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Keywords:

  • activation energy;
  • DSC;
  • gelation;
  • isoconversional analysis;
  • polyurethanes;
  • viscosity buildup

Abstract

The complex cure kinetics of the reaction between oligomeric diphenylmethane diisocyanate (PMDI) and glycerol was characterized through thermal and rheological techniques. Isoconversional analysis of Differential scanning calorimetry (DSC) data resulted in the activation energy varying with conversion. Isothermal analysis gave activation energies ranging from 5 kJ/mol to 33.7 kJ/ mol, whereas nonisothermal data gave values for the activation energy ranging from 49.5 to 55 kJ/mol. Incomplete cure was evident in isothermal DSC, becoming diffusion controlled in the final stages of cure. DMA analysis on the cured material gave a glass transition temperature of 104 ± 3°C, which was evidence for vitrification of the curing system. The primary and secondary hydroxyl group reactivity was dependant on the isothermal cure temperature. Rheological studies of viscosity increase and tan δ changes with time revealed a complex cure process, with primary and secondary hydroxyl reactivity also showing dependence on isothermal cure temperatures, reflecting similar results obtained from isothermal DSC studies. The independence of tan δ on frequency was used to determine the point where the polymer formed an infinite network and was no longer able to flow, providing an overall activation energy attained at the gel point of 77.4 ± 4.4 kJ/mol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009