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Lower Thermal Stability (lower + thermal_stability)

Distribution by Scientific Domains

Polymers and Materials Science	80%

Selected Abstracts

Structure,property correlations of sulfonated polyimides.

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2004

Abstract 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]

Hyperbranched polymers from propargyloxysilanes: New types of acetylenic resins

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2001
Yingxin Xiao
Abstract New hyperbranched polymers (1P,3P) from propargyloxysilanes (1,3) are described. The propargyloxysilanes were prepared from readily available reagents in 53,61% yields. The polymerizations were clean, one-pot hydrosilylation processes catalyzed by Pt/C that were typically complete within 3 h. The polymers contained pendant acetylenic groups that underwent thermally induced crosslinking reactions. Heating the polymers to 1300 °C in flowing nitrogen resulted in weight losses ranging from 33 to 66%. Methyl substitution resulted in lower thermal stability. Further modification of the polymers was demonstrated by the reaction of 1P and 2P with phenylethynyldimethylsilane in the presence of a Pt catalyst. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3383,3391, 2001 [source]

Magnetic study of Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb)

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006

Abstract A family of the Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb) produced in an argon atmosphere as amorphous ribbons with 0.025 mm thickness are investigated up to 1200 K. The partial replacement of Fe by Co with optimal Fe0.5Co0.5 ratio increases the Curie temperature of the amorphous phase and the magnetic moment per formula unit. The early stages of crystallization can be observed by magnetization measurements. Alloys subjected to the first controlled crystallization stage are built of bcc-(Fe,Co) nanocrystals that are homegeneously embedded in the amorphous matrix. Mean grain sizes are about 11 nm. These two-phase alloys exhibit good soft magnetic properties with the relatively low coercive fields up to 50 A/m. Hafnium and hafnium/zirconium mixture are found to be the best inhibitors of the nanograin growth resulting in the best soft magnetic parameters. Alloys with niobium exhibit lower thermal stability and higher coercive fields. The correlation between the structure evolution and the magnetic properties is analysed and discussed. Conditions for optimum heat treatment are also determined. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Conducting nanocomposites of polyacrylamide with acetylene black and polyaniline

POLYMER COMPOSITES, Issue 4 2009
Pramod Kumar Verma
A conducting nanocomposite of polyacrylamide (PAA) with acetylene black was prepared via Na2AsO3 -K2CrO4 redox initiated polymerization of acrylamide in water containing a suspension of acetylene black. FTIR analyses confirmed the presence of PAA in the nanocomposites. The composite possessed lower thermal stability than AB and exhibited three stages of decomposition upto 430°C. DSC thermogram revealed three endotherms due to minor thermal degradation (at ,100°C), melting and decomposition (at ,230°C) and major decomposition (at ,430°C). TEM analyses indicated the formation of globular composite particles with sizes in 30,70 nm range. In contrast to the very low conductivity of the base polymer the composite showed a dramatic increase in conductivity (0.19,6.0 S/cm) depending upon AB loading. Log (conductivity) ,1/T plot showed a change in slope at ,127°C indicating the manifestation of an intrinsic conductivity region and an impurity conductivity region. The activation energy for conduction as estimated from the slope of region I was 0.008 eV/mol. The C,V plot was linear showing a metallic behavior. For comparison in conductivity PAA-polyaniline composite was also prepared which however displayed much lower conductivity values. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]

Completely discontinuous organic/ inorganic hybrid nanocomposites by self-curing of nanobuilding blocks constructed from reactions of [HMe2SiOSiO1.5]8 with vinylcyclohexene

POLYMER INTERNATIONAL, Issue 11 2007
Norihiro Takamura
Abstract The reaction of 4-vinyl-1-cylcohexene with [HMe2SiOSiO1.5]8 provides tetra- and octa-2-cyclohexenylethyloctasilsesquioxanes. The tetrabifunctional [cyclohexenylethylMe2SiOSiO1.5]4 -[HMe2SiOSiO1.5]4 (average degree of functionalization) melts near 80 °C and can be cast and then cured (by thermal hydrosilylation) into transparent nanocomposite shapes. These materials, while not nanoporous, offer dielectric constants of 2.8,2.9 at 100 kHz to 3 MHz, and are air stable to temperatures , 400 °C. The resulting materials appear (by X-ray diffraction) to be partially ordered after curing. The octafunctional material also melts at low temperatures (ca 120 °C) and can be copolymerized with hydridosiloxanes to give similar materials with lower thermal stability. The synthesis and characterization of the starting materials is described, as well as thermal curing studies and properties characterization of the resultant nanocomposites. Copyright © 2007 Society of Chemical Industry [source]