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Hydrolytic Stability (hydrolytic + stability)
Selected AbstractsStudy of Different Substituted Cyclic and Acyclic Benzylpronucleotides of d4T Relative to Their Hydrolytic Stability and Antiviral ActivityCHEMINFORM, Issue 4 2004U. Muus Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Synthesis and Hydrolytic Stability of tert-Butoxydimethylsilyl Enol Ethers.CHEMINFORM, Issue 51 2001Zacharia A. Fataftah Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Effectiveness of caffeic acid as an anti-oxidant for cod liver oilINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2003Antonella De Leonardis Summary The effectiveness of caffeic acid and butylated hydroxyanisole (BHA) as anti-oxidants for cod liver oil was investigated. The phenol were added to oil in doses of 300, 600 and 800 mg kg,1 and the samples were oxidized at 100 °C in a rancimat apparatus. Caffeic acid not only improved oil stability, but also developed a further protective action which increased hydrolytic stability, inhibited diene conjugation and reduced losses of polyunsaturated fatty acid (PUFA)-n3. Caffeic acid showed a higher anti-oxidant effect than BHA. [source] Evaluation of performance of polyurethanes based on hydroxy alkylated cardanol formaldehyde resins under aging conditions,ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2004K. Sathiyalekshmi Abstract Rigid polyurethanes were synthesized using hydroxy alkylated cardanol formaldehyde and hydroxy alkylated dimerized-cardanol formaldehyde resins and dicyclo hexyl methane diisocyanate. The studies on the aging (hydrolytic stability, absorption of water/toluene, chemical resistance, dimensional stability, and thermal stability) of these polyurethanes reveal appreciable stability. The performance of these polyurethanes was compared with elastoplastic polyurethanes synthesized with the addition of commercially available poly(ethylene glycol). The rigid polyurethanes are distinctly stable than elastoplastic polyurethanes under various aging conditions. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 91,102, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20005 [source] Synthesis and comparative physicochemical investigation of partly aromatic cardo copolyestersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007N. B. Joshi Abstract Copolyesters were synthesized through the condensation of 0.0025 mol of 1,1,-bis(3-methyl-4-hydroxyphenyl)cyclohexane, 0.0025 mol of ethylene glycol/propylene glycol/1,4-butanediol/1,6-hexane diol, and 0.005 mol of terephthaloyl chloride with water/chloroform (4:1 v/v) as an interphase, 0.0125 mol of sodium hydroxide as an acid acceptor, and 50 mg of cetyl trimethyl ammonium bromide as an emulsifier. The reaction time and temperature were 2 h and 0°C, respectively. The yields of the copolyesters were 81,96%. The structures of the copolyesters were supported by Fourier transform infrared and 1H-NMR spectral data and were characterized with the solution viscosity and density by a floatation method (1.1011,1.2697 g/cm3). Both the intrinsic viscosity and density of the copolyesters decreased with the nature and alkyl chain length of the diol. The copolyesters possessed fairly good hydrolytic stability against water and 10% solutions of acids, alkalis, and salts at room temperature. The copolyesters possessed moderate-to-good tensile strength (11,37.5 MPa), good-to-excellent electric strength (19,45.6 kV/mm), excellent volume resistivity (3.8 × 1015 to 2.56 × 1017 , cm), and high glass-transition temperatures (148,195°C) and were thermally stable up to about 408,427°C in a nitrogen atmosphere; they followed single-step degradation kinetics involving 38,58% weight losses and 34,59% residues. The copolyesters followed 2.6,2.9-order degradation kinetics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Comparison of the hydrolytic stability of S -(N,N -diethylaminoethyl) isobutyl methylphosphonothiolate with VX in dilute solutionJOURNAL OF APPLIED TOXICOLOGY, Issue S1 2001M. D. Crenshaw Abstract The stability of S -(N,N -diethylaminoethyl) isobutyl methylphosphonothiolate,a V-type nerve agent developed by the former Soviet Union,in the environment is an important parameter in threat assessment analysis and for the determination of use, production, testing and storage of this chemical warfare agent. S -(N,N -Diethylaminoethyl) isobutyl methylphosphonothiolate is a structural isomer of the nerve agent VX developed by the USA and the UK and will be referred to as VXA (VX analog) in this presentation. Because VXA and VX differ structurally, even though they do have the same molecular formula, it is expected that their physical and chemical properties would be different. This preliminary investigation was undertaken to determine the relative hydrolysis rate of VXA compared with VX. The hydrolysis of each compound at approximately 1 mg ml,1 in unbuffered water at pH 7 was determined side-by-side. The half-lives for VXA and VX were determined to be 12.4 days and 4.78 days, respectively. Agent VXA hydrolyzed 2.6 times more slowly than VX, and each agent followed second-order hydrolysis kinetics. These results imply that VXA is more persistent in the environment and therefore poses a greater threat. These results also imply that VXA is more likely to be detected, if present, during an inspection in support of the Chemical Weapons Convention. Copyright © 2001 John Wiley & Sons, Ltd. [source] Cationic polymerization of L,L -lactideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2010gorzata Ba Abstract Cationic bulk polymerization of L,L- lactide (LA) initiated by trifluromethanesulfonic acid [triflic acid (TfA)] has been studied. At temperatures 120,160 °C, polymerization proceeded to high conversion (>90% within ,8 h) giving polymers with Mn , 2 × 104 and relatively high dispersity. Thermogravimetric analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)2 initiating system. Also hydrolytic stability of cationically prepared PLA was significantly higher than hydrolytic stability of linear PLA. Because thermal or hydrolytic degradation of PLA starting from end-groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer. High thermal and hydrolytic stability, in spite of moderate molecular weight of cationically prepared PLA, indicate that the fraction of end-groups is considerably lower than in linear PLA of comparable molecular weight. According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal OH and C(O)OSO2CF3 end-groups. The presence of those groups allows efficient end-to-end cyclization. Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2650,2658, 2010 [source] Synthesis and stability study of dental monomers containing methacrylamidoethyl phosphonic acidsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2007Xiaoming Xu Abstract Three new dental monomers containing methacrylamidoethyl phosphonic acids were synthesized. The structures of the synthesized monomers were determined with electrospray mass spectrometry (ESMS), Fourier transform infrared, and NMR. The hydrolytic stabilities of the synthesized monomers and a commercial monomer, 2-methacryloyloxyethyl phosphoric acid (MEP; used as a control), were studied with flow injection (FI)/ESMS, 1H NMR, and 31P NMR analysis of a CD3OD/D2O (4:1 v/v) solution of each monomer before and after storage at 60 °C for 2 months. The 1H NMR and 31P NMR chemical shifts of the monomers 2-methacrylamidoethylphosphonic acid (I) and N,N,-[4,4,-(propane-2,2-diyl)-bis(phenoxy-2-hydroxypropyl)]-bis(2-methacrylamidoethylphosphonic acid) (II) showed little change after storage at 60 °C for 2 months, but those of MEP changed significantly. FI/ESMS also showed that MEP was nearly completely decomposed, whereas monomers I and II remained largely intact. MEP could react with H2ZrF6 to form ternary zirconium fluoride complexes that were partially soluble in methanol, but all the monomers containing phosphonic acids formed precipitates. This study demonstrates that ESMS is a more sensitive and effective method than NMR for studying the hydrolytic stability or degradation of dental monomers. The new monomers containing methacrylamidoethyl phosphonic acids have higher hydrolytic stability than methacrylate phosphate monomers and may be used in dental bonding agents and other dental materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 99,110, 2007 [source] Synthesis and properties of polyimides bearing acid groups on long pendant aliphatic chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2006Tomohiro Yasuda Abstract A series of novel polyimide electrolytes having long pendant sulfo- or phosphoalkoxy groups were synthesized for fuel-cell applications. Sulfodecyloxy-, phosphodecyloxy-, and sulfophenoxydodecyloxy-substituted benzidine monomers were synthesized from dihydroxybenzidine. These monomers were copolymerized with naphthalene tetracarboxylic dianhydride and fluorenylidene dianiline to give the corresponding polyimides. A flexible, ductile, and self-standing membrane was obtained via casting from the polyimide solution. Because the acid groups were on long pendant side chains and away from the main chains, the polyimide membrane showed improved oxidative and hydrolytic stability in comparison with the polyimides with sulfonic acid groups on the main chains or on the short side chains. High thermal stability (no glass-transition temperature and a decomposition temperature > 200 °C) was also obtained. The polyimide membrane displayed high proton conductivity of 10,1 S cm,1 at 120 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3995,4005, 2006 [source] Structure,property correlations of sulfonated polyimides.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2004Abstract A series of six-membered sulfonated polyimides were synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4,-diaminobiphenyl 2,2,-disulfonic acid as the sulfonated diamine, and various nonsulfonated diamine monomers having different bridging groups. These bulky bridging groups have the capacity to increase hydrolytic stability and proton conductivity. Polyimides with bulky bridging groups showed increased solubility but exhibited lower thermal stability. The ion exchange capacity and water uptake reduced with increase in the bulkiness of the bridging group. This was attributed to the increase in the molecular weight of the repeating unit and hence effectively reduced the sulfonic acid content. In low temperatures, the conductivity was lower than Nafion®115 and, with increase in temperature, the conductivity rapidly increased and exhibited better conductivity than Nafion®115. Polyimides with bulky bridging groups 4-amino phenyl sulfone, and 2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane showed higher conductivity than other polyimides and Nafion®115 despite low ion exchange capacity. The hydrolytic stability of the polyimides with bulky bridging groups was higher than the polyimides with less bulky atoms because of the imparted flexibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3612,3620, 2004 [source] Sulfonated naphthalene dianhydride based polyimide copolymers for proton-exchange-membrane fuel cells.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2004Abstract A novel sulfonated diamine, 3,3,-disulfonic acid-bis[4-(3-aminophenoxy)phenyl]sulfone (SA-DADPS), was prepared from m -aminophenol and disodium-3,3,-disulfonate-4,4,-dichlorodiphenylsulfone. The conditions necessary to synthesize and purify SA-DADPS in high yields were investigated in some detail. This disulfonated aromatic diamine, containing ether and sulfone linkages, was used to prepare N -methyl-2-pyrrolidinone-soluble, six-membered ring polyimide copolymers containing pendent sulfonic acid groups by a catalyzed one-step high-temperature polycondensation in m -cresol. These materials showed much improved hydrolytic stability with respect to phthalimides. High-molecular-weight film-forming statistical copolymers with controlled degrees of disulfonation were prepared through variations in the stoichiometric ratio of disulfonated diamine (SA-DADPS) in its soluble triethylamine salt form to several unsulfonated diamines. Three unsulfonated diamines, bis[4-(3-aminophenoxy)phenyl] sulfone, 4,4,-oxydianiline, and 1,3-phenylenediamine, were used to prepare the copolymers. The characterization of the copolymers by 1H NMR, Fourier transform infrared, ion-exchange capacity, and thermogravimetric analysis demonstrated that SA-DADPS was quantitatively incorporated into the copolymers. Solution-cast films of the sulfonated copolymers were prepared and afforded tough, ductile membranes with high glass-transition temperatures. Methods were developed to acidify the triethylammonium salt membranes into their disulfonic acid form, this being necessary for proton conduction in a fuel cell. The synthesis and characterization of these materials are described in this article. Future articles will describe the performance of these copolymers as proton-exchange membranes in hydrogen/air and direct methanol fuel cells. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 862,874, 2004 [source] Impact of improved phosphite hydrolytic stability on the processing stabilization of polypropyleneJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2005Brian Johnson It is well known that some high-performance phosphite antioxidants are particularly sensitive to hydrolysis. This process has two principal consequences: 1) the creation of potential handling issues, as the product can become sticky, and 2) a possible loss in the performance of this type of antioxidant. In this article both of these are addressed. First, changes in the hydrolytic stability of a high-performance phosphite are examined by formulating with co-additives of different chemical natures. Second, changes in the hydrolytic stability of the phosphite when using different additive physical forms are investigated. Third, the influence of hydrolysis on the processing stabilization performance of the high-performance phosphite is evaluated. It is seen that the rate of hydrolysis of the high-performance phosphite is drastically reduced both by altering the physical form of the additive package and by the correct selection of the co-additive package. This selection not only extends the storage life of the high-performance phosphite but also minimizes the risk of any handling issues. Furthermore, it is concluded that hydrolysis does not necessarily mean a loss in performance but, contrary to general perception, can actually lead to an enhancement of the processing stability. The final conclusion of this study is that the hydrolysis mechanism of the phosphite is strongly influenced by the physical form of the additive package and by the chemical nature of the co-additives. This difference in mechanism is responsible for a different level of processing performance but is not discussed in detail in this publication. J. VINYL. ADDIT. TECHNOL. 11:136,142, 2005. © 2005 Society of Plastics Engineers. [source] Additive interactions in the stabilization of film grade high-density polyethylene.JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2002Part I: Stabilization, influence of zinc stearate during melt processing The melt stabilization activity of some of the most commercially significant phenolic antioxidants and phosphites (alone and in combination), without and with zinc stearate, was studied in high-density polyethylene (HDPE) produced by Phillips catalyst technology. Multiple pass extrusion experiments were used to degrade the polymer melt progressively. The effect of stabilizers was assessed via melt flow rate (MFR) and yellowness index (YI) measurements conducted as a function of the number of passes. The level of the phenolic antioxidant remaining after each extrusion was determined by high-performance liquid chromatography (HPLC). Phenolic antioxidants and phosphites both improved the melt stability of the polymer in terms of elt viscosity retention; the influence of zinc stearate was found to be almost insignificant. However, phosphites and zinc stearate decreased the discoloration caused by the phenolic antioxidants. A correlation was found between the melt stabilization performance of phosphites and their hydroperoxide decomposition efficiency determind via a model hydroperoxide compound. Steric and electronic effects associated with the phosphorus atom influenced the reactivity towards hydroperoxides. Furthermore, high hydrolytic stability did not automatically result in lower efficiency. Besides phosphite molecular structure, stabilization activity was also influenced by the structure of the primary phenolic antioxidant and the presence of zinc stearate. [source] | |||||||||||||