摘要:

AbstractThe kinetics of the sorption and desorption of methylene chloride by cellulose acetate and polystyrene have been studied by following the increase in mass of a polymer sheet suspended from a quartz spring in an atmosphere of the vapor. A tenfold change in the molecular weight of polystyrene does not alter the sorption rate, but a slight increase in rate is obtained when the molecules of this polymer are given a large unidirectional orientation in the plane of the polymer sheet. In agreement with other work, a considerable increase in both sorption and desorption rate is obtained by increasing the pressure of the solvent vapor. Previously it had been shown that a plot of the mass of sorbed vapor against the square root of the time has a slope that increases with time. It was shown that this peculiar characteristic of the sorption kinetics could not be accounted for by a purely concentration dependent diffusion coefficient, and it was suggested that it might be due either to a slow response of the diffusion coefficient to change in solvent concentrationor to the stresses set up between the swollen and unswollen parts of the polymer. Here it is shown that neither hypothesis alone will account for all the observed effects of the thickness of the polystyrene or cellulose acetate sheet upon the sorption and desorption kinetics. Sorption experiments on polymer sheet already containing some dissolved solvent do not show this peculiar characteristic of increasing slope when the concentration difference between the start and the end of the experiment is small, but when this is large very peculiar curves are obtained. The effects can be reconciled with either of the proposed mechanisms. Measurements of the changes in area during sorption and desorption have been measured on polystyrene sheet and these lend support to the strain hypothesis but also indicate that some plastic, as well as elastic, deformation of the polymer takes place during sorption.

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110201

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractCertain abnormalities in the compositional relationship of styrene/maleic anhydride copolymers indicate that nonterminal monomer units in a polymer radical (principally the penultimate unit) can detectably influence radical reactivity, through electrostatic interactions with reacting monomer molecules. This effect should be particularly pronounced for monomers of type CHXCHX, where X is a dipole. Several examples from the literature are cited to show that abnormal dependences of copolymer composition on monomer concentration ratio can be explained along these lines. It is suggested that the recently observed variation of cross‐termination velocity coefficients with composition of the monomer mixture is attributable to a similar ca

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110202

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractCopolymerization studies have been made on the three two‐component systems formed by the monomers methyl acrylate, 2‐vinylpyridine, and dichlorostyrene, and values of the monomer reactivity ratios were determined. Terpolymers were prepared from mixtures of these same monomers, and their compositions were compared with those predicted from the kinetic data for the copolymerizations. Measurements of dissymmetry of scattered light, molecular weight, and viscosity were made on solutions in acetic acid and in methyl ethyl ketone of a terpolymer containing 37 mole per cent methyl acrylate, 47 mole per cent 2‐vinylpyridine, and 16 mole per cent dichlorostyrene. The molecular weight of the terpolymer is essentially the same in the two solvents but the polymer chain is more extended in acetic acid than in methyl ethyl ketone. In nitromethane solutions of the terpolymer the ηsp/cvalues increase sharply with decreasing concentration. This increase is eliminated if the solutions also contain 0.01 mole per liter of a substituted quaternary ammonium iodide. These facts indicate that the polymer behaves as a polyelectrolyte in nitromethane, presumably because of reaction between theaci‐form of the solvent and the vinylpyridin

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110203

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractThis report assembles and correlates published data relating to the effect of temperature of polymerization on the structural composition of butadiene polymers, that is, on the relative percentages of polymer double bonds, derived from butadiene, in the 1,2 (vinyl),trans‐1,4, andcis‐1,4 configurations. The data support, and are not in conflict with, the following conclusions: (1) The percentages of vinyl,trans, andcisdouble bonds in emulsion polymers of butadiene are determined primarily by the temperature of polymerization in the fundamental way that is characteristic of systems of simultaneous competing reactions. (2) Other environmental features, such as type of recipe, and including the presence of a comonomer,e.g.up to 29% of styrene, have comparatively little effect on the relative amounts of vinyl,trans, andcisdouble bonds. (3) Differences in the physical properties of emulsion polymers of butadieneprepared at the same temperatureprobably must be attributed to differences in structure other than differences in the relative proportions of vinyl,trans, andcisdouble bonds, such as the average molecular weight, the molecular weight distribution, and the presence of a comonomer. It is shown that a maximum in the percentage of vinyl double bonds, previously indicated by experiment but attributed to gelation, is inherent to this system of three simultaneous competing modes of polymerizat

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110204

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110205

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractRecent experiments have indicated that the diffusion properties of a penetrant‐polymer system may change with time as diffusion proceeds. It is thought that two possible explanations of these time effects are slow changes of polymer structure accompanying diffusion and internal stresses exerted by one part of the polymer sheet on another as it swells. Two theoretical models are set up in order to express these effects quantitatively. The first model is essentially that in terms of which mechanical and other properties of polymers are commonly discussed, involving the concept of an instantaneous change of diffusion coefficient when the concentration changes, followed by a slow drift toward an equilibrium value. The second model expresses the effect of stresses set up between the outer swollen layers and the unattacked center of a polymer sheet during sorption. These stresses are slowly relieved as the diffusion proceeds, leading to a time‐dependent diffusion coefficient. The main features of diffusion behavior are established by calculation and the models are shown to account for the various types of sorption and desorption curves observed experimentally under different conditions,e.g., for sheets of different thicknesses and for different ranges of penetrant concentration. As examples, sorption and desorption curves calculated from the first model are shown to agree reasonably well with experimental curves for the methylene chloride‐polystyrene system. The rate of sorption and of the associated change in area of the sheet are accounted for by the second model. The presence of internal stresses also provides an explanation for the observation that there may be an appreciable interval of time during which a thin sheet takes up more penetrant than a thicker one under corresponding conditions. On the other hand, it is the slow structural changes which cause the rate of sorption to be not always inversely proportional to the square of the thickness of the sheet. It is concluded that both polymer relaxation and internal stresses play a part in determining diffusion behavior. The particular experimental results examined can be accounted for if the half‐life of the slow structural changes is comparable with that of the sorption experiment itself, and if the internal stresses change the diffusion coefficient by a factor of two o

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110206

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractSecond approximation methods for calculating distribution functions of mechanical relaxation times from complex dynamic data have been improved so that calculations of adequate accuracy can be made over a wider range of variables than was previously possible. Analogous methods for calculating distribution functions of mechanical retardation times and electrical relaxation times are given. The numerical values of the required second approximation correction factors are tabulated.

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110207

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110208

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractThe dielectric properties of polyvinyl isobutyral, hexanal, and 2‐ethylhexanal have been investigated. Dielectric constants and loss factors were measured at eight frequencies between 50 and 100,000 cycles in the temperature range of 25 to 130°C. Free energies, entropies, and enthalpies of activation were calculated, using the absolute reaction rate theory. The results illustrate the effects of “internal plasticization.” With increasing complexity of the interchain substituent, the electrical relaxation time is lowered, and the free energy, entropy, and enthalpy of dielectric relaxation are also decreased. These changes offer a quantitative measure of the decrease in interchain forces. It was also noted that the normal aldehyde substituents exhibited greater plasticizing action than the branched chain secondary groups. The electrical transition temperatures were compared with independently determined softening and inflection temperatures. The electrical and mechanical determinations were in good agreement for identical samples of the po

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110209

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110210

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY