摘要:

AbstractCorn, wheat, and potato starch were fractionated into their amylose and amylopectin components by selective extraction of amylose in hot water after the starch had been pretreated by heating in aqueous mixtures of glycerol,n‐butanol, Pentasol, Cellosolve, or dioxane. About three‐fourths of the amylose was leached in relatively pure form from starch in the first extraction at 98°C. The granule residue, sedimented by centrifugation, was separated as relatively pure amylopectin after two or more additional extractions. Retention of the coherent structure of the granule in the extracted residue emphasizes the importance of amylopectin to granule properties. Amylose fractions isolated from successive extractions had progressively lower intrinsic viscosities and absorption coefficients of their iodine complexes indicating that this component was subfractionated according to molecular size and/or structure. X‐ray diffraction patterns of the pretreated starches indicated that a complex of amylose and organic solvent was formed which may account for the increased solubility of amylose after pretreatment. Evidence is presented which shows that little, if any, amylose occurs in the crystalline regions of granular st

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811601

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractA technique was developed which allows the determination of essentially pure tensile strengths of single interface adhesive samples. Utilizing a suitably modified ultracentrifuge, model adhesive systems were ruptured in an attempt to obtain relative strengths of adhesive bonds in the interface.

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811602

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

Abstractn‐Amyltriethoxysilane and phenyltriethoxysilane were hydrolyzed in organic solvents in the presence of acidic or basic catalysts. The bulky substituents allow relatively large amounts of low‐molecular‐weight partial hydrolysis products to be isolated and stabilize the silanol functions present against further condensation. Cyclic ethoxypolysiloxanols in the molecular weight range 500–1000 are principal products of acid catalyzed hydrolysis. More extensive condensation occurs under alkaline conditions. Relatively high yields of low‐polymeric silsesquioxanes (octamers and possibly hexamers) are then obtained. The major product obtained from phenyltriethoxysilane, when hydrolyzed in a ketone solvent with a quaternary base as catalyst, is an amorphous high polymer virtually free of functional groups. In inert solvents in the presence of traces of catalyst a very facile rearrangement occurs, giving the octamer (and possibly the hexamer) in very h

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811603

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractA procedure is described for measuring the surface tension of polymeric liquids whose bulk viscosity is at least 1500 times that of glycerol. The procedure is based on the determination of the force necessary to separate two spheres held in contact by the test liquid. A series of silicones was examined. Following a relatively sharp rise in surface tension for the lower members, the rate of increase in surface tension with bulk viscosity is extremely small and seems to be approaching a constant value.

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811604

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractUsing a modification of the vibroscope technique, studies have been made of the sorption kinetics of water vapor in single wool fibers. Small changes in water content, described as interval sorption and desorption, occur in two stages, the first occupying a few minutes and the second many hours (at room temperature). This behavior is similar to that recently reported for interval sorption of organic vapors in “glassy” polymers (e.g., acetone in cellulose acetate). The first stage of sorption is considered to be due to diffusion in accordance with Fick's law; the slow increase in concentration during the second stage is thought to result from partial relaxation of the swelling stress. Large changes in water content are described as integral sorption and desorption. In integral sorption the slow second stage of sorption is not observed; the explanation is thought to be that relaxation of swelling stress, and hence the second stage, are greatly accelerated by the transient stress associated with the steep concentration gradient present during integral sorption. The slow second stage is present in integral desorption, the probable reason being that in this case there is no steep concentration gradient. Integral sorption to a given value of relative humidity (R.H.) results in a higher equilibrium water content than if the same R.H. is reached in a series of interval steps. This effect is thought to be related to the hysteresis which is observed in the isotherm in a sorption‐desorption cycle; the transient stress present in integral sorption leaves the material in the same condition as if it had been brought down the desorption curve of the isotherm. The sorption hysteresis is thought to result from metastability of the interchain bonds which undergo relaxation in the second stage of interval sorption and desorption. All the effects observed are likely to be qualitatively characteristic of vapor sorption in any polymer at temperatures below the second‐order tra

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811605

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractVinylpyridine was polymerized in suspension, using azobis‐iso‐butyronitrile as initiator. The polymer was fractionated by partial precipitation from methanol solutions by addition of toluene to cloud point in chilled solution and then raising the temperature. Viscosities of four fractions were determined at 25, 50, and 70° in absolute ethanol. Rayleigh ratios and scattering asymmetry were determined for eight fractions; from the corresponding Zimm plots, molecular weights, coil diameters, and virial coefficients were determined. Addition of ammonia was found necessary at low concentrations to suppress ionization due to traces of acid impurities. Addition of water (a nonsolvent) lowers the second virial coefficient. Molecular weights were determined for two fractions by osmotic pressure. In absolute ethanol, the results are summarized by the equation [η] = 2.5 × 10−4M0.68; experimental range 0.102 ⩽ 106M⩽ 1.85. The second virial coefficient from light scattering was 4.2 ± 0.3 × 10−4, independent of molecular weight; the osmotic values agreed within experimental error. The Flory constant was found to be 2.1 ± 0.3 × 1021. Extrapolation for the θ‐point leads to the rough estimate θ ≈ −50°C. Evidence is presented which shows that polyvinylpyridine

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811606

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractA theory for the infrared dichroism of a crosslinked, rubber‐like amorphous polymer is described. The dichroism of a typical rubber is estimated to be measurable. The dichroism‐stress ratio is independent of strain and degree of crosslinking and serves as a measure of the number of monomer units per statistical segment, an index of chain stiffn

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811607

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe observed activity of boron fluoride‐dimethyl formamide as a catalyst for the polymerization of acrylonitrile has been studied. It has been found that oxygen is a necessary third component, and that the polymerization is a free radical process. Evidence is presented that oxygen reacts with acidic complexes of dimethylformamide to give peroxides of the type HCON(CH3)CH2OOH, which acts as typical peroxide initiator

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811608

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractLifetimes of polymer radicals were determined by a direct flow technique. The variation of yield of polymer with the period between initiation by an ultraviolet source and destruction in an inhibitor solution was determined by spectrophotometric analysis. A swiftly falling stream of monomer was irradiated by a sharply focussed beam of intense ultraviolet radiation, and the time of radical growth was controlled by varying the distance of fall at a constant flow rate. The variation of yield of polymer with the time interval between photochemical initiation an destruction in an inhibitor solution was determined by spectrophotometric analysis of the polymer formed. A polished elliptical reflector was used, instead of the customary quartz lenses, with the source and stream at the foci of the ellipse. A water‐jacketed capillary was employed to eliminate spurious thermal initiation. Radical lifetimes of 0.24 seconds for styrene and 1.80 seconds for butyl acrylate were obtained. The data were compared with values calculated on the basis of non‐stationary state kinetics in a flow sys

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811609

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe effects of pile irradiation on the damping and resonant frequency of a “high pressure” polyethylene has been investigated over a temperature range from 80 to 550°K. in the audiofrequency region using an apparatus which drives rod‐like specimens in their transverse modes. Using irradiation dosages which result in approximately 4% crosslinking or greater, the mechanical loss peaks found at about 165, 265, and 355°K. in polyethylene are altered. Definite changes in the resonant frequency or modulus‐temperature plots also occur. The 355°K. peak, attributed to the melting of the crystalline portions of the sample, decreases in height and shifts to lower temperatures with increasing irradiation dose. A decrease in the height of the 265°K. peak accompained by a shift to higher temperatures takes place. The 165°K. peak initially increases in height and peak temperature but at higher dosages a marked decrease in the damping maximum occurs. The damping behavior in the 165 and 265°K. regions is discussed in terms of diffusional motion of chain segments in the amorphous pol

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202811610

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY