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This work investigates the two-step polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethylene oxide) macrodiols, and 1,4-butanediol (BD) as chain extender. At the end of the prepolymerization, the reaction mixture contains MDI in excess and a prepolymer with isocyanate end group. Then, BD and a solvent (tetrahydrofuran) were added to start the finishing stage under nominal stoichiometric equilibrium. The reaction was analyzed by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (1H-NMR), and size exclusion chromatography. 1H-NMR was employed to follow global concentrations of unreacted isocyanate end groups and internal urethane groups. This information enabled to estimate the following "effective" rate constants: k1 =1.07 x 10-3 L mol-1 s-1 for the prepolymerization; and k2=1.94 x 10-4 L mol-1 s-1 for the finishing stage. These values are subject to errors caused by biases introduced in the recipe, in the measurements, in the reaction conditions, in the quality of reagents, and in the reaction mechanism assumptions. Such errors also explain the dispersion of the published rate constants values. The ¹H-NMR measurements also enabled to estimate the evolution (with extent of reaction) of the numberaverage number of structural units along the prepolymerization and finishing stages; and such estimates reasonably verify Flory's classical expressions. [ABSTRACT FROM AUTHOR]

ABSTRACT Kinetics of curing of maleated castor oil glycerides with styrene was studied by differential scanning calorimetry and rheology. The resin was synthesized from biodiesel-derived crude glycerol. Curing rates were fitted to several empirical models (autocatalytic model, Kamal's model and a model with vitrification). The three models showed a good fitting with experimental data at conversions lower than 0.55 for temperatures ranging from 30 to 50°C. However, the model that includes vitrification showed a better fitting in the entire range of conversions and the same temperatures. At higher temperatures (50-60°C), some deviations were observed for the three models at low and high conversions. Gel times were obtained from rheological studies and the apparent activation energies were calculated thereof. Gel times were 300-2700 s. The values of apparent activation energy obtained for this castor oil-based copolymer (47.2-52.3 kJ/mol) were within range of commercial unsaturated polyester resins. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41344. [ABSTRACT FROM AUTHOR]