Linear segmented polyurethanes: I. A kinetics study

SPONT�N, MARISA E.; MEIRA, GREGORIO R.; JARAMILLO, FRANKLIN; POLO, MARA L.; ESTENOZ, DIANA A.

JOURNAL OF APPLIED POLYMER SCIENCE

JOHN WILEY & SONS INC

Lugar: New York; Año: 2018 vol. 135

0021-8995

This work investigates the 2-steps polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethylene oxide) (PTMO) 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 groups. Then, BD and a solvent (THF) were added to start the Finishing stage under nominal stoichiometric equilibrium. The reaction was analyzed by FTIR, 1H-NMR, and size exclusion chromatography (SEC). 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 = 1.07×10-3 Lmol-1s-1 for the Prepolymerization; and k2 = 1.94×10-4 Lmol-1s-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 explains the dispersion of the published rate constants values. The 1H-NMR measurements also enabled to estimate the evolution (with extent of reaction) of the number-average number of structural units along the Prepolymerization and Finishing stages; and such estimates reasonably verify Flory?s classical expressions.