Two sets of polyether-polyurethane block polymers based on poly(tetramethylene oxide) (PTMO), 4,4'-methylenebis(phenyl isocyanate) (MDI), and butanediol (BD) were prepared in different ways to produce materials with equivalent stoichiometries but different hard segment length distributions. One set of materials was prepared by a one-step polymerization with butanediol as the chain extender. The second series was synthesized by a multistep method using butanediol and/or bis(4-hydroxybutyl) 4,4'-methylenebis(phenylcarbamate) (BMB) as the chain extender. The single-step polymers are shown to have fewer hard segments containing a single MDI unit than the corresponding multistep samples. The result of this is that the multistep materials exhibit a greater degree of phase mixing, as the very short hard segments are more likely to be dissolved in the soft phase than are longer hard segments. The evidence for this comes from the behavior of the sample ET-20M, an MDI/PTMO alternating copolymer. The hard phase volume fraction and crystallinity are greater in the single-step materials due to the lower degree of phase mixing in these polymers. The results of infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, stress-strain testing, and small-angle X-ray scattering are all shown to be consistent with the differences in hard segment length distributions and the differences in phase mixing which accompany the distributional differences. diffraction to study the crystal structure of MDI/BD/ PTMO-2000 polyurethanes. These materials had the same chemical constituents as those studied by Seymour et al.but had longer segmental lengths. Abouzahr found no detectable crystalline diffraction for samples with less than 35 wt % MDI. On the basis of small-angle X-ray scattering and stress relaxation studies, Abouzahr et al. also proposed that polyurethanes have an interlocked domain morphology at moderate MDI content (35 and 45 wt %).Bonart5,6 also examined the packing of MDI/BD hard segments using X-ray scattering and suggested that hard segments were laterally associated forming lamellae with a thickness limited by the average hard segment length. Using electron microscopy and X-ray diffraction analysis, Schneider et al.7 proposed that the MDI/BD hard segment domain existed in a micelle-like structure which was made

Abstract:The orientation behavior of two series of segmented polyether polyurethanes containing different hard segment length distributions has been studied as a function of the average hard segment length which was varied from one to five methylene bis (p-phenyl isocyanate) (MDI) units. The orientation behavior of the soft segments, isolated hard segments, and of hard segments aggregated in hard domains was determined from the dichroic behavior of representative infrared bands. As the hard segment length increases, a transition in orientation behavior is observed which corresponds to a change in sample morphology.The effects of annealing and hard segment length distribution were also studied and were shown to affect the orientation response through their influence on sample morphology. Orientation hysteresis studies were performed to probe the mechanism of the transverse orientation and orientation inversion which occurred in polyurethanes with the longer, more crystallizable hard segment lengths.

No abstract

SYNOPSISSilicone pressure-sensitive adhesives prepared from a platinum-catalyzed, high solids silicone composition are described. The adhesive compositions consist of an MQ siloxane resin, vinyl-and hydride-terminated silicone fluids, and a multifunctional vinyl silicone crosslinker. In this study, multifunctional vinyl silicone crosslinkers of various structures, including linear polymers, T, TQ, and Q resins, were prepared and evaluated for their effect on the adhesive properties of cured silicone pressure-sensitive adhesives. Additionally, the activity of these multifunctional vinyl silicones in hydrosilylation reaction was investigated.

synopsis Hard-segment model compounds containing one to five 4,l'-methylene bis@phenylisocyanate) (MDI) units extended with l,4-butanediol (BD) were synthesized. The ends of the model compounds were reacted with ethanol. The melting point (T,) of the model compounds increased with the number of MDI units to an extrapolated value of 299°C for the homopolymer using Flory's equation accounting for chain end defects. The A H of fusion was 5.3 kcal/mol. Intrinsic viscosity measurements in DMA solutions revealed a Mark Houwink exponent of 1.43 suggesting that the hard-segment model compounds are rodlike in solution. Wide-angle X-ray diffraction showed that the percentage of hard-segment crystallinity decreased as the oligomer length increased. Infrared spectroscopy studies showed that the distribution of hydrogen bond distances between C=O and NH groups became broader with increasing segment length.