Home  About us  Contact
 

Improved Thermal (improved + thermal)

Distribution by Scientific Domains
Polymers and Materials Science75%

Terms modified by Improved Thermal

  • improved thermal stability
    		•

    Selected Abstracts

    Improved Chiral Olefin Metathesis Catalysts: Increasing the Thermal and Solution Stability via Modification of a C1 -Symmetrical N-Heterocyclic Carbene Ligand

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009
    Jolaine Savoie
    Abstract Four new ruthenium-based olefin metathesis catalysts that possess an N-heterocyclic carbene (NHC) ligand with benzyl (Bn) or or n -propyl (n -Pr) N-alkyl groups have been prepared. The synthetic routes developed for the synthesis of the required dihydroimidazolium salts are general. Catalysts bearing larger NHC ligands with larger N-alkyl groups displayed improved thermal and solution state stability up to 80,°C. The reactivity of the new catalysts in ring-closing metathesis is directly related to the increased steric bulk of the NHC ligand. The new catalysts have been evaluated in desymmetrization reactions and the nature of the N-alkyl group of the NHC ligands has been shown to have an important effect on the observed enantioselectivities. [source]

    Effect of hindered piperidine light stabilizer molecular structure and UV absorber addition on the oxidation of HDPE.

    JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2004
    Part 2: Mechanistic aspects, electron spin resonance spectroscopy study, molecular modeling
    The first in this series of papers explored the effect of the structural characteristics of 2,2,6,6-tetramethylpiperidine-based hindered amine light stabilizers (HALS) on the thermal and photostabilization of high-density polyethylene. In the second part, the energies (stabilities) of the nitroxyl radicals and various intermediate species have been predicted using AccuModel® and related to stabilization performance and electron spin resonance (ESR) spectral data. Nitroxyl radicals with low predicted stability generally afforded improved thermal and photostabilization. ESR spectra were used to obtain values of nitroxyl radical concentration ([>NO·]) and g -factor as a function of pre-aging time for combinations of pre-aged HDPE and >NH HALS. Demethylation reactions of > N-methyl HALS resulted in uselessly weak ESR spectra. The HALS that afforded poor thermal oxidative stabilization gave rise to pronounced minima in [>NO·] that coincided with a maximum in hydroperoxide concentration. The g -factor values indicated that a predominant nitroxyl canonical form generally promoted superior thermal oxidative stabilization, whereas a predominance of the dipolar N·+O, form promoted superior photo-oxidative stabilization. These trends may be related to greater radical-scavenging and peroxide-trapping effects, respectively. Molecular modeling and ESR spectra can therefore provide valuable insight into the effectiveness of HALS and stabilization mechanisms. J. Vinyl Addit. Technol. 10:159,167, 2004. © 2004 Society of Plastics Engineers. [source]

    Polyamide-12/Functionalized Carbon Nanofiber Composites: Evaluation of Thermal and Mechanical Properties

    MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2010
    Ricardo Chávez-Medellín
    Abstract This work aims at improving the interfacial bonding between polyamide-12 and CNFs. CNFs were oxidized and dispersed in polyamide-12 giving rise to polymer nanocomposites. The oxidation caused an increase in the specific surface area and structural defects of the fibers, as indicated by surface area and Fourier-transform Raman spectroscopy. The nanocomposites exhibited improved thermal and thermo-oxidative stabilities. The oxidized nanofibers had marginal effect on the crystallinity and crystallization of the polyamide-12. An over-proportional enhancement of stiffness due to the fibers could be achieved. In spite of these improvements the fiber/polymer adhesion should be further improved. [source]

    Preparation and properties investigation of PMMA/silica composites derived from silicic acid

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2009
    H. P. Fu
    Abstract Hybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6,M HCl. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright © 2008 John Wiley & Sons, Ltd. [source]