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Polyols
Terms modified by Polyols Selected AbstractsComposites of rigid polyurethane foam and cellulose fiber residueJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010M. C. Silva Abstract Rigid polyurethane composite foams were prepared with cellulose fibers as a filler. The cellulose fibers were an industrial residue of blanched cellulose pulp production. The influence of the cellulose fiber concentration on the structural, thermal, mechanical, and morphological properties of the foams was investigated. We also studied the influence of the cellulose fibers on the foam's resistance to fungal attack by placing a suspension of known fungus in contact with the surface of the foam and following the morphological evolution as a function of time (for 60 days). The increase in the cellulose filler concentration in the foams, up to 16% w/w with respect to the polyol, changed their properties as follows: (1) the cell size decreased, (2) the thermooxidative stability and mechanical properties remained approximately constant, (3) the thermal conductivity decreased slightly, and (4) fungal growth was observed. Therefore, a cellulosic fibrous industrial residue was rationally valorized as a filler in classical rigid polyurethane foams; this yielded materials with mechanical resistance and a susceptibility to fungi in a wet environment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Preparation and properties of waterborne interpenetrating polymer networks composed of polyurethaneurea and graft vinyl ester resinJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009Teng Su Abstract Various waterborne interpenetrating polymer networks (IPNs) composed of polyurethaneurea (PUU) and graft vinyl ester resin were prepared from polyester polyol, dimethylolpropionic acid, isophorone diisocyanate, ethylenediamine and a well-defined graft vinyl ester resin containing butanol side chains (BO-g-VER). These anionic IPN aqueous dispersions were stable at the ambient temperature for >1 yr, and also had the excellent stability at low and high temperatures. The experimental results showed that the introduction of BO-g-VER network has not only greatly affected the particle morphology, stability and rheological behavior of these aqueous dispersions, but also rendered the films with the augmented surface hydrophobicity as well as the excellent water-resistance performance and mechanical properties. A synergistic effect was observed at a certain BO-g-VER composition (20 wt %) to give significant reinforcement to the PUU, resulting from the compatibility and/or the interpenetration between the PUU network and the BO-g-VER network. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Polyurethane networks from different soy-based polyols by the ring opening of epoxidized soybean oil with methanol, glycol, and 1,2-propanediolJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Cheng-Shuang Wang Abstract A series of polyols with a range of hydroxyl (OH) numbers based on soybean oil and epoxidized soybean oil were prepared by oxirane ring opening with methanol, glycol, and 1,2-propanediol. The polyols, with average functionalities varying from 2.6 to 4.9, were characterized. Novel cast polyurethane resins were synthesized from these polyols and 2,4-toluene diisocyanate. The sol fraction of the network decreased as the OH number of the polyol from which it was synthesized increased. None of the samples were completely soluble. The crosslinking density of the polyurethanes correlated directly with the functionality of the polyols. The thermal and mechanical properties of the cast resins were characterized with differential scanning calorimetry and thermogravimetry. The glass-transition temperature increased with the OH number increasing, and the thermal stability of the resins was slightly decreased with the OH number increasing. The tensile strength at break increased with the OH number increasing. Polyurethanes prepared from polyols with OH numbers higher than 170 mg of KOH/g were glassy, whereas those with OH numbers below that value were rubbery. Glassy polyurethanes displayed decent mechanical strength, whereas rubbery samples showed relatively poor elastic properties and were characterized by lower strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Melt spun thermoresponsive shape memory fibers based on polyurethanes: Effect of drawing and heat-setting on fiber morphology and propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Jasmeet Kaursoin Abstract Thermoresponsive shape memory (SMP) fibers were prepared by melt spinning from a polyester polyol-based polyurethane shape memory polymer (SMP) and were subjected to different postspinning operations to modify their structure. The effect of drawing and heat-setting operations on the shape memory behavior, mechanical properties, and structure of the fibers was studied. In contrast to the as-spun fibers, which were found to show low stress built up on straining to temporary shape and incomplete recovery to the permanent shape, the drawn and heat-set fibers showed significantly higher stresses and complete recovery. The fibers drawn at a DR of 3.0 and heat-set at 100°C gave stress values that were about 10 times higher than the as-spun fibers at the same strain and showed complete recovery on repeated cycling. This improvement was likely due to the transformation brought about in the morphology of the permanent shape of the SMP fibers from randomly oriented weakly linked regions of hard and soft segments to the well-segregated, oriented and strongly H-bonded regions of hard-segments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2172,2182, 2007 [source] An improved OPLS,AA force field for carbohydratesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2002D. Kony Abstract This work describes an improved version of the original OPLS,all atom (OPLS,AA) force field for carbohydrates (Damm et al., J Comp Chem 1997, 18, 1955). The improvement is achieved by applying additional scaling factors for the electrostatic interactions between 1,5- and 1,6-interactions. This new model is tested first for improving the conformational energetics of 1,2-ethanediol, the smallest polyol. With a 1,5-scaling factor of 1.25 the force field calculated relative energies are in excellent agreement with the ab initio -derived data. Applying the new 1,5-scaling makes it also necessary to use a 1,6-scaling factor for the interactions between the C4 and C6 atoms in hexopyranoses. After torsional parameter fitting, this improves the conformational energetics in comparison to the OPLS,AA force field. The set of hexopyranoses included in the torsional parameter derivation consists of the two anomers of D -glucose, D -mannose, and D -galactose, as well as of the methyl-pyranosides of D -glucose, D -mannose. Rotational profiles for the rotation of the exocyclic group and of different hydroxyl groups are also compared for the two force fields and at the ab initio level of theory. The new force field reduces the overly high barriers calculated using the OPLS,AA force field. This leads to better sampling, which was shown to produce more realistic conformational behavior for hexopyranoses in liquid simulation. From 10-ns molecular dynamics (MD) simulations of ,- D -glucose and ,- D -galactose the ratios for the three different conformations of the hydroxymethylene group and the average 3JH,H coupling constants are derived and compared to experimental values. The results obtained for OPLS,AA,SEI force field are in good agreement with experiment whereas the properties derived for the OPLS,AA force field suffer from sampling problems. The undertaken investigations show that the newly derived OPLS,AA,SEI force field will allow simulating larger carbohydrates or polysaccharides with improved sampling of the hydroxyl groups. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1416,1429, 2002 [source] Modeling the dynamics of reactive foaming and film thinning in polyurethane foamsAICHE JOURNAL, Issue 2 2010G. Harikrishnan Abstract Flexible polyurethane foams are widely used in cushioning and packaging applications. A model for the dynamics of formation of polyurethane foams is presented, which includes thinning of foam lamellae. Experimental measurements for water blown flexible foam formulations at different water concentrations are presented to validate the model. Adiabatic temperature rise measurements during foaming are used to obtain the kinetic parameters of the reactions of isocyanate with polyol and water. The variation of foam density during foaming is studied by weight loss and video shooting methods and both are compared to estimate the amount of blowing gas lost during foaming. The average thickness of the foam lamellae of the solid foam is obtained by SEM measurements. The predictions of the model show good agreement with the experimental measurements of temperature and density with time and the final lamellar thickness. The results are important for understanding the cell opening process. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] NITZSCHIA OVALIS (BACILLARIOPHYCEAE) MONO LAKE STRAIN ACCUMULATES 1,4/2,5 CYCLOHEXANETETROL IN RESPONSE TO INCREASED SALINITY,JOURNAL OF PHYCOLOGY, Issue 2 2009Fernando Garza-Sánchez The growth of microalgae in hypersaline conditions requires that cells accumulate osmoprotectants. In many instances, these are polyols. We isolated the diatom Nitzschia ovalis H. J. Arn. from the saline and alkaline water body Mono Lake (CA, USA). This isolate can grow in salinities ranging from 5 to 120 parts per thousand (ppt) of salt but normally at 90 ppt salinity. In this report, we identified the major polyol osmoprotectant as 1,4/2,5 cyclohexanetetrol by electron ionization-mass spectrometry (EI,MS), 1H, 13C nuclear magnetic resonance spectroscopy (NMR), and infrared (IR) and showed an increase in cellular concentration in response to rising salinity. This increase in the cyclitol concentration was evaluated by gas chromatography of the derived tetraacetylated cyclohexanetetrol obtaining an average of 0.7 fmol · cell,1 at 5 ppt and rising to 22.5 fmol · cell,1 at 120 ppt. The 1,4/2,5 cyclohexanetetrol was also detected in the red alga Porphyridium purpureum. Analysis of the free amino acid content in N. ovalis cultures exposed to changes in salinity showed that proline and lysine also accumulate with increased salinity, but the cellular concentration of these amino acids is about 10-fold lower than the concentration of 1,4/2,5 cyclohexanetetrol. The comparison of amino acid concentration per cell with cyclitol suggests that this polyol is important in compensating the cellular osmotic pressure due to increased salinity, but other physiological functions could also be considered. [source] Poly(tetramethylene ether) glycol containing acetal linkages: New PTMG-based polyol for chemically recyclable polyurethane thermoplastic elastomerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2008Tamotsu Hashimoto To develop new chemically recyclable polyurethane elastomers, the poly(tetramethylene ether) glycol (PTMG) containing acetal linkages (PTMG-Acetal-OH) was prepared and subjected to the polyurethane synthesis with 4,4(-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD; chain-extender). The obtained polyurethane (PTMG-Acetal-PU) shows very similar mechanical and thermal properties to those of the conventional PTMG-based thermoplastic polyurethane elastomers (PTMG-PU). The acid treatment of PTMG-Acetal-PU at room temperature caused hydrolysis reaction of their acetal units to regenerate PTMG as a degradation product. [source] Semibatch emulsion polymerization of methyl methacrylate using different polyurethane particlesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2005ebenik Abstract Aqueous acrylic-polyurethane (AC,PU) hybrid emulsions were prepared by semibatch emulsion polymerization of methyl methacrylate (MMA) in the presence of four polyurethane (PU) dispersions. The PU dispersions were synthesized with isophorone diisocyanate (IPDI), 1000 and 2000 molecular weight (MW) poly(neopentyl) adipate, 1000 MW polytetramethyleneetherglycol, butanediol (BD), and dimethylol propionic acid (DMPA). MMA was added in the monomer emulsion feed. We studied the effect of the use of different PU seed particles on the rate of polymerization, the particle size and distribution, the number of particles, and the average number of radicals per particle. The PU rigidity was controlled by varying the polyol chemical structure, the polyol MW (Mn), and by adding BD. The monomer feed rate was varied to study its influence on the process. It was observed that the PU particles that had been prepared with a higher MW polyol swelled better with MMA before the monomer-starved conditions occurred. There seemed to be no significant discrepancies between the series with different PU seeds in the monomer-starved conditions. The overall conversion depended on the monomer addition rate, and the polymerization rate acquired a constant value that was comparable to the value of the monomer addition rate. The instantaneous conversion increased slightly. The average particle size increased, and the total particle number in the reactor was constant and similar to the number of PU particles in the initial charge. The average number of radicals per particle increased. The differences between the system with a constant particle number and average number of radicals per particle and the system with a fixed radical concentration are discussed. The semibatch emulsion polymerization of MMA in the presence of PU particles studied was better compared to the system with a fixed radical concentration. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 844,858, 2005 [source] Synthesis and characterization of polyurethane,urea nanoparticles containing methylenedi- p -phenyl diisocyanate and isophorone diisocyanateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2004In Woo Cheong Abstract Water-based polyurethane,urea (WPUU) nanoparticles containing 4,4,-methylenedi- p -phenyl diisocyanate (MDI) and isophorone diisocyanate (IPDI) were synthesized by a stepwise prepolymer mixing process, that is, the consecutive formation of hydroxyl-terminated and isocyanate-terminated polyurethane prepolymers. The reaction behavior, chemical structure, and consequent morphology of the polyurethane prepolymers and WPUU were investigated with Fourier transform infrared (FTIR), gel permeation chromatography, and NMR techniques with MDI concentrations ranging from 0 (pure IPDI) to 50% with respect to the total moles of isocyanate. Wide-angle X-ray diffraction and differential scanning calorimetry patterns showed that the crystallinity of WPUU, which mostly originated from crystallizable poly(tetramethylene adipate) polyol, was significantly affected by the MDI content. Both the crystallinity and melting temperature of WPUU decreased as the MDI content increased. Deconvoluted relative peak areas of the carbonyl region in the FTIR spectrum revealed that the effect of hydrogen bonding among the hard segments became favorable as the MDI content increased, whereas the hydrogen bonding of the soft segments significantly decreased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4353,4369, 2004 [source] Preparation of high-temperature polyurethane by alloying with reactive polyamideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Tsutomu Takeichi Abstract A series of novel poly(urethane amide) films were prepared by the reaction of a polyurethane (PU) prepolymer and a soluble polyamide (PA) containing aliphatic hydroxyl groups in the backbone. The PU prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate and then was end-capped with phenol. Soluble PA was prepared by the reaction of 1-(m -aminophenyl)-2-(p -aminophenyl)ethanol and terephthaloyl chloride. The PU prepolymer and PA were blended, and the clear, transparent solutions were cast on glass substrates; this was followed by thermal treatments at various temperatures to produce reactions between the isocyanate group of the PU prepolymer and the hydroxyl group of PA. The opaque poly(urethane amide) films showed various properties, from those of plastics to those of elastomers, depending on the ratio of the PU and PA components. Dynamic mechanical analysis showed two glass-transition temperatures (Tg's), a lower Tg due to the PU component and a higher Tg due to the PA component, suggesting that the two polymer components were phase-separated. The rubbery plateau region of the storage modulus for the elastic films was maintained up to about 250 °C, which is considerably higher than for conventional PUs. Tensile measurements of the elastic films of 90/10 PU/PA showed that the elongation was as high as 347%. This indicated that the alloying of PU with PA containing aliphatic hydroxyl groups in the backbone improved the high-temperature properties of PU and, therefore, enhanced the use temperature of PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3497,3503, 2002 [source] Physicochemical properties and application of pullulan edible films and coatings in fruit preservationJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2001Tony Diab Abstract The effects of water, sorbitol and a sucrose fatty acid ester (SE) on the water sorption behaviour and thermal and mechanical properties of pullulan-based edible films as well as the physiological responses of fruit coated with pullulan have been studied. Incorporation of sorbitol or SE in pullulan films resulted in lower equilibrium moisture contents at low to intermediate water activities (aw), but much higher moisture contents at aw,>,0.75; estimates of monolayer values (within 4.1,5.9,gH2O,kg,1 solids) were given by application of the Brunauer,Emmett,Teller (BET) and Guggenheim,Anderson,DeBoer (GAB) models. A single glass,rubber transition (Tg), attributed to the polysaccharide component, was detected by calorimetry and dynamic mechanical thermal analysis (DMTA) at a sorbitol level of 15,30% DM. With both tests the strong plasticising action of water and polyol was evident in the thermal curves, and the Tg vs moisture content data were successfully fitted to the Gordon,Taylor empirical model. Multifrequency DMTA measurements provided estimates for the apparent activation energy of the glass transition in the range of , 300,488,kJ,mol,1. With large-deformation mechanical testing, large decreases in Young's moduli (tensile and three-point bend tests) were observed as a result of water- and/or polyol-mediated glass-to-rubber transition of the polymeric films. In the moisture content range of 2,8%, increases in flexural modulus (E) and maximum stress (,max) with small increases in moisture content were found for films made of pullulan or pullulan mixed with 15% DM sorbitol; a strong softening effect was observed when the water content exceeded this range. Addition of sorbitol increased the water vapour transmission rate of the films, whereas addition of SE had the opposite effect. Application of a pullulan/sorbitol/SE coating on strawberries resulted in large changes in internal fruit atmosphere composition which were beneficial for extending the shelf-life of this fruit; the coated fruit showed much higher levels of CO2, a large reduction in internal O2, better firmness and colour retention and a reduced rate of weight loss. In contrast, similar studies on whole kiwifruits showed increased levels of internal ethylene, which caused acceleration of fruit ripening during storage. © 2001 Society of Chemical Industry [source] Silica Reinforced Organic,Inorganic Hybrid Polyurethane Nanocomposites From Sustainable ResourceMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2010Deewan Akram Abstract Polyol/nanosilica organic,inorganic hybrids (Si/Lpol) were prepared through facile sol,gel chemistry. Tetraethoxyorthosilane (TEOS) and linseed polyol (Lpol) obtained by hydroxylation of linseed oil were used as inorganic and organic precursors, respectively. Si/Lpol was further treated with toluene-2,4-diisocyanate (TDI) to obtain silica embedded polyurethane (Si/LPU). The structure of the organic,inorganic hybrid was confirmed by FTIR, 1H NMR, and 13C NMR spectral analysis. The polyol/nanosilica network shows strong interaction with the remnant polyol backbone through hydrogen bonding, which also has bearing on Tg of polymers. Morphological studies of Si/LPU show the formation of uniform, spherical silica nanoparticles of 2,30,nm size embedded in the polymer matrix. Si/LPU was further reinforced with 2 and 5,wt.-% fumed silica (FS-Si/LPUs); their morphology revealed a carpet layer formation on top of Si/LPU. Thermogravimetric analysis showed improved thermal stability of Si/LPU and FS-Si/LPUs. The polymers exhibit mild to moderate antibacterial behavior against E. coli and S. aureus, respectively, and will pave way in plethora of biological and chemical applications as coating materials. [source] Study of Polyurethane Formulations Containing Diols Obtained via Glycolysis of Poly(ethylene terephthalate) (PET) by Oligoesters Diols through a Reactive Extrusion ProcessMACROMOLECULAR MATERIALS & ENGINEERING, Issue 7 2005Gaël Colomines Abstract Summary: The glycolysis of PET by oligoester diols in the presence of zinc acetate was carried out in two successive twin-screw extruders with total residence times of 4 min and without solvent. These new glycolysates were analyzed and used in polyurethane formulation with a commercial polyol. The reactivity of these formulations was studied. The mechanical properties, thermal and swelling behavior of these polyurethanes were investigated. Mechanical properties are improved with the addition of glycolysate. The thermal behavior is not modified with the addition of glycolysate. The swelling behavior of the material depends on the solvent nature. The addition of glycolysate allows a decrease in material swelling in chloroform but increases this swelling in acetone. [source] Highly crystalline cobalt nanowires with high coercivity prepared by soft chemistryPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2009G. Viau Abstract Cobalt nanorods and wires were prepared by reduction of a cobalt salt in a liquid polyol. These particles crystallize with the hcp structure and the growth axis is parallel to the crystallographic c -axis. The kinetic control of the growth allows to vary the mean diameter of the rods and their aspect ratio. Dumbbell like shape particles consisting of a central rod with two conical tips were also obtained. Magnetization curves of oriented wires present very high coercivity (up to 9 kOe) resulting from both a high shape anisotropy and the high magnetocrystalline anisotropy of the hcp cobalt. Micromagnetic simulations showed that the magnetization reversal is shape dependent. The conical tips of the dumbbell particles strongly contribute to the coercivity decrease and must be precluded for permanent magnet applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of nickel,zinc ferrite nanoparticles in polyol: morphological, structural and magnetic studiesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2006Z. Beji Abstract Nickel,zinc ferrite monodisperse nanoparticles are synthesized by forced hydrolysis in diethylenglycol. FC and ZFC susceptibility curves suggest that they present superparmagnetic behaviour with a blocking temperature between 63 and 15 K depending on the zinc content. The saturation magnetization of the nanocrystals at 5 K is very close to that of bulk materials, and very high compared to that of similar particles prepared by other chemical routes. High Resolution Transmission Electron Microscopy and In-field Mössbauer studies show clearly that these relatively high values are mainly due to: (i) the high crystalline quality of the particles and (ii) a cation distribution different from the classical distribution encountered in the bulk material. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Formation and characterization of polyurethane,vermiculite clay nanocomposite foamsPOLYMER ENGINEERING & SCIENCE, Issue 9 2008T. Umasankar Patro Nanocomposites of rigid polyurethane foam with unmodified vermiculite clay are synthesized. The clay is dispersed either in polyol or isocyanate before blending. The viscosity of the polyol is found to increase slightly on the addition of clay up to 5 pphp (parts per hundred parts of polyol by weight). The gel time and rise time are significantly reduced by the addition of clay, indicating that the clay acts as a heterogeneous catalyst for the foaming and polymerization reactions. X-ray diffraction and transmission electron microscopy of the polyurethane composite foams indicate that the clay is partially exfoliated in the polymer matrix. The clay is found to induce gas bubble nucleation resulting in smaller cells with a narrower size distribution in the cured foam. The closed cell content of the clay nanocomposite foams increases slightly with clay concentration. The mechanical properties are found to be the best at 2.3 wt% of clay when the clay is dispersed in the isocyanate; the compressive strength and modulus normalized to a density of 40 kg/m3 are 40% and 34% higher than the foam without clay, respectively. The thermal conductivity is found to be 10% lower than the foam without clay. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Relationship between segment structures and elastic properties of segmented poly(urethane-urea) elastic fibersPOLYMER ENGINEERING & SCIENCE, Issue 11 2003Nori Yoshihara Studies on segmented poly(urethane-urea) (SPUU) elastic fibers having various segment structures were done in terms of elastic recovery and stress-strain relationship (S-S). Three kinds of segment structures were used: 1) the same composition having different sequences of segment units, 2) the same length of soft segments having different molecular weights of polyol, and 3) different segment structures having almost the same stress at 350% elongation. The SPUU elastic fibers having higher sequence numbers of both soft and hard segment units, that is, greater block structures, show better elastic recovery properties, especially delayed elastic