INV SUPERIOR JUBILADO
MEIRA Gregorio Raul
artículos
Título:
Linear segmented polyurethanes: I. A kinetics study
Autor/es:
POLO, MARA L.; SPONT�N, MARISA E.; JARAMILLO, FRANKLIN; ESTENOZ, DIANA A.; MEIRA, GREGORIO R.
Revista:
JOURNAL OF APPLIED POLYMER SCIENCE
Editorial:
JOHN WILEY & SONS INC
Referencias:
Lugar: New York; Año: 2018 vol. 135
ISSN:
0021-8995
Resumen:
This work investigates the two-step polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethyleneoxide) macrodiols, and 1,4-butanediol (BD) as chain extender. At the end of the prepolymerization, the reaction mixturecontains MDI in excess and a prepolymer with isocyanate end group. Then, BD and a solvent (tetrahydrofuran) were added tostart 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 globalconcentrations of unreacted isocyanate end groups and internal urethane groups. This information enabled to estimate the following?effective? rate constants: k151.07 3 1023 L mol21 s21 for the prepolymerization; and k251.94 3 1024 L mol21 s21 for the finishingstage. 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 publishedrate constants values. The 1H-NMR measurements also enabled to estimate the evolution (with extent of reaction) of the number averagenumber of structural units along the prepolymerization and finishing stages; and such estimates reasonably verify Flory?s classicalexpressions.