ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213901

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractThe proton magnetic resonance in polymethyl acrylate, polymethyl methacrylate, and polyethyl methacrylate has been studied between 77 and 400°K. The second moments of the absorption lines are compared with the values calculated for some of the modes of molecular motion possible in these polymers. This comparison leads to the conclusion that motion of the ester methyl and ethyl groups in the respective polymers occurs below 77°K. and that motion of the main chain methyl groups in polymethyl methacrylate and polyethyl methacrylate occurs above 130°K. This interpretation of the results is shown to be in agreement with previous measurements of the mechanical and dielectric properties of these polymers. The shape of the absorption line observed in polymethyl methacrylate at 77°K. was reproduced by a suitably weighted superposition of the absorption lines of rigid and rotating methyl groups and a rigid methylene group confirming that motion of one methyl group occurs below 77°K. in polymethyl methacry

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213902

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractDifferential thermal analysis has been used to study the solid‐liquid transitions of four polyethylenes, an isotactic polypropylene, a series of ethylene‐propylene copolymers, and a physical mixture of polyethylene and polypropylene. The thermograms obtained directly yield the transition temperatures. By calibration, heats and entropies of fusion were also derived from the thermograms. From the heats of fusion, the degree of crystallinity of these polymers has been calculated. Differential thermal analysis can detect a physical mixture of polymers that melt sufficiently wide apart. The thermogram‐peak areas are proportional to the amounts of material present. Convenience and speed make differential thermal analysis a useful tool for characterizing polymeric materials when uniform conditions are maint

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213903

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractThe ultrasonic degradation of macromolecules can be considered to be caused by the rapid pressure changes accompanying the shock wave radiated from a collapsed cavity. Assuming that all the cavities are identical and that the shock wave is similar to that generated by an underwater explosion of TNT, rate constants for the degradation of polystyrene in benzene have been found as a function of molecular weight. The variation in the limiting molecular weight with ultrasonic intensity has been calculated and shown to agree with that obtained experimentally. The theory indicates that the maximum pressure reached during the collapse of a cavity is about 1600 atm.

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213904

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractMolecular weight distributions have been found for fractions of polystyrene degraded ultrasonically in benzene solution at very low concentrations (0.002% w/v). The distributions show that little, if any, of the degradation products include molecules of molecular weight less than 50,000. The variation of the rate constant for the degradation of the molecules with molecular weight follows the theoretical relation being proportional toM2.82derived in Part I up to molecular weights of 106. Beyond this value the rate constant increases at a slower rate. This is attributed to a change in the variation of the shock pressure and rear flank of the shock wave with distance from the cavity. The rate constant for a given fraction reaches a peak at a concentration of about 0.01% w/v after which it falls rapidly with increasing concentration. This is attributed to the formation of a network by the polymer which reduces the rate of the cavity collapse.

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213905

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractWhen polymer single crystals are precipitated from dilute solution all the crystals have very nearly the same basic thickness. This thickness increases with increasing temperature of precipitation. This behavior is shown to result from a growth process in which the rate‐controlling step is the coherent nucleation of new layers of crystal upon the nonfolded planes of existing polymer crystals. The essential feature of the theory is the recognition that a nucleus of folded chains can enlarge easily only in directions parallel to the planes of folds. The theory is concerned primarily with the growth of crystals and only secondarily with their birth. It is shown that for polyethylene at reasonable supercoolings all the crystals will have essentially the same thickness and that this thickness should increase with temperatur

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213906

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractThe nature of the intermolecular interactions involving the CN groups in organic nitriles has been investigated through comparison of the physical properties of nitriles and other organic liquids. Evidence is presented that hydrogen bonding is not a significant factor in these interactions. The CN groups tend to associate in pairs by dipole interaction, leading to partial dimerization in mononitriles and to longer‐range association in dinitriles. The energy of interaction between two CN groups is high, about 8 kcal./mole; it is proposed to call this interaction a CN dipole‐pair bond, by analogy with the hydrogen bond. Equations are derived for energies of interaction between dipoles separated by relatively short distan

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213907

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractThe ferrous iron–ethylenediaminetetraacetic acid–hydrogen peroxide‐initiated emulsion polymerization of styrene has been investigated, potassium palmitate being used as emulsifying agent. It was found that there was acritical concentration of iron, 0.01 part of ferrous iron per 100 parts of monomer, above which the zero‐order rate of polymerization was not appreciably increased. The rate is also proportional to the square root of the hydrogen peroxide concentration and to the soap concentration to the 0.

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213908

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractThe polyaminocarboxylic acids, ethylenediaminetetraacetic acid (EDTA), methylethylenediaminetetraacetic acid (MeEDTA), diethylenetriaminepentaacetic acid (DTPA), and cyclohexanediaminetetraacetic acid (CDTA) have been used to chelate the iron in the system ferrous iron–hydrogen peroxide when it is used as an initiator for the emulsion polymerization of styrene. In each case, the zero‐order rate of polymerization decreased from pH 0.5, when it was identical to that in the absence of any chelating agent, to a minimum value in the pH region 3.5–6.5, after which it rose again. In acid solution the results are not the same as those anticipated from the redox potentials of the ferrous–ferric–chelating agent system at various pH values, and this has been found to be due to the dissociation of the iron chelate at

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213909

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY

摘要:

AbstractThe analysis of simple successive polymer fractionation data by conventional and statistical methods is discussed. The fractionation model originating in the Flory‐Huggins theory of polymer solutions is used to test the alternative methods. The direct statistical methods are shown to be superior to alternative procedures. Such methods approximate the individual fraction distributions by simple statistical distributions (binomial or generalized exponential), the parameters of which are calculated directly from a knowledge of two average molecular weights (M̄nandM

ISSN:0022-3832    

DOI:10.1002/pol.1960.1204213910

出版商:Interscience Publishers, Inc.    

年代:1960

数据来源: WILEY