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Linear segmented polyurethanes: I. A kinetics study
Author(s) -
Polo Mara L.,
Spontón Marisa E.,
Jaramillo Franklin,
Estenoz Diana A.,
Meira Gregorio R.
Publication year - 2018
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.45747
Subject(s) - prepolymer , isocyanate , polymer chemistry , polymerization , fourier transform infrared spectroscopy , solvent , tetrahydrofuran , reaction rate constant , materials science , methylene , kinetics , chemistry , polyurethane , chemical engineering , organic chemistry , composite material , polymer , engineering , physics , quantum mechanics
ABSTRACT 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 ( 1 H‐NMR), and size exclusion chromatography. 1 H‐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: k 1 = 1.07 × 10 −3 L mol −1 s −1 for the prepolymerization; and k 2 = 1.94 × 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 1 H‐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. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135 , 45747.