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G. Liptay J. Nagy A. Borbély-Kuszmann J. Ch. Weis 《Journal of Thermal Analysis and Calorimetry》1987,32(6):1683-1691
It was proved experimentally that isotherms obtained from the results of isothermal thermogravimetric analysis are suitable for the characterization of silicone rubbers used in industry. The experimental results provide a possibility for the calculation of overall (apparent) reaction rate constants, characteristic of the thermal decomposition process, and for the calculation of half-life values in conjunction with the service life. Comparisons of the isotherms and of the characteristic calculated values demonstrated the effects of the parameters of silicone rubber preparation and of the conditions of application on the thermal stability.
Zusammenfassung Es wurde experimentell nachgewiesen, daß die auf der Basis der Ergebnisse von isothermen thermogravimetrischen Untersuchungen gewonnen Isothermen zur Charakterisierung von industriell angewandten Silicongummis geeignet sind. Die experimentellen Ergebnisse ermöglichen einerseits die Berechnung einer für den thermischen Zersetzungsprozeß charakteristischen resultierenden Reaktionsgeschwindigkeitskonstanten und andererseits die Berechnung von Halbwertszeiten hinsichtlich der Gebrauchsdauer. Der Vergleich der Isothermen mit den errechneten charakteristischen Werten veranschaulicht den Einfluß der Parameter bei der Herstellung von Silicongummis und den Einfluß der Anwendungsbedingungen auf die thermische Stabilität.
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Liptay G. Nagy J. Weis J. Ch. Borbély-Kuszmann A. 《Journal of Thermal Analysis and Calorimetry》1987,32(5):1421-1433
The investigations proved that isothermal thermogravimetry yields useful information on the thermal stability of silicone caoutchouc and silicone rubber. It was established that the thermal degradation is a first-order reaction. Measurements and calculations verified that in multicomponent systems the resultant degradation curve obtained by isothermal measurements is formed additively from the degradation curves of the components, i.e. the thermal decompositions of the components proceed independently of one another.
Zusammenfassung Die isotherme Thermogravimetrie liefert nützliche Informationen über die thermische Stabilität von Silkonkautschuk und Silikongummi. Der thermische Abbau verläuft nach einer Reaktion erster Ordnung. Messungen und Berechnungen haben bestätigt, daß in Vielkomponentensystemen die resultierende isotherme Zersetzungskurve sich additiv aus den Zersetzungskurven der Komponenten zusammensetzt, d. h., daß die thermische Zersetzung der Komponenten unabhängig voneinander verläuft.
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A series of polyureas were synthesized from amino terminated polydimethylsiloxane oligomers of different molecular weight and various diisocyanates. These polymers were characterized by nuclear magnetic resonance (NMR), infrared (IR) spectroscopy and size exclusion chromatography (SEC). The formation of hydrogen bonding of the urea segments was investigated by temperature dependent IR-spectroscopy. The gelation behavior in silicone fluids such as dimethylcyclosiloxanes was investigated. The influence of the structure of the hard and the soft segment on the gelation properties was evaluated. 相似文献
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Yong Guan Huanyao Zhang Anna Zheng Dafu Wei Jian Hu Zhenzhen Wang Xiang Xu 《先进技术聚合物》2019,30(7):1555-1563
Recently, silicone rubber (VMQ) was extensively used in household articles and medical devices. To develop a kind of safe and long‐term antimicrobial VMQ was of great significance. In this work, a kind of vinyl‐contained polyhexamethylene guanidine hydrochloride (VPHMG) was synthesized and used as antimicrobial additive for VMQ. With the increasing of VPHMG addition, the mechanical properties and antimicrobial properties of VMQ‐VPHMG were significantly improved. In particular, the antimicrobial rates against Escherichia coli and Staphylococcus aureus were higher than 99.99% as for 4 wt% of VPHMG addition. Moreover, the surface concentration of VPHMG as well as the antimicrobial rates revealed almost unchanged after being extracted by water and methanol. All the results indicated the vinyl‐contained VPHMG vulcanization and therefore provided the permanent antimicrobial performance for VMQ. 相似文献
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Thomas P. Klun Larry A. Wendling John W. C. Van Bogart Aida F. Robbins 《Journal of polymer science. Part A, Polymer chemistry》1987,25(1):87-109
