摘要:

AbstractResults of viscometric and osmotic measurements as well as solubility experiments with isotactic and atactic polystyrene fractions are reported. The relation between [η] andMwas not found to be different for the two types of polymer. On the contrary, the second virial coefficientsBin toluene are appreciably different. Calculated values of the “limiting interaction affinity” φEin toluene and the results of solubility experiments in MEK and in toluene–methanol mixtures show that atactic polystyrene is always more soluble than isotactic polystyrene, regardless of whether the latter is in the crystalline or in amorphous (metastable) state. MEK is shown to be a selective solvent in the separation of the two types of polystyrene. The measure ofBor φEis suggested as a possible measure of the

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410601

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance studies have been made of the proton and fluorine absorptions in powder samples of polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, and polytetrafluoroethylene. Measurements were made over a temperature range of 77 to 300°K., and in some polymers up to 420°K. Narrowing of the absorption curves indicates the onset of motion in the temperature region 280–320°K. The activation energies for the narrowing amount to 2–4 kcal. and frequency factors for the motion are about 106to 107sec.−1, values which are much smaller than those reported for other polymers. Second moments of the absorption curves have been calculated for simple models of motionless and rotating molecules, and have been compared with experiment. The onset of motion in polytetrafluoroethylene is related to transitions reported elsewhere in studies of crystallinity, frictional coefficient, specific heat, and density. Nuclear resonance measurements on fibers of this polymer are in keeping with the view that these physical effects are associated with molecular r

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410602

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractA theory for the tensile strength of rubbers is presented. It gives reasonable agreement with the available experimental data for natural and synthetic rubber. One of the basic postulates of the theory is that, in order for the sample to break, conditions must be such that when one chain breaks the extra load thrown onto its near neighbors causes one of them to break. It appears that the effect of crystallites and filler particles is to decrease the additional load forced onto each of its neighbours when a segment breaks. This makes possible the effective use of higher degrees of crosslinking. The resultant increase in effective network chains is apparently responsible for the superior strength of the materials containing small solid particles, either crystallites or filler. It is also pointed out that the low number‐average molecular weight of GRS lowers the maximum strength of the unfilled polymer by about a factor of two. The effect is not nearly so large in the case of filled rubbe

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410603

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractSpecific heat measurements have been carried out on granular and annealed Marlex 50, a polyethylene polymerized at relatively low pressures, over the temperature range −25 to 150°C. Calculation of the crystallinity yields maximum values of 82.6 and 93.8% for the granular and annealed Marlex 50, respectively. The specific heat of crystalline Marlex 50 at room temperature is slightly less than that previously predicted for a crystalline paraffinic hydrocarbon of infinite chain length. The maximum melting temperature, 134.8°, is about 1.7° less than that of polymethylene and close to the predicted value for a long chain solid hydrocarbon. 90% of the solid Marlex 50 melts over a 15° range of temperature. The shape of the specific heat‐temperature curve can be well reproduced by application of Flory's theory of crystallization in copolymers by considering branch points and chain ends to be the noncrystallizing copolymer units. Negative temperature drifts just below the melting point and low specific heat values just above have not been ex

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410604

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractEmulsion polymerizations of styrene have been carried out with potassium persulfate as initiator and fatty acid soap as emulsifier in the presence of varying amounts ofN,N‐dimethyl‐2,4‐dinitroaniline (DMDNA) and 1‐bromo‐2,4‐dinitrobenzene (BrDNB). The latter two substances are retarders. Rates of polymerization, rates of disappearance of retarder, and polymer molecular weight were determined. The ultraviolet spectrum of the retarded polymer showed conclusively the presence of bound DMDNA while the amount of bound DMDNA was determined by a spectrophotometric acid‐base titration with perchloric acid of the polymer dissolved in benzene. BrDNB was prepared using Br82and the amount of retarder fragments in the polymer determined by radioactive measurement. The quantities of persulfate remaining and of sulfate formed were determined during polymerization strongly retarded by DMDNA. All the results are in quantitative agreement with the following mechanism. The rate‐determining step in initiation is the rate of thermal decomposition of persulfate in water into sulfate free radicals. The sulfate radical reacts with monomer to initiate polymerization. In the absence of retarder, growth is terminated either by chain transfer with monomer or by combination with a second sulfate radical. In the presence of retarder the growing radical may combine with retarder, forming a sluggish free radical to which monomer does not add, and which is terminated by reaction with a second sulfate radical. In this reaction a hydrogen atom is transferred yielding a polymer molecule and

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410605

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractAn expression is obtained in the form of an integral equation of the Fredholm type which correlates the mechanical relaxation distribution of a linear amorphous polymer with its molecular weight distribution. A method of approximate solution of this integral equation is given on the basis of the assumptions that: (1) the relaxation spectrum of a monodisperse sample in the rubbery region is approximated by a box‐shaped function; (2) the steady‐flow viscosity of a monodisperse sample increases with the 3.4 power of molecular weight above a certain critical molecular weight M̄c; and (3) the relaxation modulus (or the real part of the complex dynamic elasticity), Ē, in the initial zone of the rubbery region is independent of molecular weight and may be calculated in terms of Alfrey's approximation. The method permits predicting the molecular weight distribution from experimental relaxation data obtained over the entire region of rubbery timescale, provided the values ofMc, Ē, and M̄z(z‐average molecular weight) of the given sample are known. Stress‐relaxation data on unfractionated samples of polystyrene and polyvinyl acetate are analyzed in terms of this method, and it is found that the predicted molecular weight distributions agree quite satisfactorily with the observed data for both polymers, except in regions of low molecular weight where the theory gives rise to a fictitious maximum and minimum, neither of which is observed in the experimental data. This anomaly is attributed to the effect of the transition region on the initial zone of the rubbery region which is neglected in the present theory. The experimental data on polyvinyl acetate used for the tests are taken from our previous study, and those on polystyrene are newly obtained for this work. Since no complete stressrelaxation data covering the entire region from glassy state to rubbery flow are yet available on polystyrene, those obtained in this work are presented in rather great detail. The relaxation spectrum in the transition region is compared with that of Grandine and Ferry and of Becker from dynamic mechanical measurements in an audiofrequency range, with a fair agreement with the former of the two. The shift factoraTdetermined over the temperature range from about 80 to 150°C. follows a similar curve to that found previously for polyvinyl acetate when reduced to an appropriate reference temperature, and yields a maximum activation energy for relaxation processes of 210 kcal. mole−1at a temperature of 92 ± 1°C. This temperature is in the middle of the reported second order transition temperatures on polystyrene of high

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410606

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractIn order to follow the course of the Arndt‐Eistert reaction on a polymeric system, polymethacryol chloride has been reacted with diazomethane in dioxane solution using different molar ratios of diazomethane/acid chloride at different temperatures. The structure of the reaction products has been determined by chemical methods and by infrared spectrometry. The contents of acid chloride and diazoketone units have been evaluated from chlorine and nitrogen analyses, respectively; conductometric and potentiometric titrations allow determination of the percentages of ketene and pseudo‐acid groups. From these data it is concluded that the first reaction products of diazomethane on an acid chloride unit are diazoketone groups, as expected; however, the interaction of these primary groups with the neighboring acid chloride units yields principally β‐ketocycloketene functions. The presence of these groups and their content have been confirmed by a decarboxylation reaction effected by hydrolysis in acidic medium, during which carbon dioxide is evolved, while the acid content decreases and cyclic ketones are formed. Their presence has also been confirmed by oxidation with dilute nitric acid, which transforms the polymer into polymethacrylic acid. These results of decarboxylation and of oxidation are unreconcilable with the formation of the higher homolog of polymethacrylic acid, the polyisopropenylacetic acid, which would be the normal chainlengthening reaction product of the Arndt‐Eistert reaction. Infrared spectrometry shows, in the triple bond region, absorption bands at 4.65 and 4.73 μ, and, in the double bond region, bands at 5.55, 5.70, 5.80, and 6.10 μ. By comparison with the data in the literature, and especially with the spectrum of the glutaric bisdiazoketone, these different bands have been assigned and their relative intensities interpreted. The spectrometric results confirm the presence of diazoketone and β‐ketoketene groups; moreover, they show relatively low amounts of cyclopentanone rings and of es

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410607

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractIntrinsic viscosities were measured for sharply fractionated polymer in a good solvent and in a poor solvent at several temperatures. They increased with specific volume of the solute, [η] = ΦL3/M. Φ was considered as an empirical constant depending on solute and solvent. Values were determined for polystyrene/toluene and polystyrene/cyclohexane, using light‐scattering measurements for derivation of molecular weights and dimensions. The equation was assumed valid for extrapolation to lower molecular weights and used to estimate molecular dimensions from viscosity/molecular weight data in a range not directly measurable. The results were compared with theoretical calculations of the random coil pro

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410608

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410609

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202410610

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY