ABSTRACT:Various segmented polyurethane materials with a polyurethane hard segment (HS) content of 40 wt % were prepared by bulk polymerization of a poly(tetramethylene ether) glycol with M n of 2000, 1,4-butanediol, and various diisocyanates. The diisocyanates used were pure 4,4Ј-diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (T100), toluene diisocyanate containing 80% 2,4-isomer and 20% 2,6-isomer (T80), isophorone diisocyanate (IPDI), hydrogenated 4,4Ј-diphenylmethane diisocyanate (HMDI), and 1,6-hexane diisocyanate (HDI). The segmented polyurethane materials were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile properties, tear strength, and Shore A hardness. The DSC and DMA data show that the thermal transitions are influenced significantly by the diisocyanate structure. In the segmented polyurethane materials with aliphatic HS, the polyether soft segment (SS) is immiscible with the HS. However, in the segmented polyurethane materials with aromatic HS, the SS is partially miscible with the HS. The diisocyanate structure also influences the mechanical properties significantly and is described as the effect of symmetry and chemical structure of the HS. Various solution polymerized polyurethane resins with solid content of 30 wt % were also prepared and their thickness retention, water resistance, and yellowing resistance were determined for the evaluation of their usage as wet process polyurethane leather. The polyurethane resin with aliphatic HS show poorer thickness retention but better yellowing resistance.

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.

Poly(ethylene terephthalate) (PET) sheets of different crystallinity were obtained by annealing the amorphous PET (aPET) sheets at 110 C for various times. The peaks of enthalpy recovery and double cold-crystallization in the annealed aPET samples with different crystallinity were investigated by a temperature-modulated differential scanning calorimeter (TMDSC) and a dynamic mechanical analyzer (DMA). The enthalpy recovery peak around the glass transition temperature was pronounced in TMDSC nonreversing heat flow curves and was found to shift to higher temperatures with higher degrees of crystallinity. The magnitudes of the enthalpy recovery peaks were found to increase with annealing times for samples annealed 30 min but to decrease with annealing times for samples annealed !40 min. The nonreversing curves also found that the samples annealed short times ( 40 min) having low crystallinity exhibited double cold-crystallization peaks (or a major peak with a shoulder) in the region of 108-130 C. For samples annealed long times (!50 min), the cold-crystallization peaks were reduced to one small peak or disappeared because of high crystallinity in these samples. The double cold-crystallization exotherms in samples of low crystallinity could be attributed to the superposition of the melting of crystals, formed by the annealing pretreatments, and the cold-crystallizations occurring during TMDSC heating. The ongoing crystallization after the cold crystallization was clearly seen in the TMDSC nonreversing heat flow curves. DMA data agreed with TMDSC data on the origin of the double cold-crystallization peaks.