The synthesis of new ionenes was accomplished by the reaction of novel diamines and dihalides. A new class of crosslinkable ionenes was made possible by the synthesis of tertiary diamines with acrylate functionality, generated ultimately from diepoxides and secondary amines. Other tertiary diamines were produced by endcapping of diols with tolylene diisocyanate, followed by reaction with N,N-dimethylethanolamine and also termination of living poly(tetrahydrofuran) polymer with dimethylamine. New dihalides were produced by the opening of diepoxides with ω-bromoacids. These diamines and dihalides underwent Menschutkin reactions providing novel ionenes for structure–property relationship studies. Correlations were drawn concerning amine nucleophilicity, dihalide nucleofugascity, and molecular weight. Stress–strain and thermal data reflected the effects of ionic domains and large flexible segments in the polymers. Also considered were the electrical conductivity, moisture–vapor transmission, and oxygen permeability of these materials. 相似文献
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Silicone polymers, due to their high lubricity and good spreading properties, are widely used in industrial applications. Being insoluble in water and most hydrocarbons, a common mode of delivering silicones is in the form of emulsions. To stabilize silicones in the emulsion form more efficiently, it is useful to understand the mechanism of emulsion stabilization. Two different mechanisms of emulsion stabilization have been proposed in the past: film formation and precipitation (known as the Pickering mechanism). These two mechanisms are different, and there is a need to further investigate this issue. The aim of the present work was to investigate the mechanism of stabilizing silicone emulsions and to propose a generalized behavior. Several experiments including the measurement of Langmuir isotherms, rheology experiments, phase diagram studies, and microscopy experiments were conducted. All of the above techniques indicated that the functional groups interact strongly with the water phase. The emulsions were found to be stable only if the emulsifiers were soluble in silicone oil or the water phase, and the stability decreased as the emulsifier precipitated. In most cases tested here, the emulsifiers were not observed to precipitate as reported earlier for the Pickering mechanism, and the emulsion stabilization followed film formation. These results should help to predict emulsion stabilization for unknown systems. 相似文献
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Mehta SC Somasundaran P Maldarelli C Kulkarni R 《Langmuir : the ACS journal of surfaces and colloids》2006,22(23):9566-9571
Organic/inorganic hybrid silicone polymers are increasingly used in cosmetics, inks and paints, and fabric care applications owing to their special Si-O bond characteristics. Because of the presence of organic as well as inorganic groups, they show the properties of both, and the presence of hydrophobic as well as hydrophilic character makes them behave like a hybrid polymer. Though they are widely used, the utilization of hydrophilically modified silicones on a large scale has mainly been empirical due to lack of fundamental knowledge about variation in their properties with systematic change in their structure. The choice of moieties for hydrophilic modification of silicones in most of the earlier works has been nonionic based on ethylene oxide and propylene oxide groups, however, very little is known about their ionic counterparts. The current work focuses on understanding the behavior of functionally grafted silicone polymers with respect to the variation in the hydrophilic part of the grafting chain. Hydrophilically grafted silicone polymers form monolayers at the air-water interface, which are stabilized by interactions of functional groups with water. The present work examined the effects of functional group modifications on the conformational behavior of chains at the interface. It was observed that the shape of the chain depends on the available area at the interface (or surface pressure), and there are conformational changes with an increase in the number of molecules per unit area. While a poly(dimethylsiloxanes) (PDMS) chain may undergo stretched to helix transition as predicted earlier, this may not be the case for hydrophilically grafted chains. On the basis of the shape of the surface pressure-area isotherm and correlation with the scaling theory, a gradation in hydrophilicity of functional groups and hence modified silicone chains at the air-water interface is predicted. 相似文献
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An orchid-like polyaniline (PANI) structures was synthesized by initialing the polymerization at 80 °C and growing at 25 °C using ethanol and water as co-solvent in the presence of toluene-p-sulfonic acid (p-TSA) as the dopant. The "flowers" are consisted of 8-14 pieces of "petals" with 5-8 μm in length. By adjusting the molar ratio of p-TSA/aniline, the cooling rate and the component of the solvent, flake-like and peony-like morphology can also be obtained. The formation mechanism of the orchid-like structure is proposed. 相似文献
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The ability of conjugated polymers to function as electronic materials is dependent on the efficient transport of excitons along the polymer chain. Generally, the photophysics of the chromophore monomer dictate the excited state behavior of the corresponding conjugated polymers. Different molecular structures are examined to study the role of excited state lifetimes and molecular conformations on energy transfer. The incorporation of rigid, three‐dimensional scaffolds, such as iptycenes and cyclophanes, can encourage an oblique packing of the chromophore units of a conjugated polymer, thus allowing the formation of electronically‐coupled aggregates that retain high quantum yields of emission. Rigid iptycene scaffolds also act as excellent structural directors that encourage complete solvation of PPEs in a liquid crystal (LC) solvent. LC‐PPE mixtures display both an enhanced conformational alignment of polymer chains and extended effective conjugation lengths relative to isotropic solutions, which leads to enhanced energy transfer. Facile exciton migration in poly(p‐phenylene ethynylene)s (PPEs) allows energy absorbed over large areas to be funneled into traps created by the binding of analytes, resulting in signal amplification in sensory devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
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In this paper the effect of the inclusion of two different thermotropic liquid crystal polymers (TLCP) on the processing of a polyetherimide (ULTEM 1000) is studied. 相似文献
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Owing to enthalpy relaxation, values of the glass transition temperature (Tg) for partially reacted polymers may depend on the thermal history of samples and the heating rate used for measurements. Use of theoretical relations between Tg and the extent of reaction (x) of a thermoset must take this fact into account. The original DiBenedetto equation has been reevaluated as a convenient constitutive equation for expressing Tg versus x. An extension of Couchman's approach for the expression of the compositional variation of Tg enabled us to derive the same functionality as given by the DiBenedetto equation. Thus, the DiBenedetto equation may be regarded as based on entropic considerations applied to a model of the thermosetting polymer consisting of a random mixture of a fully reacted network with the initial monomers in an amount which depends on the particular conversion level. These two equations have been applied with success to different diepoxy-diamine copolymers. 相似文献
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Blends of isotactic polypropylene and polyethylene or polyamides often display highly unusual crystalline morphologies in which the chain axes of the helical and linear polymers are at large angles to each other. These crystalline morphologies are explained on the basis of a specific epitaxial relationship that rests on the existence, in the (010) plane of iPP, of rows of methyl groups nearly 5-Å apart. The structural basis of all the observed morphologies is the parallel alignment of the aliphatic segments of the PE or polyamides and of the iPP methyl rows (or vice versa) and matching of the near 5-Å distances between PE or PA chains and iPP methyl rows. The implications of this unusual epitaxial relationship with respect to the apparent “universality” of polymer nucleating agents are examined. 相似文献
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<正>The hydrophilicity of silicone hydrogels used as soft corneal contact lens plays an important role in wearing comfort.In order to enhance hydrophilicity and protein resistance,silicone hydrogel membranes were modified by atmospheric pressure glow discharge plasma(APGDP) induced surface graft polymerization of N-vinyl pyrrolidone(NVP) and poly(oligoethylene glycol methyl ether methacrylate)(PEGMA) in this paper.XPS analysis demonstrated the success of graft polymerization of NVP and PEGMA onto the surface of silicone hydrogel membranes.The hydrophilicity of silicone hydrogels was characterized by the measurement of water contact angle(WCA).The result showed that NVP grafted silicone hydrogel has the WCA of about 68°and PEGMA grafted silicone hydrogel has the lowest WCA of about 62°,while the pristine silicone hydrogel is hydrophobic with the WCA of about 103°.Protein resistance of silicone hydrogels was investigated by the method of bicinchoninic acid assay using bovine serum albumin(BSA) as a model.It's found that the grafted silicone hydrogel has a significant improvement of protein resistance,and PEGMA grafting is more efficient for the reduction of protein adsorption than NVP grafting.The silicone hydrogel membranes grafted with NVP and PEGMA are good candidates of soft corneal contact lenses. 相似文献
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The feasibility of polymeric phases based on a silicone polymer backbone as pseudostationary phases for electrokinetic chromatography has been investigated. Silicone phases were studied because of the range of chemistries that could be developed based on these backbones, and because successful development of silicone phases would make it possible to employ much of the stationary phase chemistry developed in the past thirty years. Three silicone polymer structures have been investigated, but only one had sufficient aqueous solubility to permit application in electrokinetic chromatography. This phase was characterized by a variety of methods and was shown to be a mixture of partially hydrolyzed poly(bis-(3-cyanopropyl) siloxanes. When employed as a pseudostationary phase, this material provided selective and efficient separations. The electrophoretic mobility of the silicone polymer is greater than that of sodium dodecyl sulfate (SDS) micelles and poly(sodium 10-undecenylsulfate), providing an extended migration time range. A striking characteristic of the polymer is that the electrophoretic mobility is greater than typical electroosmotic mobilities. The chemical selectivity of the phase is significantly different from that of SDS micelles or poly(sodium 10-undecenylsulfate). The silicone phase is a more cohesive, basic and polar phase than SDS micelles. In buffers modified with a high concentration of organic solvents, the chromatographic properties of the silicone polymer are inferior to those of the poly(sodium 10-undecenylsulfate). The greatest limitation of silicone polymers for this application appears to be limited aqueous solubility, which will make it difficult to realize a family of such polymers with different chemical selectivities. 相似文献
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R. M. Gohil 《Colloid and polymer science》1992,270(2):128-133
A new approach for achieving a highly dimensionally stable film of semi-crystalline polymers via blending is demonstrated. To illustrate this approach, a model system, polyethylene-polypropylene is investigated using TEM, TMA, DSC, and DMA. It is shown that epitaxial growth in polymer blends and laminates can induce a cross-hatch morphology which eliminates or reduces the contribution of an oriented amorphous phase. This ultimately leads to greater dimensional stability and synergism in mechanical properties as well. The presence of an appropriate low-melting component can also be used to reduce shrinkage. 相似文献
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The solubility of carbon dioxide, methane, and propane in poly(dimethyl silmethylene) [(CH3)2SiCH2]x and poly(tetramethyl silhexylene siloxane) [(CH3)2Si (CH2)6Si (CH3)2O]x was measured in the temperature range from 10.0 to 55.0°C and at elevated pressures. The present results are compared with similar measurements made with other silicone polymers. At a given temperature and pressure, the solubility of the above three gases is highest in poly(dimethyl siloxane) (Me2SiO)x. The gas solubility is decreased by either backbone-chain or side-chain substitutions of functional groups in (Me2SiO)x which increase the stiffness of the polymer chains and decrease the specific or fractional free volume of the polymers. It is conjectured that a decrease in the free volume of silicone polymers has a greater effect in decreasing the gas solubility than differences in gas/polymer interactions [with the exception of specific interactions (e.g., between CO2 and polar groups in the polymer)]. © 1993 John Wiley & Sons, Inc. 相似文献
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The solubility of methane, carbon dioxide, and propane in five silicone polymers was measured at 10.0, 35.0 and 55.0°C and at pressures up to 26 atm. The polymers were poly(dimethyl siloxane), poly(methyl propyl siloxane), poly(methyl octyl siloxane), poly(trifluoropropyl methyl siloxane), and poly(phenyl methyl siloxane). At a given temperature and pressure, the solubility of the penetrant gases decreases with increasing bulkiness of the polymer side chains, and with decreasing critical temperature of the penetrant. The solubility of carbon dioxide in poly(trifluoropropyl methyl siloxane) appears to be anomalously high, possibly because of specific penetrant/polymer interactions. The temperature and pressure dependence of the solubility coefficients for the penetrant/polymer systems studied are described, and different methods of correlating these coefficients are compared. 相似文献
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Exact expressions are derived for the spinodal, critical conditions, and separation factor of a ternary solution consisting of a pure solvent and two monodisperse homologous polymers in which the Flory-Huggins interaction parameter χ depends separately on the concentrations of the polymer components. The results allow one to see the difference from previous expressions obtained with χ depending on the total concentration of the polymer, and are expected to be useful for experimental determination of the Gibbs free energy of ternary solutions. 相似文献