摘要:

AbstractSpecific heats of plasticized poly(vinyl chloride) can be readily obtained by means of the thin foil calorimeter when the polymer is fabricated into sheet or film. The effects of temperature and plasticizer content on the specific heat and of the plasticizer content on the glass temperature are readily observed. The data may be used to estimate the glass temperatures of plasticizers where those temperatures are not readily reached by normal techniques. The specific heat at the glass temperature is approximately 0.255 for the ranges of 0–30 phr plasticizer. A definite glass transition is not observed with 60 phr plasticizer. No other transitions were observed between 200 and 400°K. The previous history of the polymer is important, as it can change the specific heat of the polymer noticeably, especially above the glass temperature. Comparison of the values listed here with those obtained by others should be made with the understanding that these samples were fabricated by extrusion and were free of observable strain. The degree of crystallinity of these polymers is very small, probably less than 10%, since none was found by x‐ray diffraction. The plasticizing effect of some stabilizers was n

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040501

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractThe ability of various polymers to acquire persistent polarization (i.e., to become electrets) was investigated. Polarization was induced in the polymers by two methods: (a) by cooling under a voltage drop and (b) by cooling with flow under pressure. There was found to be an optimum temperature for electret formation by either method. This optimum temperature was roughly 37°C. aboveTgwhen polarization was produced by application of a voltage drop and roughly 57°C. when polarization was produced by flow under pressure. Crystallinity and the nonhomogeneities present in blended polymers were harmful to electret formation, but a small critical amount of ionic impurity was helpfu

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040502

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractDepolarization currents were used to study the persistent polarization induced in polystyrene and poly(methyl methacrylate) by cooling with flow under pressure. These studies showed that the charge on electrets made by flow under pressure consists in part of a surface charge which leaks off rapidly in moist air and in part of a charge due to volume polarization which decays more slowly. The volume polymerization produced in poly(methyl methacrylate) by flow under pressure is of the same order as that produced by cooling under a voltage drop, but flow under pressure produces a larger surface charge.

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040503

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractThe determinations of the number‐average molecular weight of polyethylene by cryoscopy has been improved, permitting precise measurements with both linear and branched polyethylenes in the molecular weight range 4,000–30,000. Improvements include a cryometer of new design, a lower‐melting cryoscopic solvent containing a nucleating agent to control supercooling and rate of crystallization of the solvent, and more precise measurement of freezing point depression. Polyethylene samples are dissolved in hexamethylbenzene admixed with 0.1% of cadmium iodide, and steady‐state freezingpoint depressions are measured with a thermistor to a maximum sensitivity of 5 × 10−5°C. Molecular weight measurements are reproducible to within ±10%. The cryoscopic apparatus and procedure are described in detail, and results obtained with samples of linear and branched polyethylene are presented a

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040504

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractCrystallization kinetics of crystalline fractions of propylene oxide polymers made with different catalysts have been studied by isothermal dilatometric and microscopical measurements. Isothermal microscopical measurements indicate that spherulite growth in these polymers proceeds from predetermined nuclei. The half time for spherulitic appearance is less than, but of the same order as, the half time for complete crystallization. Only by taking this factor into account can the dilatometric data be represented by the Avrami equation. The deviation of the crystallization isotherm from that predicted from the microscopical data using the Avrami theory is attributed to a secondary crystallization process taking place within the spherulite. Crystallization continues long after spherulites completely occupy the available volume in the polymer. By assuming that the secondary crystallization proceeds as a first‐order process in the uncrystallized, but crystallizable, portions of the melt, it is shown that the crystallization isotherms can be completely described in terms of four parameters. These are: (1) the time constant for the primary crystallization process; (2) the time constant for nucleation; (3) the time constant for the secondary crystallization process, and (4) the extent of secondary crystallization. The important conclusions of these studies are: the rates of nucleation and of spherulitic growth are far more dependent on temperature than on stereoregularity; the ratio of the rate of the secondary crystallization process to that of the primary crystallization process is almost independent of temperature, but increases with increasing stereoregularity of the polyme

