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61.
62.
These investigations are concerned with water-polymer interactions in polymer latices. It is known that water can act as a plasticizer for many solid polymers and cause a reduction in the glass transition temperature, Tg, of the amorphous regions. Experiments were carried out to determine whether pulsed n.m.r. techniques could be used to study the Tg of a polymer suspension and hence the influence of water and electrolyte on it. From T1 and T2 proton relaxation measurements as a function of temperature on polystyrene latex systems it was shown that the presence of water lowers the Tg of the polymer particles (by about 10°C), the effect being slightly greater in the presence of concentrated electrolyte. The extent of electrolyte penetration into the particles was deduced by studying relaxation as a function of particle diameter in latices containing paramagnetic Mn2+ ions. Using simple theories of relaxation and spin diffusion it was concluded that for all but the smallest particles electrolyte penetration is restricted to a very thin shell of the order of 1 nm. These conclusions were supported by the results of similar measurements on PTFE particles. 相似文献
63.
Edward C. Nelson 《应用聚合物科学杂志》1985,30(7):2779-2786
The homogeneous graft copolymerization of acrylamide (AM) onto cellulose initiated by t-butylperoxy-2-ethylhexanoate in a cellulose solvent, N-methylmorpholine oxide (NMMO), was investigated. The method afforded water-soluble PAM-g-cellulose copolymers in fair yields. The copolymers produced are of low molecular weight (50,000–100,000 M?w). Little apparent homopolymerization was observed. 相似文献
64.
Edward Kostansek 《Journal of Coatings Technology and Research》2004,1(1):41-44
Coagulation of latex particles is most often carried out in the diffusion limited aggregation (DLA) regime where the time
for coagulation to take place is on the millisecond timescale. This process produces aggregates of low density, irregular
shape, and a broad particle size distributions. When the coagulation is carried out in the reaction limited aggregation (RLA)
regime, a coagulation time of about 1–120 sec, the system can be controlled by mixing to yield dense, spheroidal aggregates
with a very narrow particle size distribution. The important variables in the RLA process for butyl acrylate/methyl methacrylate
(BA/MMA) latexes were found to be mixing intensity, latex copolymer composition, and coagulation temperature. Dried aggregates
formed in the RLA process were found to have excellent powder flow properties and low dustiness. 相似文献
65.
Michael J. Banach Stephen J. Clarson Gregory Beaucage Jason Benkoski Tom Mates Edward J. Kramer Richard A. Vaia 《应用聚合物科学杂志》2002,86(8):2021-2024
For many microelectronic and optoelectronic applications, polymer thin films require the addition of small molecules. However, the thin‐film geometry and associated processing techniques will influence the final morphology and compositional distribution of the constituents. It is therefore important that these be examined directly rather than inferred from bulk measurements. As an example system, the concentration and distribution of Disperse Red 1 (DR1) molecules in poly(methyl methacrylate) thin films were examined. Ultraviolet visibility spectroscopy and dynamic secondary ion mass spectrometry indicate that the composition of the molecules decreased dramatically with thermal treatment of the film. The sublimation of the chromophore was observed to occur at temperatures well below the melting point of the small molecule and the glass transition of the pure polymer; this solute loss manifested itself in changes in the glass transition temperature of the film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2021–2024, 2002 相似文献
66.
67.
J. Edward Hunter 《Journal of the American Oil Chemists' Society》1981,58(3):283-287
A major objective of commercial processing of soybean oil into edible products is to remove unwanted impurities from the oil
with the least possible effect on nutritional quality of the oil. Soybean oil is an excellent dietary source of essential
linoleic acid and also of tocopherols, which serve as sources of vitamin E and natural antioxidants. The data presented in
this report indicate that the nutritional quality of soybean oil is largely retained after typical commercial processing conditions.
Hydrogenation does reduce the level of essential fatty acids; however, typical commercial salad and cooking oils and shortenings
made from partially hydrogenated soybean oil retain nutritionally significant levels of essential fatty acids. Tocopherols
also are present at high levels in the finished oil. Among the unwanted components of crude soybean oil which are effectively
removed by processing are pesticide residues, phosphatides, free fatty acids, color pigments, and compounds causing objectionable
odors and flavors. 相似文献
68.
Theerythro andthreo isomers of methyl 9,10-dihydroxyoctadecanoate and thethreo isomer of methyl 12,13-dihydroxy-cis-9-octadecenoate were converted into methylcis- andtrans-9-octadecenoate and methylcis-9,rans-12-octadecadienoate, respectively, by reaction of the dihydroxy ester with triethyl orthoformate to give the 2-ethoxy-1,3-dioxolane
which was thermally decomposed to the unsaturated ester. 相似文献
69.
Summary Cholesterol is a universal constituent of all animal cells and therefore occurs in all foods of animal origin. Cholesterol
is the mother substance of bile acid and of sex hormones and has other important physiological roles. Cholesterol is synthesized
in the body from acetate obtainable from ingested carbohydrate, fat. or protein, of animal or vegetable origin.
The fate of cholesterol in the body has not been definitely established. The cause of atherosclerosis is unknown. Atherosclerosis
occurs in young as well as old individuals. Atherosclerosis is the number-one killer today.
Diagnosis of atherosclerosis in the healthy individual is not possible. Treatment of atherosclerosis is empirical. Reduction
of blood cholesterol levels by dietary means is difficult under conditions consonant with good nutrition. A well-balanced
intake of all available foods on a modified total caloric basis appears to be the practical approach to the problem of fat,
cholesterol, and atherosclerosis.
Presented at the 47th Annual, Meeting, American Oil Chemists’ Society, Houston, Tex., April 23–25, 1956. 相似文献
70.
This paper presents a simplified method for the chemical synthesis of cholest-4-en-3-one, which is a naturally occurring steroid
and a salient intermediate in steroid chemistry. Pyridinium chlorochromate (PCC) in refluxing benzene has been found to be
an effective and convenient reagent for the oxidation and concomitant isomerization of cholest-5-en-3β-ol (cholesterol) to
cholest-4-en-3-one in high yield. Also described are the carbon-13 nuclear magnetic resonance spectral properties of cholest-4-en-3-one
and of the isolated reaction intermediate cholest-5-en-3-one.
Based on a paper presented at the Symposium on Plant and Fungal Sterols: Biosynthesis Metabolism and function held at the
AOCS Annual Meeting, Baltimore, MD, April 1990. 相似文献