Hydroxyl telechelic natural rubber-based polyurethane: Influence of molecular weight on non-isothermal cure kinetics

• Natural rubber-based polyurethanes were synthesized.
• Influence of polyol molecular weight on cure kinetics was observed.
• A new efficient cure kinetic model based on mechanistic assumptions was proposed.

Isoconversional analysis was applied to non-isothermal bulk cure kinetics of uncatalyzed polyurethane (PU) resins based on telechelic hydoxyl natural rubber (HTNR) and poly[(phenyl isocyanate)-co-formaldehyde] (P-MDI). The dependency of apparent activation energy on conversion led to the identification of two different kinetic models, each involving two activation energies: a phenomenological model based on the Kamal–Sourour equation with non integer reaction exponents; and a new semi-mechanistic model assuming a main second order reaction between alcohols and isocyanates forming urethane linkages and a secondary reversible reaction forming allophanates that is known to become significant above 120 °C. Such a model based on mechanistic considerations allowed us to explain the variations of reactivity of the HTNR polyols with its average molecular weight.