Reactivity of common functional groups with urethanes: Models for reactive compatibilization of thermoplastic polyurethane blends

Two model urethane compounds, dibutyl 4,4′-methylenebis(phenyl carbamate) (BMB) and dioctyl 4,4′-methylenebis(phenyl carbamate) (OMO) were prepared by capping 4,4′-methylenebis(phenyl isocyanate) with n-butanol and n-octanol, respectively. The reactions of the two model urethane compounds with several small mono-functional compounds as well as two model poly(ethylene glycols) were carried out with neat mixtures at elevated temperatures. The ranking of reactivity of the functional groups with the urethanes was determined as follows-primary amine > secondary amine ≫ hydroxyl ∼ acid ∼ anhydride ≫ epoxide. Nuclear magnetic resonance spectroscopy (NMR) was used for the quantitative analysis. Fourier transform infrared spectroscopy was used to complement the NMR analysis. Conversions of carbamate in each reaction were monitored over time at constant temperature (200°C). The reactions between OMO and primary amine were conducted at 170, 180, 190, and 200°C and best described with a second-order bimolecular reaction model. The rate constant was estimated to be 1.8 × 10^-3 L · mol^-1 · s^-1 and activation energy 115 kJ · mol^-1.