scholarly journals A Simplified Method for Formulation of Epoxy Resin Embedding Media

2006 ◽  
Vol 14 (5) ◽  
pp. 50-51 ◽  
Author(s):  
E. Ann Ellis
Keyword(s):  
Molecular Weight ◽  
Epoxy Resin ◽  
Molar Ratio ◽  
Molecular Weights ◽  
Molar Ratios ◽  
Low Viscosity ◽  
Simplified Method ◽  
Beam Stability ◽  
Embedding Medium

In a recent paper on the revised formulation of Spurr low viscosity embedding medium with ERL 4221 the importance of maintaining an appropriate anhydride:epoxide (A:E) ratio was discussed. By understanding a few simple concepts about epoxy resin formulations and setting up a formulation table it is possible to create new resin mixtures with good sectioning properties and other desirable properties such as decreased viscosity and increased beam stability.Before starting a formulation you need to know the molecular weight of the anhydride and the WPE (weight per epoxide equivalent) of the epoxy resin component. The molecular weights and WPEs are usually printed on the bottle or can be obtained from the vendor. An A:E ratio of 0.7:1.0 -1.0:1.0 is used for most biological specimens. Increasing the A:E ratio results in a harder block; decreasing the A:E ratio results in a softer block. Table 1 shows a basic formulation spreadsheet where the molecular weights of the anhydrides and the WPEs of the epoxy resin components can be entered. The A:E ratio is entered under the anhydride for the molar ratio and the molar ratios of the epoxy components are entered under the epoxy components. The calculations are done as shown in each column and row.

Synthesis and characterization of novel β-cyclodextrin cored poly(α-caprolactone)s by anionic ring opening polymerization

e-Polymers ◽  
2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Yingzhi Guo ◽  
Changjiang Yu ◽  
Zhongwei Gu
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Ring Opening ◽  
Monomer Conversion ◽  
Ring Opening Polymerization ◽  
Molar Ratio ◽  
Molecular Weights ◽  
Molar Ratios ◽  
Anionic Ring ◽  
Feed Molar Ratio

Abstract By anionic ring opening polymerization initiated by cyclodextrin oxyanions generated from NaH and β-cyclodextrin(β-CD), novel biodegradable β- CD cored star-shaped poly(ε-caprolactone)s (s-PCLs) were synthesized and then characterized by means of FTIR, GPC, 1H-NMR. The effects of different feed molar ratios of NaH and β-CD on arm number and on the molecular weight of s-PCLs, and the relationship between the polymerization time and monomer conversion were investigated. Moreover, the physical properties of linear PCL (l-PCL) and s- PCLs with similar molecular weights but different arm number were studied and compared by DSC, SEM and intrinsic viscosity measurement, respectively. It was found that the feed molar ratio of NaH and β-CD is an important factor which influences both the molecular weight and arm number. The melting points and intrinsic viscosities of s-PCLs with similar molecular weights were lower than that of l-PCL, and were found to decrease with increasing arm number. Both SEM and AFM showed that the surface morphology of s-PCL films was different from that of l-PCL. These results indicated that s-PCL with different arms and physical properties could be synthesized using just a β-CD core by adjusting the feed molar ratio of NaH and β-CD

scholarly journals Solutions to the Problem of Substitution of ERL 4221 for Vinyl Cyclohexene Dioxide in Spurr Low Viscosity Embedding Formulations

2006 ◽  
Vol 14 (4) ◽  
pp. 32-33 ◽  
Author(s):  
E. Ann Ellis
Keyword(s):  
Molecular Weight ◽  
Epoxy Resin ◽  
Succinic Anhydride ◽  
Original Formulation ◽  
Plant Materials ◽  
Low Viscosity ◽  
Direct Substitution ◽  
Embedding Medium

Spurr low viscosity embedding medium was introduced in 1969 and used vinyl cyclohexene dioxide (VCD or ERL 4206) as the low viscosity epoxy resin together with nonenyl succinic anhydride (NSA), the flexibilizer DER 736, and the accelerator dimethylaminoethanol (DMAE or S-1). This low viscosity formulation has been used extensively for embedding plant materials, microrganisms and other difficult specimens. Over the years numerous concerns about the toxicity and carcinogenicity of VCD have been raised. VCD (Fig. 1) was finally removed from the market in 2005 and replaced with ERL 4221 (Fig. 2), a cyclic epoxide with a higher molecular weight and higher viscosity. Vendors instructed that ERL 4221 be substituted for VCD at the same rates as used in the original Spurr formulation. This direct substitution resulted in a more viscous resin and blocks were extremely hard and brittle and lacked the sectioning qualities of the original formulation. Vendors then suggested modifications to the dehydration schedule and reductions in the amount of DMAE to improve the quality of the blocks.