recovery. The SPUU elastic fibers showing better elastic recovery take an optimum value for the number-average molecular weight (Mn) of soft segments jointed with urethane bonds. Here the optimum Mn depends on the molecular weight of polytetramethyleneglycol (PTMG) as a starting material. The hysteresis loss in S-S for the pre-elongation decreases with an increase of Mn of PTMG. The SPUU elastic fibers having greater block structures show lower stress with lower 2C1 and 2C1 + 2C2 of Mooney-Rivilin plot constants for elastic fibers having the same composition. This indicates a lower density of crosslinks for finite deformation. An increase of the urea bonds or the molar ratio of urea bond to urethane bond raises the stress. It is found that the polymerization process, as well as composition, is important for design structures of SPUU elastic fibers. [source] Structure-property relationship in polyurethane elastomers containing starch as a crosslinkerPOLYMER ENGINEERING & SCIENCE, Issue 5 2000Sonal Desai Polyurethane elastomers were synthesized using polypropylene glycol (PPG 2000) as the polyol and starch as the multifunctional crosslinker in varying concentrations. Thermal and mechanical properties were measured by DSC, DMA and tensile tests. The morphology was examined by SEM. The swelling behavior of the polyurethanes in various solvents was investigated and the solubility parameter was determined. All these properties were compared with those of polyurethanes containing 1,1,1 -trimethylol propane (TMP) as the crosslinker. Starch-based polyurethanes exhibited better mechanical properties. The effect of varying the starch:TMP ratio on the mechanical strength was also studied. With increasing starch content, the tensile strength and elongation increased. The starch-based PUs exhibited two glass transitions, whereas TMP-based PUs exhibited one Tg. No significant difference in the Tgs of the two PUs was observed. The activation energy of St-PU calculated from DMA was 69 kcal/mol. Soil degradation tests indicated greater biodegradability in polyurethanes containing starch than in those containing TMP. [source] Intercalation and exfoliation behaviour of clay layers in branched polyol and polyurethane/clay nanocompositesPOLYMER INTERNATIONAL, Issue 2 2006Hesheng Xia Abstract The exfoliation of clay layers was realized in a tri-hydroxyl branched polyether polyol by direct mixing and the corresponding exfoliated polyurethane/clay nanocomposite was prepared by further in situ curing. The effects of various surface-modified organoclays and various polyol types on the intercalation and exfoliation behaviour of clay layers were investigated. The interaction between the polyol and clay and the mixing temperature plays an important role in the occurrence of exfoliation and intercalation. The relationship between rheological data of polyol/clay dispersion and the intercalation or exfoliation state of the clay was established. This provides a convenient and efficient way to evaluate the dispersion state of the clay. Based on the experimental results, a possible layer-by-layer exfoliation mechanism is proposed. Copyright © 2006 Society of Chemical Industry [source] Fireproofing of polyurethane elastomers by reactive organophosphonatesPOLYMER INTERNATIONAL, Issue 1 2003Wassef El Khatib Abstract Polyurethane elastomers were prepared with hydroxytelechelic polybutadiene (HTPB) as polyol, modified 4,4,-diphenylmethane diisocyanate (modified MDI) as liquid polyisocyanate, and phosphonate diols as chain extenders and flame retardant compounds. These phosphonate diols were synthesized by radical thiol,ene addition of allyl or vinyl dialkyl phosphonate to 3-mercapto-1,2-propanediol. For various percentages of phosphorus (0 to 3%, w/w), polyurethane elastomers remain stable up to 250,°C. The percentage of residual char at 600,°C increases with increasing phosphorus content. For the soft segments, no variation in the glass transition temperature (Tg) is observed as the percentage of P increases, whereas the Tg of hard segments increases. Above 0.5% phosphorus content, the limiting oxygen index (LOI) becomes higher than the percentage of oxygen in the air. © 2003 Society of Chemical Industry [source] Effects of surfactant and molecular weight of polyol on grating formation and switching of holographic PDLCPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11 2008S. S. Shim Abstract The interposition of surfactants between polymer and liquid crystal (LC) droplets was theoretically predicted by the positive spreading coefficient (0,<,,31) and utilized to interpret the morphology, grating formation kinetics, diffraction efficiency, and switching of the holographic polymer dispersed liquid crystal (HPDLC), prepared from various types (octanoic acid, poly oxyethylene octyl phenyl ether, and perfluoro-1-butanesulfonyl fluoride) and amounts (0,9 wt%) of surfactant and molecular weights of polyol (PPG). Regardless of the surfactant type, diffraction efficiency increased with the addition and increasing amount of surfactant, a tendency consistent with increasing value of spreading coefficient, which is determined by the formulations of grating formation. In contrast, diffraction efficiency showed a maximum with the polypropylene glycol (PPG) molecular weight. Surfactant effectively reduced the anchoring energy and electrically drove the film which otherwise was not driven. Overall, surfactant with greater ,31 gave smaller droplet, greater diffraction efficiency, driving voltage, contrast ratio, and smaller response time. Copyright © 2008 John Wiley & Sons, Ltd. [source] Stereocontrolled Synthesis of the C21,C38 Fragment of the Unnatural Enantiomer of the Antibiotic Nystatin A1CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2004Thilo Berkenbusch Dr. Abstract The C21,C38 fragment all- trans - 41 of the unnatural enantiomer 1 of nystatin A1 was prepared starting from the N -propionyl oxazolidinone 9. Aldol adduct ent - 8 (ee > 96,%) derived in two steps was hydroborated with (thexyl)BH2. Oxidative work-up and treatment with acid furnished ,-lactone 4. It contains the complete stereotetrade of the target molecule. The ,,,-unsaturated ester 28 was reached after another four steps. It should be a precursor for the polyene moieties of a variety of polyol,polyene macrolides. Illustrating that, the ,,,-unsaturated aldehyde 29 obtained from 28 and DIBAL was extended by 10 C atoms in four steps yielding the C21,C38 segment 41. The latter set of transformations included the regio- and stereoselective Claisen rearrangement 32,35. [source] Crystal Structures of Conformationally Locked Cyclitols: An Analysis of Hydrogen-Bonded Architectures and their Implications in Crystal EngineeringEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2007Goverdhan Mehta Abstract A qualitative study has been carried out on selected polycyclitols to evaluate the potential of conformational locking of hydroxy groups in lending predictability to the O,H···O hydrogen-bonding network observed in the crystal structures of such compounds. The polycyclitols employed in this study are conformationally locked with all the hydroxy groups destined to be axial owing to the trans ring fusion(s) in the polycyclic carbon framework. The consequent formation of intramolecular O,H···O hydrogen bonds between the 1,3- syn diaxial hydroxy groups now permits any packing pattern in the polycyclitols to be described in terms of a small group of intramolecularly bonded molecular motifs linked to their respective neighbors by four O,H···O bonds. By using this model and the results of CSD analyses of polyols as a guide, the O,H···O hydrogen-bonded packing motifs most likely to be observed in the crystal structure of each polycyclitol were proposed and compared with those obtained experimentally. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A Versatile Solvent-Free "One-Pot" Route to Polymer Nanocomposites and the in situ Formation of Calcium Phosphate/Layered Silicate Hybrid NanoparticlesADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Hans Weickmann Abstract Poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyurethane (PU) nanocomposites containing well-dispersed calcium phosphate/layered silicate hybrid nanoparticles were prepared in a versatile solvent-free "one-pot" process without requiring separate steps, such as organophilic modification, purification, drying, dispersing, and compounding, typical for many conventional organoclay nanocomposites. In this "one-pot" process, alkyl ammonium phosphates were added as swelling agents to a suspension of calcium/layered silicate in styrene, methyl methacrylate, or polyols prior to polymerization. Alkyl ammonium phosphates were prepared in situ by reacting phosphoric acid with an equivalent amount of alkyl amines such as stearyl amine (SA) or the corresponding ester- and methacrylate-functionalized tertiary alkyl amines, obtained via Michael Addition of SA with methyl acrylate or ethylene 2-methacryloxyethyl acrylate. Upon contact with the calcium bentonite suspension, the cation exchange of Ca2+ in the silicate interlayers for alkyl ammonium cations rendered the bentonite organophilic and enabled effective swelling in the monomer accompanied by intercalation and in situ precipitation of calcium phosphates. According to energy dispersive X-ray analysis, the calcium phosphate precipitated exclusively onto the surfaces of the bentonite nanoplatelets, thus forming easy-to-disperse calcium phosphate/layered silicate hybrid nanoparticles. Incorporation of 5,15,wt% of such hybrid nanoparticles into PMMA, PS, and PU afforded improved stiffness/toughness balances of the polymer nanocomposites. Functionalized alkyl ammonium phosphate addition enabled polymer attachment to the nanoparticle surfaces. Transmission electron microscopy (TEM) analyses of PU and PU-foam nanocomposites, prepared by dispersing hybrid nanoparticles in the polyols prior to isocyanate cure, revealed the formation of fully exfoliated hybrid nanoparticles. [source] The osmotic stress tolerance of basidiomycetous yeastsFEMS YEAST RESEARCH, Issue 4 2010Obakeng M. Tekolo Abstract The growth and accumulation of intracellular polyols at reduced water activity (aw) were studied in 40 basidiomycetous yeast strains. The growth of most strains showed greater tolerance to NaCl than sorbitol at the same aw. No strain was able to grow below 0.90aw. 13C nuclear magnetic resonance spectroscopy revealed that glycerol was the major solute accumulated intracellularly by all the yeasts when grown to 0.96aw (NaCl). Arabitol or mannitol was also accumulated in some yeasts, whereas a few only accumulated glycerol. Analysis of six yeasts in detail revealed that the intracellular glycerol concentrations of five yeasts increased significantly when grown at 0.96aw (NaCl or sorbitol) compared with growth at 0.998aw. Arabitol and mannitol concentrations also increased, but not to the same degree. Intracellular potassium concentrations decreased when grown at 0.96aw (NaCl or sorbitol) and sodium increased, but only when grown at 0.96aw (NaCl). The survival of nine strains was evaluated in soil cultures and it was found that all grew at 100% field capacity, whereas at lower field capacity, only some strains grew or survived. The growth of basidiomycetous yeasts appears to be more sensitive to reduced aw than ascomycetous yeasts. [source] Aspergillus oryzae in solid-state and submerged fermentationsFEMS YEAST RESEARCH, Issue 2 2002Progress report on a multi-disciplinary project Abstract We report the progress of a multi-disciplinary research project on solid-state fermentation (SSF) of the filamentous fungus Aspergillus oryzae. The molecular and physiological aspects of the fungus in submerged fermentation (SmF) and SSF are compared and we observe a number of differences correlated with the different growth conditions. First, the aerial hyphae which occur only in SSFs are mainly responsible for oxygen uptake. Second, SSF is characterised by gradients in temperature, water activity and nutrient concentration, and inside the hyphae different polyols are accumulating. Third, pelleted growth in SmF and mycelial growth in SSF show different gene expression and protein secretion patterns. With this approach we aim to expand our knowledge of mechanisms of fungal growth on solid substrates and to exploit the biotechnological applications. [source] Dehydration tolerance and water vapour absorption in two species of soil-dwelling Collembola by accumulation of sugars and polyolsFUNCTIONAL ECOLOGY, Issue 5 2001M. Holmstrup Summary 1,Physiological and biochemical responses to desiccation were studied in two species of hygrophilic Collembola, Folsomia fimetaria L. and Protaphorura armata Tullberg. The temporal changes in water content, body fluid osmotic pressure, and accumulation of sugars and polyols during desiccation stress, equivalent to severe soil drought are reported. 2,Both species initially lost about 50% of their initial content of osmotically active water. Within 7 days F. fimetaria had re-established their preliminary water content by absorbing water vapour from the atmosphere. Protaphorura armata also significantly increased their water content over the following 10 days. 3,Both species were able to resume their hyperosmotic status relative to the desiccating environment they were placed in. The accumulation of myo-inositol and two other unidentified compounds (F. fimetaria) and trehalose (P. armata) made an important contribution to this phenomenon. 4,These results suggest that water vapour absorption by accumulation of sugars and polyols may be widespread in soil-dwelling Collembola. [source] Regio- and Stereoselective Intermolecular Hydroalkoxylation of Alkynes Catalysed by Cationic Gold(I) ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Avelino Corma Abstract Vinyl ethers and ketals are obtained from the reaction of phenylacetylene derivatives and dimethyl acetylenedicarboxylate (DMAD) with alcohols in good yields and levels of stereoselectivity by using cationic gold(I)-phosphine complexes as catalysts. By choosing the appropriate phosphine, the selective formation of the Z or the E isomer of the vinyl ether can be tuned, and the undesired formation of the ketal can be controlled. The isomerisation of fumarates (Z -isomer) to maleates (E -isomer) is a gold-catalysed process that can be conducted in one-pot. When using polyols, 5-membered cyclic ketals are easily isolated by extraction with hexane and the gold complex can be reused. [source] An in vitro study of the pH-lowering potential of salivary lactobacilli associated with dental cariesJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2001M.C. Badet M.C. BADET, B. RICHARD AND G. DORIGNAC. 2001. Aims: Lactobacilli are known to produce acids from sucrose or glucose. This acid production can cause a drop in pH which is sufficiently significant to demineralize the hard tissues of the teeth. Some authors have demonstrated the benefits of substituting sorbitol or xylitol for sucrose. The aim of this work was to study the acid production of salivary lactobacilli with one test sugar (glucose) and two polyols (sorbitol and xylitol). Methods and Results: The pH-lowering potential of three strains of oral lactobacilli was recorded with glucose or one of the polyols at three different concentrations. The results showed that polyols were broken down by certain strains of lactobacilli. When this degradation took place, the pH dropped to values sufficiently low to demineralize the hard tissues of the teeth. Conclusions: Further studies must be carried out on the metabolism of polyols before encouraging their widespread substitution for sucrose. [source] | ||||||||||||||||