摘要:

AbstractThe finite deformation elasticity of gels of stiff rodlike polymer chains is discussed theoretically. Unlike a rubber composed of flexible polymer chains, the elasticity of this system is energetic, and arises from the elastic deformation of the stiff chains which are forced to bend under macroscopic strain. The stress‐strain curve of this system is shown to be nonlinear even if the bending of the rods is small, and has a characteristic S‐shaped form which is unlike that of a rubber. The effect of orientational order is also discus

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180301

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe influence of temperature, frequency, and straight‐chain‐length distribution on the low‐frequency Raman‐active longitudinal‐acoustical‐mode (LAM) bands of polymers is discussed. Specifically, the effect of these factors on the intensity of LAM‐1, on the ratio of intensities of LAM‐1 to LAM‐k, and on peak position is computed or estimated. Band halfwidth and chain‐length‐distribution halfwidth are found not to be simply related. It is shown that the integrated intensity of LAM‐1 is very nearly proportional to the total le

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180302

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe tensile properties of bothcis‐ andtrans‐polyacetylene, (CH)x, were investigated in order to determine the variables that influence that ultimate extension ratio (l/l0) of polyacetylene films. It was found that whencis‐films of polyacetylene were extended in an inert (argon) atmosphere, ultimate extension ratios as high as 3.3 were obtained and with subsequent isomerization at 160–200°C under stress, a finall/l0, of about 4 was obtained. The extension ratio is extremely sensitive to exposure to oxygen and decreases markedly after periods as short as 1 min. It appears as though crosslinking may occur in the polymer when it is exposed to air and this produces brittleness in the specimen. When (CH)xwas isomerized fromcistotrans, it became brittle, even in the absenc

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180303

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractNeedlelike crystals of a phenylsilicon compound synthesized on crystallization during polymerization in a transport reaction in a temperature gradient, which were thought earlier to be polymeric diphenylsilylene, are shown to be actually tetraphenylsilane. Similarly produced crystals of the germanium analog led, in contrast, to polydiphenylgermylene. An overall reaction scheme uniting both reactions is suggested.

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180304

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractHeat capacities of liquid selenium have been measured by computer interfaced differential scanning calorimetry in the metastable region with an accuracy of ± 1% from 330 to 520°K. To avoid crystallization, the measurements were done on cooling. A semiquantitative fitting of the heat capacity to vibrational energy contributions, free volume (hole) effects, and heats of reaction from the changes in the ring‐chain and depolymerization equilibria was possible to within ±5% of the newly measured and literature data between the glass transition temperature (ca. 303°K) and 1000°K. It could be established that the shift in the ring‐chain equilibrium is not the major reason for the overall decrease in heat capacity above the glass transition temperature. The floor temperature, which was earlier placed at about 356°K, is possibly below the glass transition temperature. The increase in heat capacity beyond 800°K has been linked with the depolymerizatio

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180305

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractExcimer formation has been studied in a series of ancenaphthylene—methyl methacrylate copolymers of content varying over the total composition range. In accord with a previous model [Reid and Soutar,J. Polym. Sci. Polym. Lett. Ed.,15, 153 (1977)], the excimer formation has been described by a composite function representative of energy migration and excimer site concentration. In tramolecular energy migration in glassy solutions of the polymers was characterized by use of fluorescence depolarization measurements. The extent of energy migration in the acenaphthylene copolymers is determined by the mole fraction of aromatic chromophorefa. A function Σ descriptive of the excimer site concentration has been generated on the assumption that excimer formation results predominantly from next‐ to nearest‐neighbor interactions. Σ is based upon the pentad distribution of aromatic chromophores in the chain and contains pentad fractions appropriately weighted according to the frequency and relative importance of their potential excimer sites. Reactivity ratios of acenaphthylene and methyl methacrylate in copolymerization at 70°C werera= 0.80 and

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180306

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractProton spin‐lattice relaxation experiments on thebis‐(p‐toluenesulfonate) of 2,4‐hexadiyne‐1,6‐diol (TSHD) as a function of temperature (25 to 353 K), of frequency (22 and 44 MHz), and of conversion to polymer were performed to determine the molecular motions in this crystal and to follow the conversion via the changes in the relaxation timeT1. It was found thatT1is dominated below 125 K by weakly hindered (ΔE= 2.8 kJ/mole) tunneling (Λ = 220 MHz) CH3groups, at about 160 K by order‐disorder fluctuations around the phase‐transition temperature ϑcwhich depends strongly on the conversion, and above 200 K by the motion of the whole side group.T1can be used as sensitive probe for the conversion: The change inT1at about 44 K is directly proportional to the conversion, whereas the change at high temperatures (e.g., 353 K) occurs essentially at low conversions (⩽10%). This is explained by distorted (stressed) areas around the isolated polymer chains, which are estimated to be about 16 times the size of the chains. After an induction period the stresses are relieved by fu

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180307

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractEthyl acrylate ionomers were studied by stress relaxation. The results are compared with those for the styrene ionomers studied previously. The behaviour of the two systems is qualitatively similar, although significant quantitative differences exist. Specifically, the onset of thermorheological complexity is found here at 12–16 mole% of ions, while in styrene it is observed at ca. 6 mole%. Furthermore, the modulus‐temperature plots show great similarity if the present samples are compared with the styrenes containing about half as many ions. Other properties show similar trends. The increased dielectric constant of the acrylates is believed to be responsible for the observed differences in the two systems. The effect of a change in counterions was also studied to some extent. The onset of thermorheological complexity is seen to be qualitatively related to the size and charge of the cat

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180308

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe influence of molecular weight and temperature on the tensile drawing behavior of polypropylene has been studied, with particular reference to the production of ultra‐high‐modulus oriented materials. It has been shown that the optimum draw temperature is molecular weight independent to a good approximation, and that high‐modulus products can be obtained forM̄win the range 180,000–400,000, the highest modulus being achieved for polymer withM̄w= 181,000. As in the case of linear polyethylene, under optimum drawing conditions the Young's modulus relates only to the draw ratio. Low‐temperature moduli as high as 25–27 GPa were recorded, which compare favorably with a previously reported value of 42 GPa for the crystal‐lattice modulus. Although the drawing behaviour of the samples studied appeared comparatively insensitive to molecular weight, some of the properties of the draw materials, notably melting point and shrinkage at high temperature, showed a wide ra

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180309

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractWhen certain substances, notably waxes, are incorporated into rubber during vulcanization, the surface of the vulcanized rubber may subsequently become covered by a film of the substance diffusing out. This phenomenon, known as blooming, depends on the substance being soluble at the vulcanization temperature but only partially soluble at the temperature of blooming. A study has been made using pure waxes in natural rubber vulcanizates with a range of crosslink densities. The mass of bloomed material has been determined as a function of time, and the expected dependence on the square root of the time has been found to hold over the anticipated range. It has been shown that the kinetics of the process cannot be explained simply in terms of the degree of supersaturation of the wax in the rubber, the observed rates being much too low. This appears to be related to the precipitation of the wax in the body of the material. A theory has been developed based on a calculation of the stresses set up around such a precipitated particle and the effect of the consequent free‐energy gradient on the rate of diffusion. Comparison with experiment shows satisfactory agreement with the theor

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180310

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY