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排序方式: 共有86条查询结果,搜索用时 103 毫秒
1.
Cyclomatrix phosphazene–triazine network polymers were synthesized by co‐curing a blend of tris(2‐allylphenoxy), triphenoxy cyclotriphosphazene (TAP), and tris(2‐allylphenoxy) s‐triazine (TAT) with bis(4‐maleimido phenyl) methane (BMM). The co‐curing of the three‐component resin was investigated by dynamic mechanical analysis using rheometry. The cure kinetics of the Diels–Alder step was studied by examining the evolution of the rheological parameters, such as storage modulus (G′), loss modulus (G″), and complex viscosity (η*), for resins of varying compositions at different temperatures. The curing conformed to an overall second‐order phenomenological equation, taking into account a self‐acceleration effect. The kinetic parameters were evaluated by multiple‐regression analysis. The absence of a definite trend in the cure process with blend composition ratio was attributed to the occurrence of a multitude of competitive reactions whose relative rates depend on the reactant ratio and the concentration of the products formed from the initial phase of reaction. The cure was accelerated by temperature for a given composition, whereas the self‐acceleration became less prominent at higher temperature. Gelation was accelerated by temperature. The gel conversion decreased with increase in maleimide concentration and, for a given composition, it was independent of the cure temperature. The activation energy for the initial reaction and the crosslinking process were estimated for a composition with a maleimide‐to‐allyl ratio of 2 : 1. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 908–914, 2003 相似文献
2.
Renjith Devasia CP Reghunadhan Nair P Sivadasan KN Ninan 《Polymer International》2005,54(8):1110-1118
Polyacrylonitrile terpolymers of various compositions consisting of acrylonitrile (AN), itaconic acid (IA) and methyl acrylate (MA) were synthesized by solution polymerization in dimethylsulfoxide. Increase in concentration of either IA or MA retarded the overall polymerization rate and the polymer molecular weight. The system consisting of AN + MA and varying IA concentration was more prone to retardation in comparison with the system composed of AN + IA with variable MA concentration. The retardation factors were quantified. Minor quantities of MA boost the reactivity of IA in the terpolymer system. The terpolymer was richer in MA vis‐à‐vis the feed. The thermal characteristics of the terpolymer were examined as a function of its composition. In contrast to the copolymer of AN and IA requiring 1–1.5 mol% IA, the terpolymer required an IA content of approximately 2.5 mol% for optimum thermal stability. The polymer with 90 mol% AN, 2.5 mol% IA and 7.5 mol% MA exhibited reasonably good char‐forming characteristics and thermal stability. The overall crystallinity and crystallite size of the polymers were found to decrease on incorporation of the comonomers. The ‘aromatization index’ of the copolymer increased with the temperature of pyrolysis through re‐organization of the tetrahydropyridine ladder structure. Copyright © 2005 Society of Chemical Industry 相似文献
3.
Tert‐butyl hydroquinone–based poly(cyanoarylene ether) (PENT) was synthesized by the nucleophilic aromatic substitution reaction of 2,6‐dichlorobenzonitrile with tert‐butyl hydroquinone using N‐methyl‐2‐pyrrolidone (NMP) as solvent in the presence of anhydrous potassium carbonate in a nitrogen atmosphere at 200°C. PENT‐toughened diglycidyl ether of bisphenol A epoxy resin (DGEBA) was developed using 4,4′‐diaminodiphenyl sulfone (DDS) as the curing agent. Scanning electron micrographs revealed that all blends had a two‐phase morphology. The morphology changed from dispersed PENT to a cocontinuous structure with an increase in PENT content in the blends from 5 to 15 phr. The viscoelastic properties of the blends were investigated using dynamic mechanical thermal analysis. The storage modulus of the blends was less than that of the unmodified resin, whereas the loss modulus of the blends was higher than that of the neat epoxy. The tensile strength of the blends improved slightly, whereas flexural strength remained the same as that of the unmodified resin. Fracture toughness was found to increase with an increase in PENT content in the blends. Toughening mechanisms like local plastic deformation of the matrix, crack path deflection, crack pinning, ductile tearing of thermoplastic, and particle bridging were evident from the scanning electron micrographs of failed specimens from the fracture toughness measurements. The thermal stability of the blends were comparable to that of the neat resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3536–3544, 2006 相似文献
4.
PT Ninan B Knight L Kirk BO Rothbaum J Kelsey CB Nemeroff 《Canadian Metallurgical Quarterly》1998,34(2):221-224
Vibrio vulnificus, a particularly virulent halophilic vibrio, has been isolated from the blood and skin necrotic lesion of a hemodialyzed patient with sepsis. The patient has had exposure of the skin to seawater. Various chronic conditions including renal failure have a great risk for developing septicemia due to V vulnificus. It is necessary to inform persons with liver diseases or immunocompromising conditions of hazards associated with the consumption of undercooked seafood and seawater exposure. 相似文献
5.
6.
Bibin John C. P. Reghunadhan Nair K. Ambika Devi K. N. Ninan 《Journal of Materials Science》2007,42(14):5398-5405
Syntactic foam composites of cyanate ester with varying volume fractions of resin and glass microballoon were processed and
evaluated for tensile, flexural and compressive properties. The effect of nature and volume fraction of microballoon on the
mechanical properties was studied. The mechanical properties showed a gradual decrease in strength with increase in volume
fraction of microballoon. The specific strength values also manifested a similar order. A similar behaviour was observed for
syntactic foams with microballoons of varying true density. The properties increased proportional to the strength of the microballoon
in resin-rich systems implying a strong microballoon-resin interface, corroborated by Scanning Electron Microscopy studies.
The compressive modulus showed a decreasing trend with enhanced microballoon loading. 相似文献
7.
P. V. Prabhakaran K. J. Sreejith B. Swaminathan S. Packirisamy K. N. Ninan 《Journal of Materials Science》2009,44(2):528-533
Phenol-furfuraldehyde (PFu) resin synthesized in our laboratory was characterized for its thermal properties and mixed with
elemental silicon and the mixture was evaluated as precursor for SiC ceramics. The mix on sintering at 1,500 °C gave nano-SiC
powder. The sintering experiment carried out in flowing argon has also resulted in the formation of SiC wires/fibers having
diameter in nano to sub-micron range. 相似文献
8.
K. N. Ninan V. P. Balagangadharan K. Ambikadevi K. B. Catherine 《Polymer International》1993,31(3):255-260
A novel approach is proposed for estimating the average molecular weight between crosslinks (M?c) from the functionality distribution of hydroxyl-terminated polybutadiene ( HTPB ). The functionality distribution of four free-radically polymerised HTPB prepolymers of varying hydroxyl content and molecular weight was determined by a combination of preparative and analytical gel permeation chromatography. The gumstock properties of the samples cured with stoichiometric amounts of toluene diisocyanate were not correlatable with the relative amounts of difunctional chain extender and multifunctional crosslinker present, unlike the case of HTPB with similar hydroxyl content and molecular weight. However, the mechanical properties and sol content could be correlated with the average molecular weight between crosslink sites, M?c, of the cured polymer. The M?c values derived by our method compare well with those of classical methods, and the observed differences are attributed to segmental entanglement. These M?c values give consistently good correlation with all the gumstock properties, confirming the validity of our approach and the soundness of the techniques developed for the determination of the functionality distribution of HTPB . 相似文献
9.
Akanksha Saxena R. Sadhana V. Lakshmana Rao P. V. Ravindran K. N. Ninan 《应用聚合物科学杂志》2006,99(4):1303-1309
Poly ether nitrile and poly ether nitrile sulfone copolymers with pendant methyl groups were prepared by the nucleophilic substitution reaction of 2,6′‐dichlorobenzonitrile with methyl hydroquinone and with varying mole proportions of methyl hydroquinone and 4,4′dihydroxydiphenylsulfone using N‐methyl pyrrolidone as solvent in the presence of anhydrous K2CO3. The polymers were characterized by different physicochemical techniques. Copolymer composition was determined using FTIR technique. Thermogravimetric data reveals that all the polymers were stable up to 420°C with a char yield above 40% at 900°C in N2 atmosphere. The glass transition temperature was found to increase and the activation energy and inherent viscosities were found to decrease with increase in concentration of the 4,4′‐dihydroxydiphenylsulfone units in the polymer. Trimerization reactions are found to be favorable with increase in concentration of methyl hydroquinone units in the polymer. Crystallinity of the polymer was also studied using wide angle X‐ray diffraction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1303–1309, 2006 相似文献
10.
A maleimide‐functional phenolic resin was reactively blended with an allyl‐functional novolac in varying proportions. The two polymers were coreacted by an addition mechanism through Alder‐ene and Wagner–Jauregg reactions to form a crosslinked network system. The cure characterization was done by differential scanning calorimetry and dynamic mechanical analysis. The system underwent a multistep curing process over a temperature range of 110–270°C. Although the cure profiles were independent of the composition, the presence of maleimide led to a reduced isothermal gel time of the blend. Increasing the allylphenol content decreased the crosslinking in the cured matrix, leading to enhanced toughness and improved resin‐dominant mechanical properties of the resultant silica laminate composites. Changing the reinforcement from silica to glass resulted in further amelioration of the resin‐reinforcement interaction, but the resin‐dominant properties of the composite remained unaltered. Increasing the maleimide content resulted in enhanced thermal stability. Integrating both the reactive groups in a single polymer and its curing led to enhanced thermal stability and Tg, but to decreased mechanical properties of the laminate composites. This can be attributed to a brittle matrix resulting from enhanced crosslinking facilitated by interaction of the reactive groups located on the polymer of an identical backbone structure. The cured polymers showed a Tg in the range of 170–190°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 737–749, 2001 相似文献