Polymerization of n-butyl methylacrylate using bis(β- ketoamino)nickel(II)/MAO catalytic systems

e-Polymers ◽  
2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Xiaohui He ◽  
Yiwang Chen ◽  
Yongming Liu ◽  
Muqing Chen ◽  
Shuxian Yu ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Monomer Concentration ◽  
Polymerization Temperature ◽  
Moderate Activity ◽  
Polymerization Time ◽  
Catalytic Systems ◽  
Molecular Weights ◽  
Molar Ratios ◽  
Broad Molecular Weight Distribution ◽  
C Nmr

AbstractThe polymerizations of n-butyl methylacrylate (nBMA) were carried out using bis(β-ketoamino)nickel(II) complexes (Ni[CH3C(O)CHC(NR)CH3]2: R = phenyl, 1; R = naphthyl, 2) in combination with methylaluminoxane (MAO) in toluene. The effect of parameters such as polymerization temperature, Al/Ni molar ratios, polymerization time, and monomer concentration, on catalytic polymerization activity and polymer molecular weights, were examined in detail. Both of the nickel(II) catalytic systems exhibited moderate activity, and produced P(nBMA) with high molecular weight and relatively broad molecular weight distribution (Mw/Mn=2.0~3.0. The obtained polymer has been characterized by means of FTIR, 1H NMR, 13C NMR, DSC, and WAXD technique and was confirmed to be syndio-rich stereospecific P(nBMA).

scholarly journals Methylene-Bridged Tridentate Salicylaldiminato Binuclear Titanium Complexes as Copolymerization Catalysts for the Preparation of LLDPE through [Fe]/[Ti] Tandem Catalysis

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1114 ◽  
Author(s):  
Yani Luo ◽  
Jian Li ◽  
Derong Luo ◽  
Qingliang You ◽  
Zifeng Yang ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Temperature ◽  
Gel Permeation Chromatography ◽  
13C Nmr Spectroscopy ◽  
Molar Ratio ◽  
Tandem Catalysis ◽  
Titanium Complexes ◽  
Scanning Calorimetry ◽  
Molecular Weights ◽  
Branching Degree

A novel tandem catalysis system consisted of salicylaldiminato binuclear/mononuclear titanium and 2,6-bis(imino)pyridyl iron complexes was developed to catalyze ethylene in-situ copolymerization. Linear low-density polyethylene (LLDPE) with varying molecular weight and branching degree was successfully prepared with ethylene as the sole monomer feed. The polymerization conditions, including the reaction temperature, the Fi/Ti molar ratio, and the structures of bi- or mononuclear Ti complexes were found to greatly influence the catalytic performances and the properties of obtained polymers. The polymers were characterized by differential scanning calorimetry (DSC), high temperature gel permeation chromatography (GPC) and high temperature 13C NMR spectroscopy, and found to contain ethyl, butyl, as well as some longer branches. The binuclear titanium complexes demonstrated excellent catalytic activity (up to 8.95 × 106 g/molTi·h·atm) and showed a strong positive comonomer effect when combined with the bisiminopyridyl Fe complex. The branching degree can be tuned from 2.53 to 22.89/1000C by changing the reaction conditions or using different copolymerization pre-catalysts. The melting points, crystallinity and molecular weights of the products can also be modified accordingly. The binuclear complex Ti2L1 with methylthio sidearm showed higher capability for comonomer incorporation and produced polymers with higher branching degree and much higher molecular weight compared with the mononuclear analogue.

Synthesis and Properties of Biodegradable ABA Triblock Copolymers of Polylactide (A) and Polyethylene Glycol (B)

2006 ◽  
Vol 11-12 ◽  
pp. 469-472 ◽  
Author(s):  
Shu Xian Shi ◽  
Yu Zheng Xia ◽  
Xiao Yan Ma ◽  
Shu Ke Jiao ◽  
Xiao Yu Li
Keyword(s):  
Molecular Weight ◽  
Ethylene Glycol ◽  
Ring Opening ◽  
Average Molecular Weight ◽  
Analytical Techniques ◽  
Normal Pressure ◽  
Molar Ratio ◽  
Poly Ethylene Glycol ◽  
Molar Ratios ◽  
Poly Ethylene

The triblock ABA copolymers of poly (D,L-lactide)-b-poly (ethylene glycol)-b-poly (D,L-lactide) (PDLLA-PEG-PDLLA) were synthesized by bulk ring-opening polymerization in the presence of N2 under normal pressure, using the D,L-lactide (DLLA) as monomer, hydroxyl endgroups of poly(ethylene glycol) (PEG) as initiator and the stannous octoate as the catalyst. The resulting copolymers were characterized by various analytical techniques. Effects of molar ratios of lactide to PEG and the chain length of PEG on the viscosity-average molecular weight of the copolymers, the biodegradation behaviors and hydrophilicity of the copolymers were investigated in detail. The results showed that the viscosity-average molecular weight and the contact angle of the copolymers increased with the molar ratio of lactide to PEG, but water uptake and degradability decreased.

scholarly journals Biosynthesis of Novel Exopolymers byAureobasidium pullulans

1999 ◽  
Vol 65 (12) ◽  
pp. 5265-5271 ◽  
Author(s):  
Jin W. Lee ◽  
Walter G. Yeomans ◽  
Alfred L. Allen ◽  
Fang Deng ◽  
Richard A. Gross ◽  
...  
Keyword(s):  
Energy Source ◽  
Molecular Weight ◽  
Carbon Sources ◽  
Enzyme Hydrolysis ◽  
Molar Ratio ◽  
Glucose Content ◽  
Molar Ratios ◽  
Culture Time ◽  
New Family ◽  
Compositional Changes

ABSTRACT Aureobasidium pullulans ATCC 42023 was cultured under aerobic conditions with glucose, mannose, and glucose analogs as energy sources. The exopolymer extracts produced under these conditions were composed of glucose and mannose. The molar ratio of glucose to mannose in the exopolymer extract and the molecular weight of the exopolymer varied depending on the energy source and culture time. The glucose content of exopolymer extracts formed with glucose and mannose as the carbon sources was between 91 and 87%. The molecular weight decreased from 3.5 × 106 to 2.12 × 106 to 0.85 × 106 to 0.77 × 106 with culture time. As the culture time increased, the glucose content of the exopolymer extract formed with glucosamine decreased from 55 ± 3 to 29 ± 2 mol%, and the molecular weight increased from 2.73 × 106 to 4.86 × 106. There was no evidence that glucosamine was directly incorporated into exopolymers. The molar ratios of glucose to mannose in exopolymer extracts ranged from 87 ± 3:13 ± 3 to 28 ± 2:72 ± 2 and were affected by the energy source added. On the basis of the results of an enzyme hydrolysis analysis of the exopolymer extracts and the compositional changes observed, mannose (a repeating unit) was substituted for glucose, which gave rise to a new family of exopolymer analogs.

scholarly journals The structure and subunit composition of the particulate NADH-ubiquinone reductase of bovine heart mitochondria

1976 ◽  
Vol 154 (2) ◽  
pp. 295-305 ◽  
Author(s):  
C. I Ragan
Keyword(s):  
Molecular Weight ◽  
Complex I ◽  
Gradient Centrifugation ◽  
Sodium Dodecyl ◽  
Water Soluble ◽  
Heart Mitochondria ◽  
Molar Ratio ◽  
Polypeptide Composition ◽  
Molecular Weights ◽  
Bovine Heart

