Various segmented polyurethanes of different soft segment structure with hard segment content of about 50 wt% were prepared from 4,4 0 -diphenylmethane diisocyanate (MDI), 1,4-butanediol and different polyols with a M n of 2000 by a one-shot, hand-cast bulk polymerization method. The polyols used were a poly(tetramethylene ether)glycol, a poly(tetramethylene adipate)glycol, a polycaprolactonediol and two polycarbonatediols. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), UV-visible spectrometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC and DMA data indicate that the miscibility between the soft segments and the hard segments of the segmented polyurethanes is dependent on the type of the soft segment, and follows the order: polycarbonate segments > polyester segments > polyether segments. The miscibility between the soft segments and the hard segments plays an important role in determining the transparency of the segmented polyurethanes. As the miscibility increases, the transparency of the segmented polyurethanes increases accordingly. The segmented polyurethanes exhibit high elongation and show ductile behavior. The tensile properties are also affected by the type of the soft segment to some extent. POLYM. ENG. SCI.,

ABSTRACT:Various segmented polyurethanes with a hard segment content of about 50 wt% were prepared from 4,4 -diphenylmethane diisocyanate (MDI), a poly(tetramethylene adipate) glycol with an M n of 2000, and various combinations of aliphatic diols as chain extenders by a one-shot, hand-cast bulk polymerization method. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), ultraviolet-visible spectrometry, differential scanning calorimetry (DSC), and X-ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC data indicate rather good miscibility between the soft segments and the hard segments that accounts for the TRANSPARENT THERMOPLASTIC POLYURETHANES good transparency. The incorporation of a small amount of a second chain extender into MDI and 1-4-butanediol-based segmented polyurethanes decreases the crystallinity of the hard segment, thus enhancing the transparency. A segmented polyurethane derived from MDI and 1,6-hexanediol exhibits better transparency due to its relatively lower crystallinity of the hard segment.

Aqueous polyurethane dispersions derived from polycarbonatediols, isophorone diisocyanate, and carboxylic diols including dimethylol propionic acid and dimethylol butyric acid were prepared. The effect of dispersing procedure is investigated by FT IR, GPC, and the tensile film properties. The polyurethane dispersions prepared by a standard procedure exhibit lower molecular weights due to the overhydrolysis of the NCO groups. The polyurethane dispersions prepared by a modified procedure exhibit significantly higher molecular weights due to more effective chain extension, and their cast films exhibit higher tensile strength. The particle size, tensile properties, thermal properties, and dynamic mechanical properties are investigated. The chemical structure of the polycarbonatediols seems to affect the tensile strength. The glass transition temperature of the soft segments, T g (S), of the polyurethane dispersions can be seem from the DSC and DMA data.

Aqueous polyurethane dispersions derived from isophorone diisocyanate, various polycarbonatediols of different molecular weights, and dimethylol butyric acid were prepared by a dispersing procedure modified to enhance molecular weight. Particle size, average molecular weight, and tensile properties were determined. The molar ratio of reactants affected the properties of the polyurethane dispersions significantly, with the trends described as the effects of their ionic group and polycarbonatediol soft-segment contents. The molecular weight of the polycarbonatediols also significantly affected the particle size of the aqueous polyurethane dispersions and the film properties. As the molecular weight of the polycarbonatediols decreased, the particle size of the aqueous polyurethane dispersions decreased, and the moduli of the cast films increased, as expected. However, the tensile strength of the cast films decreased as the molecular weight of the polycarbonatediols decreased because of the decrease in elongation at break.

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