Carboxylic polyurethane/organoclay nanocomposites and their properties

New nanocomposite films were prepared from a dispersion of organically modified montmorillonite as the filler and flexible polyurethane as the matrix. The polyurethanes containing a small amount of carboxylic groups were synthesized from 4,4'-diphenylmethane diisocyanate (MDI), 1,4-butanediol (1,4-BD), and poly(tetramethyleneoxide diol) (PTMO) of 1000 average molecular weight, the carboxylic unit being included by means of dimethylol propionic acid (DMPA) or tartaric acid (TA). For comparison, polyurethane without carboxylic moieties was also synthesized. The polymers and their nanocomposites were characterized by 1H-NMR and Fourier transform infrared spectroscopy, thermogravimetric analysis and gel permeation chromatography analysis. Additional information regarding some properties of these materials was obtained from the mechanical evaluation of thin films through stress–strain testing and dynamic mechanical analysis. Moreover, the effects of clay and interlayer ions on the morphology and physical properties of the hybrid nanocomposites were examined using atomic force microscope, X-ray diffractometer and transmission electron microscope.