Preparations of NADH-ubiquinone reductase from bovine heart mitochondria (Complex I) were shown to contain at least 16 polypeptides by gel electrophoresis in the presence of sodium dodecyl sulphate. 2. High-molecular-weight soluble NADH dehydrogenase prepared from Triton X-100 extracts of submitochondrial particles [Baugh & King (1972) Biochem. Biophys. Res. Commun. 49, 1165-1173] was similar to Complex I in its polypeptide composition. 3. Solubilization of Complex I by phospholipase A treatment and subsequent sucrose-density-gradient centrifugation did not alter the polypeptide composition. 4. Lysophosphatidylcholine treatment of Complex I caused some selective solubilization of a polypeptide of mol.wt. 33000 previosuly postulated to be the transmembrane component of Complex I in the mitochondrial membrane [Ragan (1975) in Energy Transducing Membranes: Structure, Function and Reconstitution (Bennun, Bacila & Najjar, eds.), Junk, The Hague, in the press]. 5. Chaotropic resolution of Complex I caused solubilization of polypeptides of molecular weights 75000, 53000, 29000, 26000 and 15500 and traces of others in the 10000-20000-mol.wt.range. 6. The major components of the iron-protein fraction from chaotropic resolution had molecular weights of 75000, 53000 and 29000, whereas the flavoprotein contained polypeptides of molecular weights 53000 and 26000 in a 1:1 molar ratio. 7. Iodination of Complex I by lactoperoxidase indicated that the water-soluble polypeptides released by chaotropic resolution, in particular those of the flavoprotein fraction, were largely buried in the intact Complex. 8. The polypeptides of molecular weights 75000, 53000, 42000, 39000, 33000, 29000 and 26000 were present in 1:2:1:1:1:1:1 molar proportions. The two subunits of molecular weight 53000 are probably non-identical.

scholarly journals Properties of pig heart aconitase

1974 ◽  
Vol 143 (3) ◽  
pp. 717-722 ◽  
Author(s):  
Oscar Gawron ◽  
Mary C. Kennedy ◽  
Richard A. Rauner
Keyword(s):  
Molecular Weight ◽  
Electron Spin Resonance ◽  
Resonance Spectrum ◽  
Specific Activity ◽  
Thiol Group ◽  
Molar Ratio ◽  
Candida Lipolytica ◽  
Molar Ratios ◽  
Acid Titration ◽  
Spin Resonance

Comparison of pig heart aconitase (Kennedy et al., 1972) with yeast (Candida lipolytica) aconitase (Suzuki et al., 1973) reveals similarities in molecular weight and iron content but not in sulphide content. Comparison with the Mildvan & Villafranca (1971) pig heart aconitase preparation reveals differences in iron ligands, specific activity and other properties; these differences possibly arise from protein association as pig heart protein associates under a variety of conditions. The electron spin resonance spectrum, g 4.25, and the low molar relaxivity, 473m−1·s−1, of water H+ suggest the presence of high-spin Fe(III) unco-ordinated to water in the enzyme. The iron chromophore on acid titration at 320nm gives a curve with an inflexion at pH4.2. Ten of 16 expected thiol equivalents are titrated with p-hydroxymercuribenzoate suggesting the presence of cystine as well as cysteine residues. Inhibition of the activation of inactive (activatable) enzyme is sigmoidally related to the molar ratio, p-hydroxymercuribenzoate/enzyme with 10–11mol of mercurial compound causing complete inhibition. Active enzyme, free from activating reagents, requires high molar ratios of mercurial compound for rapid inhibition. In terms of p-hydroxymercuribenzoate the enzyme then lacks an essential thiol group.

scholarly journals Complexes of end-functionalized polystyrenes carrying amine end-group with transition metals: association effects in organic solvents

2019 ◽  
Vol 10 (1) ◽  
pp. 4764-4773
Keyword(s):  
Light Scattering ◽  
Organic Solvents ◽  
Capillary Tube ◽  
High Vacuum ◽  
Molar Ratio ◽  
Complex Situation ◽  
Molecular Weights ◽  
Molar Ratios ◽  
Association Behavior ◽  
End Group

Linear end-functionalized polystyrenes of different molecular weights bearing amino end-group (NPS) were synthesized by anionic polymerization high vacuum techniques. The polymers were exposed to copper and iron salts (CuCl2.2H2O and FeCl3.6H2O) to form complexes with specific metal/amino molar ratios. The thermal stability of these complexes was studied by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG), whereas their solution behavior was studied by Low Angle Laser Light Scattering (LALLS), Dynamic Light Scattering (DLS) and dilute solution Viscometry. Extended aggregation phenomena of these complexes were observed in organic solvents. The association behavior was influenced by the molecular weight of the polymer chain, the metal/amine group molar ratio, the chemical nature of the metal and the polarity of the solvent. A complex situation was revealed by DLS showing the existence of equilibrium between aggregates and clusters. Under the influence of shear forces applied in the capillary tube of the viscometer the clusters are disrupted.

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