High molecular weight polymethylene. Part 1.—The kinetics of the copper salt catalyzed decomposition of diazomethane

1954 ◽  
Vol 50 (0) ◽  
pp. 934-941 ◽  
Author(s):  
C. E. H. Bawn ◽  
T. B. Rhodes
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Copper Salt ◽  
Kinetics Of

scholarly journals Thermal Degradation Kinetics and Modeling Study of Ultra High Molecular Weight Polyethylene (UHMWP)/Graphene Nanocomposite

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1597
Author(s):  
Iman Jafari ◽  
Mohamadreza Shakiba ◽  
Fatemeh Khosravi ◽  
Seeram Ramakrishna ◽  
Ehsan Abasi ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Molecular Weight ◽  
Thermal Degradation ◽  
High Molecular Weight ◽  
Degradation Kinetics ◽  
Graphene Nanosheets ◽  
Thermal Degradation Kinetics ◽  
Graphene Nanocomposites ◽  
Kinetics Of ◽  
Ultra High Molecular Weight

The incorporation of nanofillers such as graphene into polymers has shown significant improvements in mechanical characteristics, thermal stability, and conductivity of resulting polymeric nanocomposites. To this aim, the influence of incorporation of graphene nanosheets into ultra-high molecular weight polyethylene (UHMWPE) on the thermal behavior and degradation kinetics of UHMWPE/graphene nanocomposites was investigated. Scanning electron microscopy (SEM) analysis revealed that graphene nanosheets were uniformly spread throughout the UHMWPE’s molecular chains. X-Ray Diffraction (XRD) data posited that the morphology of dispersed graphene sheets in UHMWPE was exfoliated. Non-isothermal differential scanning calorimetry (DSC) studies identified a more pronounced increase in melting temperatures and latent heat of fusions in nanocomposites compared to UHMWPE at lower concentrations of graphene. Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) revealed that UHMWPE’s thermal stability has been improved via incorporating graphene nanosheets. Further, degradation kinetics of neat polymer and nanocomposites have been modeled using equations such as Friedman, Ozawa–Flynn–Wall (OFW), Kissinger, and Augis and Bennett’s. The "Model-Fitting Method” showed that the auto-catalytic nth-order mechanism provided a highly consistent and appropriate fit to describe the degradation mechanism of UHMWPE and its graphene nanocomposites. In addition, the calculated activation energy (Ea) of thermal degradation was enhanced by an increase in graphene concentration up to 2.1 wt.%, followed by a decrease in higher graphene content.

Degradation kinetics of high molecular weight poly(L-lactide) microspheres and release mechanism of lipid:DNA complexes

2004 ◽  
Vol 93 (10) ◽  
pp. 2573-2584 ◽  
Author(s):  
Mayank M. Patel ◽  
Michelle G. Zeles ◽  
Mark C. Manning ◽  
Theodore W. Randolph ◽  
Thomas J. Anchordoquy
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Degradation Kinetics ◽  
Release Mechanism ◽  
Kinetics Of ◽  
High Molecular Weight Poly

KINETIC EFFECTS OF HIGH MOLECULAR WEIGHT KININOGEN AND ZINC ON CONTACT ACTIVATION

1987 ◽  
Author(s):  
J D Shore ◽  
D E Day ◽  
S T Olson
Keyword(s):  
Molecular Weight ◽  
Ionic Strength ◽  
High Molecular Weight ◽  
Proper Function ◽  
Factor Xii ◽  
High Molecular Weight Kininogen ◽  
Contact Activation ◽  
Kinetic Effects ◽  
Activation Rates ◽  
Kinetics Of