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040505

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractGel permeation chromatography is an elution chromatographic process depending on the permeation of the solute through a bed of gel particles. This process is used in the estimation of molecular weight distributions of polymers, since elution occurs in decreasing order of molecular size. The eluting species, however, are not perfectly fractionated, and apparent broadening of the distribution occurs. This broadening results from an axial (longitudinal) mixing of the eluting species. Consideration of the accessible bed volume for each species permits a correction to be made for this axial dispersion. The concept was applied to heterodisperse distributions by solving the resulting simultaneous equations. A least‐squares regression may be employed to utilize the experimental data most effectively. The experimental chromatogram can be described in terms of accessible bed volume and dispersion coefficient of each species together with flow rate, sample concentration, and chromatograph column geometry. The chromatogram corrected for the axial dispersion describes the molecular weight distribution more accurately than does the experimentally determined curve. The correction procedure was applied to a well‐characterized polystyrene; the results of the gel permeation chromatography show excellent confirmation of the results of fractionation and of other instrumental analy

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040506

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractTorsional creep measurements on four natural rubber vulcanizates, crosslinked to different degrees, were carried out in the temperature range from −50 to 90°C. This investigation complements the studies on identical samples of the stress relaxation behavior by Chasset and Thirion and of the dynamic mechanical response by Ferry, Mancke, Maekawa, Ōyanagi, and Dickie. The creep measurements reported are shown to be in agreement with the stress relaxation results. In addition to the usual temperature reduction, a superposed curve was obtained for the long time response using the apparent molecular weight between crosslinks,Mc, as a reduction variable. The variation in viscoelastic response with crosslink density is interpreted as a restrictive action of the chemical crosslinks on the transient entanglement netw

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040507

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractThe behavior of films of polyelectrolytes at the water‐organic liquid interface depends on the nature of the interface and the pH of the substratum. The present paper investigates the influence of these two factors on the cohesive forces between monomer units. Two polyelectrolytes were studied: poly(methacrylic acid) (APM) and poly‐2‐vinylpyridine (2‐PVP). In the case of uncharged films, the collapse pressure decreases when the polarity of the organic phase becomes more important, whereas the term ω/kT, which appears in the theory of Motomura and Matuura, increases. A quantitative relation between the parameter ω/kTand the collapse pressure may be deduced. The behavior of the ionized surface film at different pH values is modified by the choice of the interface. However, there exists a competition between two phenomena: the dissolution of ionized residues in the substratum and the electrostatic repulsion between charges in the surface plane. Depending upon whether the first or the second parameter is more important, we observed that the surface pressure decreased or increased with the degree of i

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040508

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractThe structure of polypropylene crystallized at pressures up to 5000 atm. has been studied. Upon slow cooling from the melt at 320 atm., the γ modification, previously found only in low molecular weight and stereoblock fractions, begins to appear in small amounts in addition to the normal α monoclinic form. As the pressure is increased further, a larger proportion of the sample crystallizes in the γ form until, at 5000 atm., only the γ modification is present. X‐ray and DTA studies show that the γ form of polypropylene transforms to the normal α modification at a temperature only slightly below the γ melting point. Evidence is presented which favors the occurrence of a solid‐state transition as a model of transformation to the α form. Results from isothermal crystallizations at low supercoolings and annealing experiments under high pressure show that the melting point of the γ modification of polypropylene is very sensitive to crystallit

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040509

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractMechanical damping measurements were carried out in the range of 103–105cps and between 60°K. and the softening point on some substituted Polystyrenes and poly(vinyl benzoates) containing different substituents (methyl groups, methoxy groups, and halogen atoms) either in the ring or in the main chain. Theorthoandmetaring‐substituted polystyrenes do not show any secondary mechanical relaxation in the glassy state, although all the other substituted polystyrenes, exhibit a low‐temperature damping peak (δ process) (which is in some way connected with ring motions) whose height and temperature location depend on nature, position, and number of substituents. Substituents in theparaposition of the ring or in the α position in the backbone chain shift the δ peak of the unsubstituted polystyrene towards higher temperatures; this shift is accompanied by an increase of the apparent activation energyE*. Substitution in the β position, on the contrary, does not affect the δ peak. Analogous results are obtained for substituted poly(vinyl benzoates), which exhibit, in addition, a β relaxation effect, associated with carboxyl group motions. A very good correlation is found between the values ofE* and the limiting relaxation time τ for the δ relaxation of polystyrenes and poly(vinyl benzoates), similarly substituted in the ring, indicating that the δ relaxation leads to absorption curves in the mechanical relaxation spectrum which are characteristic of the structure of the arom

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040510

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY