energy for polymerization was found to be independent of the molecular weight of the diol or triol systems. Dynamic mechanical thermal analysis revealed a linear increase of the glass transition temperature with decreasing triol weight fraction, and was in good agreement with a theoretical model based on copolymer and crosslinking effects.