Previous work in our laboratory showed that Zn2+ enhanced the rate of kallikrein generation by dextran sulfate (DxSO4) in dialyzed normal plasma, but not in Fitzgerald or Hageman prismas. This could be partially explained by a marked effect of Zn2+ on factor XII autoactivation, and our present work involves zinc effects on other reactions of contact activation. At physiological ionic strength (0.15 μ), the kcat/Km for Xlla activation of prekallikrein (PK) was 0.62 μM™1 s™1 which was increased to 4.35 μM™1 s™1 by the presence of 25μg/ml DxSO4. High molecular weight kininogen (HMK) at 40 nM further increased this to 10.8 μM™1 s™1 , and 5 ¼M Zn2+ had no effect. To determine whether these cofactors promote a surface-dependent activation of PK by XIIa under conditions which weaken the protein-surface interactions, the kinetics were examined at 0.3μ. At this ionic strength, kcat/Km was 0.18 μM™1 s™1 and was unchanged by 25μg/ml DxSO4. This was increased to .805 μM™1 s™1 by 150 nM HMK and further increased 10-fold to 8.35 μM™1 s™1 by 10 μM™1 Zn2+ . Qualitative results were obtained at 0.3 μ for the other reciprocal reaction, XII activation by kallikrein (K). To observe XII activation within 2 hours, both 10 μM Zn2+ and 25 μM HMK were essential, indicating that these cofactors have a very large enhancing effect on the kinetics of this reaction. Chromatography of HMWK on DxSO4-agarose ^ljiowed elution of the protein at 0.42 M NaCl in the absence of Zn2+ ,but at 0.88M in its presence, providing evidence that Zn+ markedly increases the affinity of HMK for DxSO4. Our results are consistent with the increased activation rates observed in the presence of Zn2+ and HMK due to enhanced binding affinity of the reacting proteins to surfaces. This is likely to be essential for proper function of the contact system in blood, where many other proteins compete for surface. Supported by USPHS grant HL-25670

Metabolism of high molecular weight, polydisperse, rapidly labeled nuclear RNA in rat liver

1968 ◽  
Vol 46 (12) ◽  
pp. 1497-1505 ◽  
Author(s):  
Maurice Brossard ◽  
Louis Nicole
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Rat Liver ◽  
Ribosomal Rna ◽  
Base Composition ◽  
Orotic Acid ◽  
Chromosomal Origin ◽  
Base Analysis ◽  
Nuclear Rna ◽  
Kinetics Of

Studies of the metabolism of rat liver RNA showed the existence of two species of rapidly labeled nuclear RNA: a 45 S preribosomal type of nucleolar origin, and a 6–50 S polydisperse RNA of chromosomal origin. The kinetics of labeling with orotic acid-14C and the nature of the latter RNA have been investigated. The following findings are reported, (1) This RNA is composed of at least four main classes of RNA having sedimentation coefficients of approximately 45, 35, 24, and 18 S. (2) Except for the 18 S class which seems to be an end product, the three other classes have a rapid turnover and do not appear to leave the nucleus. (3) Base analysis after 32P incorporation indicates that these four classes of RNA have a similar base composition with a G+C/A + U ratio in the range of 0.98–1.07, which resembles DNA more closely than ribosomal RNA. (4) The 6–50 S polydisperse RNA has a different metabolism than that of the 45 S preribosomal type and there is no precursor-to-product relationship between these two species of RNA.

scholarly journals Characterization of uterine heterogeneous nuclear ribonucleic acid and the effect of oestradiol-17β on its synthesis

1978 ◽  
Vol 172 (3) ◽  
pp. 587-593 ◽  
Author(s):  
S Aziz ◽  
J T Knowler
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Early Response ◽  
Oestrogen Treatment ◽  
Size Profile ◽  
Immature Rats ◽  
Nuclear Rna ◽  
Kinetics Of ◽  
Molecular Weight Fractions

An early response to the administration of oestradiol-17 beta to immature rats is a dramatic stimulation in the synthesis of uterine hnRNA (heterogenous nuclear RNA). High-molecular-weight fractions of the hnRNA were purified and subfractionated on poly(U)-Sepharose into fractions that differed in their poly(A) content and their size profile on polyacrylamide gels. Oestrogen treatment of the rats stimulated the synthesis of all three fractions of high-molecular-weight hnRNA, but the kinetics of synthesis, degree of stimulation and size distribution of the newly synthesize RNA differed in each fraction.

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