摘要:

AbstractThermogravimetric and differential thermal analysis have been employed to study the thermal degradation patterns of poly‐m‐aminostyrenes and poly‐m‐acetamidostyrenes of different molecular weights and also the corresponding 2:1 copolymers with styrene. The thermal degradation routes have also been compared and contrasted with that of polystyrene. Experiments have been carried out in static air and dynamic nitrogen, and the different behavior exhibited by these polymers has been reconciled in terms of their differing structures and different mechanisms for pyrolytic degr

ISSN:0021-8995    

DOI:10.1002/app.1966.070100201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractEquilibrium pressure‐volume‐temperature behavior in both the solid and molten regtions was determined for a high density (ρ = 0.958 g./cm.3) polyethylene. Data were measured with a recently developed compressibility device capable of obtaining precise and accurate data. Residual curve treatment showed that the data were true equilibrium data. Compressibilities calculated from the data of this Work compared favorably to existing data which were limited to 205°C. The presented work extended the compressibility behavior to 250°C. It was also found that differences in compressibility of low and high density polyethylenes were not eliminated. in the molten region, indicating that the effect of differences in morphology was not eliminated. The Spencer‐Gilmore equation was fitted to the data of the present work. The internal pressure (π) term of the equation showed a definite relation to polymer m

ISSN:0021-8995    

DOI:10.1002/app.1966.070100202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractBy using a similar apparatus to that described by Baer and McLaughlin but differing in detail, the surface characteristics of samples of polyethylene, polypropylene, and a woven glass fiber/polyester laminate have been studied after periods of immersion in sulfuric acid at 60°C. Results show considerable progressive variation over the range of immersion times employed (up to 170 hr.), suggesting that surface changes might be considered as a measure of the corrosion involved. (No measure of the corrosion was attempted). The presence of a water layer on the surface of the test piece is suggested as being the reason for the plot of sin αsversus V‐2/3giving an intercept on the sin αsaxis whereas in the original work of Baer and McLaughlin the plot passes through the or

ISSN:0021-8995    

DOI:10.1002/app.1966.070100203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThe cure of heavily silver‐loaded epoxy resins with several amines has been investigated by resistivity–time measurements under isothermal conditions. For favorable cases activation energies in the range of 14–17 kcal./mole have been derived from slope analyses of the ρ−t plots. The relationship of the technique to similar measurements on unfilled or lightly loaded resins is discussed. Many aspects of the electrical behavior of silver‐based conductive adhesive systems are clarified by the ki

ISSN:0021-8995    

DOI:10.1002/app.1966.070100204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractStress softening of carbon black‐reinforced butadiene‐styrene rubber was studied as a function of the rate and temperature of the original tensile deformation. To a good approximation, stress softening depends on the product of the extension rate and a temperature function which is analytically well represented by the familiar Williams‐Landel‐Ferry relationship. When the elongation of the original deformation is also varied, a good correlation is obtained between stress softening and the maximum stress attained in the original extension, irrespective of the particular combination of strain, strain rate and temperature used to achieve this stress. Variables which tend to increase the stiffness of the vulcanizate, such as increased degree of crosslinking or carbon black chain structure, also increase stress softening; dilution by plasticizers decreases it. Prestressing at high strain rates and low temperatures affects the stress–strain curve of the softened vulcanizates beyond the elongation of the original extension. Connections are established between stress softening and viscoelastic and failure behavior. The evidence presented favors the contribution of several mechanisms to the general phenomenon of stress softening. These are thixotropy of transient filler structures, network chain rupture, and breakage of “permanent” filler structure. The latter appears to be most important at high strain rates, low temperatures, and with highly reticulated “st

ISSN:0021-8995    

DOI:10.1002/app.1966.070100205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractPolycarbonates of methyl, ethyl, n‐propyl, n‐butyl, and n‐hexyl 4,4‐bis(4‐hydroxyphenyl)pentanoate and copolycarbonates with bisphenol‐A of 0.5‐0.9 intrinsic viscosity in dioxane were prepared by a homogeneous CH2Cl2pyridine method and the physical properties determined. Increasing the number of carbon atoms in the DPA ester alcohol group from 1 to 6 decreased the initial softening temperature of the polycarbonates from 126 to 58°C. ; this change also increased the solubility of the polycarbonates in aromatic solvents and in three ketone solvents. O2transmission rates were not affected by increasing the ester chain length. CO2transmission rates increased as DPA ester alcohol chain length increased. Methyl DPA polycarbonate had the highest tensile strength and per cent elongation and the lowest O2and CO2tr

ISSN:0021-8995    

DOI:10.1002/app.1966.070100206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractChanges in the molecular weight distribution of natural rubber, after mill mastication, have been studied by using a Water's gel permeation chromatography. This study indicates that as the polymer is milled the distribution is narrowed primarily through the breaking down of large molecular weight molecules. The peak of the distribution curve shifts to lower and lower molecular weight with increased milling time but it appears to be approaching a limiting molecular weight after 76 min. of milling time. One unexpected result is the development of a secondary hump in the distribution curve at the high molecular weight end. This hump gets larger and moves to lower molecular weight with increasing milling time until 76 min. of milling, at which time it disappears entirely.

ISSN:0021-8995    

DOI:10.1002/app.1966.070100207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractIn order to study structure‐tissue reactivity relationships and ultimately develop a less necrotizing adhesive, this laboratory undertook a study of the synthesis and degradation of the homologous series of α‐cyanoacrylate monomers and polymers. A method for synthesizing high purity cyanoacrylates and some of their chemical and physical properties and presented.In vitrokinetics studies under heterotgeneous and homogeneous conditions indicate that cyanoacrylate polymers degrade by hydrolytic scission of the polymer chain. The products resulting from such a scission are formaldehyde (positively identified by derivative formation) and ultimately and alkyl cyanoacetate. As the homologous series is ascended, the rate of degradation under neutral conditions decreases. In homogeneous solutions, under alkaline conditions, the ràte of degradation is considerably higher than under neutral conditions and the rates obtained with the methyl to the butyl derivative are of the same order. Aproposed mechanism of degradation is presented. Medical evaluation has indicated that as the homologous series is ascended, the greater the tissue tolerance to the monomers and polymers. The relevance of the results of the in vitro studies to this medical finding is pres

ISSN:0021-8995    

DOI:10.1002/app.1966.070100208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractLiquid carboxyl‐terminated polybutadiene (CTPB) on aging in air increased in viscosity and molecular weight and eventually gelled. Simultaneously, the acid content decreased without formation of anhydride, the changes being a function of the hydrocarbon portion of the molecule. Cured stocks of CTPB underwent changes on heating in air which were largely resinification due to oxidation. However, chain scission or hydrolysis also occurred, resulting in reversion of cure which could be observed in vacuum‐aged material or in the interior of the stocks. Commercial resins were compared, and a difference noted between CTPB prepared by ionic and free‐radical methods. The idea was presented that the greatest depth of oxidation was determined by the plane benetath the surface where the rate of oxidation equalled the rate of arrival of oxygen by diffusion. This idea was devloped mathematically from Fick's diffusion law and an equation derived which related the depth of oxidation to the temperature, the energies of activation for reaction and diffusion, and the rate constants for reaction and diffusion. By using the equation, relative rates of oxidation were determined and the energy of activation for diffusion of oxygen in CTPB was found to be 13.6 kcal.

ISSN:0021-8995    

DOI:10.1002/app.1966.070100209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThis investigation showed, as did an earlier investigation, that the adhesives tested exhibit greater resistance to rapidly applied stresses than they do to slower or gradually applied stresses. Also, the adhesives were shown to lose strength with test temperature whether tested rapidly or slowly. Within a region bounded approximately by a high‐temperature second‐order transition point (the ASTM heat distortion temperature) and a low‐temperature second‐order transition point, the test data fits an Arrhenius‐type exponential equation, S = AeE/RT, where S is the stress in the joint at failure and the other terms have their usual significance. Energies calculated from this expression are lower for dynamic (fast) than for static (slower) rates of testing. Further, it was shown that little change in bond strength occurs until time to failure is below 100 msec. Plots of stress versus 1/T for a series of test times show a decided discontinuity at 1/T = 0.0039

ISSN:0021-8995    

DOI:10.1002/app.1966.070100210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY