摘要:

AbstractIn this paper some details are given for the construction of a simple balance for the measurement of stress relaxation at constant elongation. A simple means of obtaining equal strain in the two parts of the strained specimen is provided. By means of four typical stocks covering the widest possible range of aging resistance it is shown that the stress relaxations give approximately the same estimate of stability as does the normal Geer test using 2 mm. dumbbell specimens. As a measure for stress relaxation the time is used that is required to obtain 50% of the value of the interpolated modulus at 200% elongation 6 seconds after the straining zero time at 110°C. The parameter for the aging test is the time in days at 70°C. for the 50% value of tensile strengths. The range for the stress relaxation parameter may be estimated to 8–1200 min. and the aging parameter from 10–600 days. Finally the concordance of temperature coefficient for relaxation and oxidation rates is

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070201

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractCollagen exhibits a low angle x‐ray diffraction pattern corresponding to a spacing of about 650 A. On denaturation (shrinking) this pattern disappears and does not return, regardless of how the material may be treated subsequently. It has been found that, when collagen tendons are stretched taut in a clamp, immersed in water, and then subjected to temperatures above the shrink temperature, the intensity of the low angle pattern diminishes appreciably. This has been interpreted as a decrease in the concentration of the structure which gives rise to the pattern and was assumed to be due to a melting of the crystalline structure of collagen. At constant temperature (above the shrink temperature), the low angle pattern continually decreases in intensity with increased shrinkage until it disappears completely. The extent to which the sample must be shrunk before the pattern disappears is dependent upon the temperature and increases with decreasing temperature.On analyzing the data quantitatively, using the theories of crystallization for linear polymers developed by Flory, it was possible to calculate a heat and entropy of shrinkage. The values obtained for these quantities indicate that the fusion is a stepwise process involving very few amino acid residues in each step (perhaps only one or two residues).Experiments were carried out on collagen shrunk in water and in formamide, as well as on formaldehyde tanned collagen shrunk in water. It was found that the heat and entropy of shrinkage apparently decrease with increasing tendency toward swelling. Thus the heat of shrinkage for formaldehyde tanned collagen is greater than for untanned, and the heat of shrinkage for native collagen is greater in water than in formamid

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070202

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractA spectrometric technique for the determination of refractive indices of liquids and polymers over a temperature range of −70 to +70°C. has been developed and used to establish the absolute accuracy, within =0.0004 refractive index units, of a more convenient refractometric method previously described. Refractive index values are reported for dimethyl phthalate from + 70 to +15°C.; polyvinyl acetate from + 65 to −70°C.; and tricresyl phosphate from +30 to −80°C. The refractometric values are within =0.0004 or less units of the spectrometric values over this range. The data for tricresyl phosphate locate two apparent second order transitions at −47 and at −62°C. The higher value (−47°C.) is observed with thoroughly dried tr

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070203

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractAnalysis of results of experiments on dielectric relaxation of polyvinyl chloride plasticized with tricresyl phosphate and with dioctyl phthalate gives values for heats and entropies of activation for dielectric relaxation rather lower than have been published in the literature for lower frequency ranges. The discrepancy may be due to a variation of heat of activation with temperature. A theoretical relation has been derived for the variation of heat and entropy of activation of dielectric relaxation with plasticizer content. The temperature dependence of the secondary high frequency loss factor maximum in unplasticized PVC has been ascertained, and some aspects of the relation between electrical and mechanical relaxation times and the second‐order transition point have been discusse

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070204

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractThe relations between stress, strain. and time in the tensile creep under constant load of polyvinyl chloride plasticized with dioctyl phthalate have been studied experimentally over a range of temperatures and compositions. It is concluded that existing theories are not adequate to deal with large strains, nonequilibrium conditions, and a distribution of relaxation times. The variables stress, strain, and time may be separated at low loads for “soft” compositions but not for “hard” compo

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070205

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractButadiene‐styrene copolymers have been prepared at subfreezing temperatures by means of redox recipes employing inorganic salts as freezing point depressants. Specific salt‐emulsifier combinations are required for optimum rates of polymerizations. With a sufficient amount of the inorganic salt to lower the freezing point of water 10°C., the sodium chloride–potassium caprylate combination resulted in a 60% conversion in 4.6 hours, the calcium chloride–sodium hexyl sulfate combination resulted in a 41% conversion in 24 hours, and the calcium chloride–alkyl aryl polyether alcohol combination resulted in a 58% conversion in 18.5 hours.Low molecular weight mercaptans such astert‐butyl mercaptan can be employed as practical modifiers for this recipe.Certain of the physical properties of the salt antifreeze copolymers prepared at −10°C. are superior to those of copolymers prepared at the same temperature by means of conventional recipes. The ease of processing and the heat‐aged properties are exceptional. One copolymer after 24 hours of aging at 100°C. withstood 118,000 flexures before a puncture increased to one inch in length at 99°C. The superiority of the product is attributed to the precipitation of the copolymer during the course of

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070206

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractThe viscosities of dilute solutions (0.05, 0.1, and 0.2 g. per 100 ml.) of relatively high nitrogen content nitrocelluloses, weight‐average molecular weightsca.100,000, have been studied using homologous series of methyl ketones, alkyl acetates, and dialkyl phthalates as solvents. The simple form of the Huggins equation,\documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{sp} /c = [\eta] + k'[\eta]^2 c $\end{document}does not appear to hold, plots of ηsp/cagainstcbeing generally curved. The results are capable of expression by\documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{sp} /c = A + Bc + Cc^2 $\end{document}whereAequals [η] andBthe initial slope. Values ofBandAappear to be related to solvent power as determined by the volume of hexane required to cause initial phase separation from solution, good solvents giving higher values ofBandAthan poor. The variation ofBwith solvent is more marked than that of [η] and may reflect differences in degree of coiling of chains in different solvents. Values ofB/[η]2(Hugginsk′) do not generally decrease with solvent power increase. The slopes of Martin plots divided by intrinsic viscosities are not generally related to solvent power in the manner observed by Spurlin with solutions of ethyl ce

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070207

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractThe general theory of the deformation of viscoelastic substances developed in two previous papers for the one‐dimensional case is now extended to three dimensions. The integro‐differential equations obtained are generalizations of the well‐known Navier‐Cauchy equations and, like these, only apply to small deformations.Some special cases are considered in detail and lead to interesting conclusions. In particular, the theory predicts that for incompressible high polymers, one should obtain the same creep and relaxation functions when the material is subjected to extension, torsion, or

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070208

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractContrary to some published reports, the vinyl esters of saturated fatty acids polymerize readily and rapidly. Vinyl oleate, when present in excess of 5%, and oxygen exert marked retarding effects.Techniques are described for the free‐radical‐initiated polymerization of the vinyl esters of caprylic, capric, lauric, myristic, palmitic, and stearic acids in bulk, dispersion, solution, and emulsion. Some data are given for polymerization in the presence of chain‐transfer agents, such as carbon tetrachloride, dodecylmercaptan, and ethylbenzene. Conditions are reported for obtaining degrees of polymerization from about 2 (when chain‐transfer agents are employed) to 10,000 (weight average). The weight average degree of polymerization increases markedly as the conversion increases, particularly above 80%. Even up to extremely high conversions, soluble polymers are obtained in most cases.Solubility characteristics, transition point data, molecular weights (osmometric and light‐scattering), and isolation and purification techniques are also

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070209

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY

摘要:

AbstractThe elastoviscous behavior of polyisobutylene may be interpreted in terms of a mechanical model consisting of a distribution of Maxwell elements connected in parallel. The structure of this “generalized Maxwell model” is specified by the distribution of relaxation times of the component elements. The relaxation of stress curve of the material is directly related to the distribution of relaxation times, and general expressions for the bulk viscosities (tensile and shear) of such a system in terms of the distribution of relaxation times are readily obtained.A simple “box distribution” of relaxation times is described which can be used to approximate the relaxation behavior of polyisobutylene at the long‐time end of the relaxation time spectrum, and in terms of which the expressions for bulk viscosity reduce to very simple form. The parameters specifying this distribution may be determined from experimental relaxation curves by a simple graphical method. Values of these parameters as a functions of molecular weight and temperature are computed, by use of these data. It is shown that bulk viscosity values calculated from relaxation data by this method are in good agreement with experimental values for both tensile and shear deformations, and for both unfractionated and fractionated polymers. Measurements of viscosity and of relaxation of stress can thus be directly correlated, and could be used in combination to characterize elastoviscous properties over wide ranges of molecular weight and te

ISSN:0022-3832    

DOI:10.1002/pol.1951.120070210

出版商:Interscience Publishers, Inc.    

年代:1951

数据来源: WILEY