Crosslink Density in Polybutadiene

1959 ◽  
Vol 32 (3) ◽  
pp. 706-717
Author(s):  
L. H. Howland ◽  
A. Nisonoff ◽  
L. E. Dannals ◽  
V. S. Chambers
Keyword(s):  
Molecular Weight ◽  
Crosslink Density ◽  
Chain Transfer ◽  
Average Molecular Weight ◽  
Weight Fraction ◽  
Side Reactions ◽  
Polymerization Temperature ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
Rate Of Increase

Abstract 1. A method has been developed for the measurement of crosslink density of diene polymers. This method, which involves the use of radioactive chain transfer agents, is applicable to ungelled polymer prepared under a wide variety of conditions so that any polymerization variable can be studied independently. 2. The crosslink density in polybutadiene decreases with decreasing polymerization temperature. At low molecular weight of polymers, the amount of crosslinking varies linearly with the polymerization temperature. 3. The crosslink density of polybutadiene increases with increasing number-average polymer molecular weight. The rate of increase is less for polymer prepared at −18° C than for that polymerized at 5° to 50° C. This means that, in a polymerization, as the average molecular weight increases with conversion the crosslink density increases. However, when the molecular weight is kept constant, by changes in the modifier loading, the crosslink density of polybutadiene appears to be independent of the degree of conversion attained within the range of 0.12–0.48. 4. The crosslink density of a high molecular weight fraction of polybutadiene was not significantly different from that of the whole polymer (from which about 3% of low molecular weight material had been removed). 5. The kind of initiator system does not affect the crosslink density of polybutadiene, providing the initiator loading is not too high. However, if large amounts of initiator are used in the polymerization, 10% or more of the polymer molecules may not contain mercaptan modifier. 6. Tertiary alkyl mercaptans are necessary for the crosslinking studies because they do not appear to give side reactions. Primary dodecylmercaptan and diisopropyl xanthogen disulfide are unsatisfactory for determinations because they appear to add to the double bonds of the polymer molecule in addition to the usual chain transfer reactions. 7. Incomplete emulsification of monomers in some 5° C recipes apparently increased the crosslink density of polybutadiene by retarding the diffusion of monomer into the monomer-polymer particles.

In Vivo Studies on the Inhibition of Coagulation by Fractionated Heparin and by a Heparin Analogue I. Effects of Heparin Fractions

1981 ◽  
Vol 46 (03) ◽  
pp. 612-616 ◽  
Author(s):  
U Schmitz-Huebner ◽  
L Balleisen ◽  
F Asbeck ◽  
J van de Loo
Keyword(s):  
Molecular Weight ◽  
Day Treatment ◽  
Gel Filtration ◽  
Weight Fraction ◽  
In Vivo Studies ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
Platelet Factor ◽  
Heparin Fractions

SummaryHigh and low molecular weight heparin fractions obtained by gel filtration chromatography of sodium mucosal heparin were injected subcutaneously into six healthy volunteers and compared with the unfractionated substance in a cross-over trial. Equal doses of 5,000 U were administered twice daily over a period of three days and heparin activity was repeatedly controlled before and 2, 4, 8 hrs after injection by means of the APTT, the anti-Xa clotting test and a chromogenic substrate assay. In addition, the in vivo effect of subcutaneously administered fractionated heparin on platelet function was examined on three of the volunteers. The results show that s.c. injections of the low molecular weight fraction induced markedly higher anti-Xa activity than injections of the other preparations. At the same time, APTT results did not significantly differ. Unfractionated heparin and the high molecular weight fraction enhanced ADP-induced platelet aggregation and collagen-mediated MDA production, while the low molecular weight fraction hardly affected these assays, but potently inhibited thrombin-induced MDA production. All heparin preparations stimulated the release of platelet Factor 4 in plasma. During the three-day treatment periods, no side-effects and no significant changes in the response to heparin injections were detected.

Some Osmotic Measurements of the Molecular Weight of a High Molecular-Weight Fraction of Rubber Hydrocarbon

1955 ◽  
Vol 28 (2) ◽  
pp. 504-507
Author(s):  
G. W. Drake
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Average Molecular Weight ◽  
Weight Fraction ◽  
Considerable Proportion ◽  
Prolonged Storage ◽  
High Molecular Weight Fraction ◽  
The United Kingdom ◽  
Molecular Weight Fractions ◽  
Temperate Climates

Abstract Fractionation of the rubber hydrocarbon in temperate climates has usually resulted in high molecular-weight fractions, with a molecular weight of the order of one million. Bloomfield has shown that fresh latex contains a considerable proportion of hydrocarbon having an intrinsic viscosity (η) of 10 or over and, therefore, a molecular weight of well over 106. The fractionation technique used by Bloomfield in Malaya has now been applied by the writer to smoked sheet and to F rubber, working in the United Kingdom. No very high molecular-weight fractions were found in the smoked sheet, but the F rubber yielded a fraction of (η)=7.3 and a number average molecular weight 6×106, determined osmometrically. The average molecular weight of natural rubber when freshly prepared is probably well over a million, and includes a substantial portion having a molecular weight of several millions. By the time smoked sheet has reached temperate climates, the high molecular-weight portion has probably been converted to gel. F rubber, presumably because of its different method of preparation, retains the major part of its high molecular-weight material during prolonged storage.

FRACTIONATION OF LIVER SOMATOMEDIN ACTIVITY BY ULTRAFILTRATION

1974 ◽  
Vol 62 (2) ◽  
pp. 355-361 ◽  
Author(s):  
JENNIFER M. DEHNEL ◽  
P. D. McCONAGHEY ◽  
M. J. O. FRANCIS
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Weight Fraction ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
Cartilage Growth ◽  
The Relationship ◽  
Somatomedin Inhibitors

SUMMARY Plasma somatomedin is the intermediary through which growth hormone (GH) exerts its effects on the growing skeleton. Somatomedin activity may be produced in vitro by perfusion of the liver and kidneys of rats with Waymouth's medium containing GH. The relationship between the activity of plasma somatomedin and somatomedin of hepatic and renal origin has yet to be clarified. Somatomedin from plasma can be separated into active fractions of both high and low molecular weight. Similarly, ultrafiltration of medium containing somatomedin of hepatic origin indicates the existence of two active fractions, one of high molecular weight (greater than 50000) and one of low molecular weight (less than 1000). The latter can be attributed to the release of amino acids, such as serine and glutamine, by the perfused tissue. The high molecular weight fraction is believed to represent GH-dependent somatomedin. Fractions that inhibit production of cartilage matrix are present in liver perfusates as well as in plasma. These results provide further evidence that the liver is a source of GH-dependent somatomedin in vivo. Furthermore, cartilage growth may be controlled not only by the GH-stimulated release of somatomedin by the liver, but also by its release of acid-labile somatomedin inhibitors.

Study of the Carbohydrate Content of Mucus Glycoproteins from Normal and Diseased Colons

1981 ◽  
Vol 61 (2) ◽  
pp. 229-234 ◽  
Author(s):  
J. R. Clamp ◽  
G. Fraser ◽  
A. E. Read
Keyword(s):  
Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Weight Fraction ◽  
Carbohydrate Content ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
Mucus Glycoprotein ◽  
Active Colitis ◽  
High Mannose ◽  
Mucus Glycoproteins

1. Mucus samples obtained from colectomy colons from 10 patients with ulcerative colitis and four patients with Crohn's disease of the colon, together with samples from 10 normal postmortem colons, have been studied. 2. Two glycoprotein fractions were isolated from mucosal scrapings by gel-permeation chromatography. The high-molecular-weight fraction consisted largely of mucus glycoproteins and was further purified to the glycopolypeptides. The low-molecular-weight fraction contained a glycoprotein with a high mannose content. The carbohydrate content of both the mucus glycoprotein and glycopolypeptide fractions were significantly reduced in active colitis. 3. Oligosaccharides were prepared from the mucus glycoprotein material. In the normal material more than half the units contained eight or more monosaccharide residues, whereas in the disease material the bulk of the units were smaller than this.

scholarly journals Molecular-mass distribution of humus acids of taiga soils

2021 ◽  
Vol 4 (4) ◽  
Author(s):  
E. D. Lodygin ◽  
R. S. Vasilevich
Keyword(s):  
Molecular Weight ◽  
Molecular Mass ◽  
Molecular Mass Distribution ◽  
Weight Fraction ◽  
Low Molecular Weight ◽  
Distilled Water ◽  
High Molecular Weight Fraction ◽  
Molecular Weights ◽  
Podzolic Horizon ◽  
Agricultural Use

Purpose of the study: to reveal the influence of hydromorphism and agricultural use on the molecular-mass distribution (MMD) of humic (HAs) and fulvic acids (FAs) isolated from the soils of the European northeast of Russia. To assess the influence of the acidity of the medium on the MWD of FAs. Place and time of the event. The studies were carried out on the territory of the middle taiga (Maksimovsky station of the Institute of Biology of the Federal Research Center of the KSC UB RAS, located 8 km west of the city of Syktyvkar and the field of the Syktyvkar state farm, 5 km south-west of Syktyvkar, on the watershed of the Sysola and Vazhel-yu rivers) and northern taiga (3 km west of the Troitsko-Pechorsk station). The objects of the study were humic substances isolated from typical podzolic (Eutric Albic Retisol (Loamic)), gleypodzolic (Eutric Albic Stagnic Retisol (Loamic)), peaty-podzolic surface-gleyed (Eutric Albic Stagnic Histic) Retisol (Loamic Eutric Albic Retisol (Loamic)) soils. The soil sampling period is from 1 to 30 August 2014. Methodology. Quantitative analysis of the MMD of HA and FA preparations was performed using liquid size exclusion chromatography (gel chromatography) on Sephadex G-25 and G-100 gels with continuous automatic registration of the optical density of the eluate (λ = 280 nm) in a quartz flow cell, K 9 × 60 cm column (Pharmacia, Sweden). Distilled water, 0.05 M NaOH solution, and Tris-HCl buffer with pH = 8.2 were used as the eluent. Main results. Studies of the MMD of humic substances have been carried out. It was found that HAs contain three fractions with different molecular weights: ≥ 150 kDa, 73–80 kDa, and 13–23 kDa; FAs – two fractions: ≥ 5 kDa, 1–2 kDa. The low molecular weight of FAs, together with a large amount of oxygen-containing functional groups, contributes to their better solubility and migration ability in soils. The HAs of automorphic soils are characterized by a high content of low molecular weight fractions, and the proportion of the high molecular weight fraction in the HAs of the litter is 1.5–2.0 times higher than in the HAs of the podzolic horizon, which may be due to the migration of the low molecular weight fraction down the profile. The high proportion of the acidic low molecular weight fraction in the podzolic horizon promotes the decomposition of soil minerals and their leaching into the illuvial horizon. The influence of agricultural use of soils on the fractional composition of humic compounds is estimated. A sharp increase in the share of the high molecular weight fraction in the preparations of HAs of arable podzolic soil by 2–4 times compared with the HAs of virgin podzolic soils was noted, which is due to the cultivation of the arable horizon, the nature of the incoming plant residues and the increased microbiological activity of the developed soils. The effect of acidity of the medium on the character of chromatograms of FA preparations isolated from the main types of soils of the Komi Republic was studied. It has been shown that in the region of high pH values of the eluent 9–13, the absence of fractionation is associated with the association of FAs, a change in their conformation, and the effect of “over-exclusion”. Elution with distilled water (pH = 6.5) allows the separation of FAs into two fractions with molecular weights ≥ 5 kDa and 1–2 kDa.

scholarly journals Molluscicidal Polyphenols from Species of Fucaceae

2008 ◽  
Vol 3 (2) ◽  
pp. 1934578X0800300
Author(s):  
Asmita V. Patel ◽  
David C. Wright ◽  
Maricela Adrian Romero ◽  
Gerald Blunden ◽  
Michael D. Guiry
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Algal Species ◽  
Weight Fraction ◽  
The Other ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
Bifurcaria Bifurcata ◽  
Marine Algal ◽  
Molluscicidal Activity

The aqueous fractions of the dry methanol extracts (500 ppm) of sixty marine algal species were screened for molluscicidal activity against Biomphalaria glabrata, which is an important host of the bilharzia-causing Schistosoma species. The majority of the extracts tested were inactive at the concentration used, but those of Fucus serratus, F. vesiculosus, Pelvetia canaliculata, Ascophyllum nodosum, Halidrys siliquosa, Bifurcaria bifurcata, Dictyota dichotoma and Halopithys incurva all showed significant molluscicidal activity. Treatment with polyvinylpolypyrrolidone (PVPP) either removed or drastically reduced the activity of the extracts of F. serratus, F. vesiculosus, P. canaliculata, A. nodosum, Halidrys siliquosa and Halopithys incurva, which suggested that the active compounds in the extracts of these species were polyphenolic in nature. The active extracts of the other two seaweed species did not appear to be affected by treatment with PVPP. Dialysis of the active extracts against distilled water separated them into high and low molecular weight fractions. In the case of the two Fucus species, P. canaliculata and A. nodosum, the activity resided in the high molecular weight fraction, whereas with all the other species, the activity was found in the low molecular weight fraction. 1H NMR spectroscopic examination of the active extracts confirmed that the molluscicidal components of the extracts of the Fucus species, P. canaliculata and A. nodosum were high molecular weight polyphenols.

Cartilage fucoproteins with sites for cross-linking by transglutaminase

1987 ◽  
Vol 65 (4) ◽  
pp. 280-285 ◽  
Author(s):  
J. Michael Bowness
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
High Performance ◽  
Specific Activity ◽  
Weight Fraction ◽  
Dry Weight ◽  
Insoluble Fraction ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
Collagen Iii

Slices of various types of cartilage were incubated with either L-[6-3H]fucose or [1,4-3H(N)]putrescine. Homogenization of the slices and fractionation of the homogenates showed for both labels that an insoluble collagenase-resistant fraction had the highest specific activity (dpm/mg dry weight). Examination of an exhaustive proteolytic digest of this insoluble fraction by ion-exchange high performance liquid chromatography showed the presence of γ-glutamyl[3H]putrescine. Chromatography of solubilized [3H]fucoprotein fractions showed the presence of several low molecular weight peaks, as well as high molecular weight material. Incubation of [3H]fucoprotein extracts with transglutaminase increased the high molecular weight peaks and decreased the low molecular weight ones. Incubation of the cartilage slices with L-[3H]fucose plus 0.5 mM dansylcadaverine, an inhibitor of transglutaminase, caused a decrease in the insoluble and high molecular weight fraction relative to the low molecular weight peaks. It is hypothesized that this is due to inhibition of cross-link formation between fucoprotein components of the cartilage which are transglutaminase substrates. One major low molecular weight peak, which labels with both fucose and putrescine, corresponds in size with the 15 000 subunit of collagen III aminopropeptide, which is known to be a substrate for transglutaminase.

scholarly journals The Antiproliferative Activity of Sclerotia ofLignosus rhinocerus(Tiger Milk Mushroom)

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
M. L. Lee ◽  
N. H. Tan ◽  
S. Y. Fung ◽  
C. S. Tan ◽  
S. T. Ng
Keyword(s):  
Molecular Weight ◽  
Cancer Cells ◽  
High Molecular Weight ◽  
Antiproliferative Activity ◽  
Human Lung ◽  
Weight Fraction ◽  
Low Molecular Weight ◽  
Cytotoxic Action ◽  
High Molecular Weight Fraction ◽  
Human Breast

Lignosus rhinocerus, the tiger milk mushroom, is one of the most important medicinal mushrooms used by the indigenous people of Southeast Asia and China. It has been used to treat breast cancer. A cold water extract (LR-CW) prepared from the sclerotia ofL. rhinoceruscultivar was found to exhibit antiproliferative activity against human breast carcinoma (MCF-7) and human lung carcinoma (A549), withIC50of 96.7 μg/mL and 466.7 μg/mL, respectively. In comparison, LR-CW did not show significant cytotoxicity against the two corresponding human normal cells, 184B5 (human breast cell) and NL 20 (human lung cell). DNA fragmentation studies suggested that the cytotoxic action of LR-CW against cancer cells is mediated by apoptosis. Sephadex G-50 gel filtration fractionation of LR-CW yielded a high-molecular-weight and a low-molecular-weight fraction. The high-molecular-weight fraction contains mainly carbohydrate (68.7%) and small amount of protein (3.6%), whereas the low-molecular-weight fraction contains 31% carbohydrate and was devoid of protein. Only the high-molecular-weight fraction exhibited antiproliferative activity against cancer cells, withIC50of 70.0 μg/mL and 76.7 μg/mL, respectively. Thus, the cytotoxic action of the LR-CW is due to the high-molecular-weight fraction, either the proteins or protein-carbohydrate complex.

Tumor Uptake of High and Low Molecular Weight Fractions from 67Ga-Citrate Labelled Blood Plasma

1984 ◽  
Vol 23 (02) ◽  
pp. 59-61 ◽  
Author(s):  
M. C. Crone ◽  
P. Thouvenot ◽  
F. Brunotte ◽  
C. Marchai ◽  
J. Robert ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Blood Plasma ◽  
High Molecular Weight ◽  
Gel Filtration ◽  
Weight Fraction ◽  
Blood Protein ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
67Ga Citrate

SummaryBlood plasma from tumor-bearing rats was incubated with 67Ga-citrate, and two fractions of high molecular weight (proteins) and low molecular weight were isolated by dialysis and by gel-filtration chromatography. Both fractions showed a different in vivo uptake by DS-sarcoma-bearing animals, the high molecular weight fraction being accumulated to a lesser extent. Compared to 67Ga-citrate the low molecular weight fraction showed a different uptake which for most tissues was significatively higher. This behavior suggests the presence of 67Ga in chemical forms other than citrate in the low molecular weight fraction. The lower uptake of the blood protein fraction is discussed.

Sign in / Sign up

Export Citation Format

Share Document