摘要:

AbstractA new method is suggested for the experimental determination of the dependence of the relaxation times on the temperature in dielectrics for which the time–temperature superposition principle is valid. The method makes possible the determination of this dependence for a separate relaxation process (for instance, for the β‐relaxation process) over a wide temperature range by means of comparatively simple mathematical operations which are only slightly sensitive to experimental errors. Two or more discharge‐current curves, measured with temperatures increasing in an arbitrary way with time, are used for this p

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130801

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe small‐angle x‐ray scattering (SAXS) from glassy poly(methyl methacrylate) has been measured using a Bonse–Hart system. The data cover the angular range (2θ) between 20 sec and 2 deg. After correcting for absorption, background, and beam divergence, the data have been placed on an absolute basis by comparison with the scattering from a standard silica suspension. The corrected absolute intensity decreases strongly with increasing angle over the range between 20 sec and 30 min, and is nearly constant between 30 min and 2 deg. The magnitude of the scattering in the constant range, 0.6 (electrons)2Å−3, is within a factor of 1.5 of the value predicted by the thermodynamic fluctuation theory for fluids applied at the glass transition temperature. The increase in intensity at smaller angles cannot be described by structures on the scale of the nodules reported in highly isotactic PMMA (150–200 Å), but can be well represented by small concentrations of heterogeneities, several thousand angstrom units in size, superimposed on the thermal density fluctuations frozen‐in at the glass transition. The bulk structure of this material is well described as a random amorphous solid, containing simple thermal fluctuations and a small concentration of relatively large h

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130802

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe dielectric constant of solutions of poly(γ‐benzyl‐L‐glutamate) (PBLG) in dichloromethane shows a jump near 195°K, irrespective of frequency. Therefore, the discontinuity is not a dispersion phenomenon but a phase transition in the thermodynamic sense. The transition temperature is independent of the concentration in the range from 0.01 to 10% by weight, but it increases linearly with the logarithm of the molecular weight of PBLG. The height of the jump depends strongly on frequency, concentration, and molecular weight. The viscosity also changes abruptly at 195°K. These results suggest that the PBLG molecule forms a cluster like a liquid crystal or is in a random coil state below the transiti

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130803

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractRecent work has shown that so‐called chain‐extended crystallization of polyethylene is crystallization of the newly discovered hexagonal phase. This hypothesis is supported by experiments on the pressure quenching of molten polyethyl

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130804

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractHeats of mixing of methanol with butyl isobutyrate and with oligomers of butyl methacrylate (monomer to tetramer) having a butoxyl group on one chain end have been measured. To discuss the effect of hydrogen bonding on the heat values, it is appropriate to correlate the heat per mole of binding sites with the binding site fraction. This dependence can be described by a single curve for all oligomers studied, in contrast to the results obtained in a previous paper for the same oligomers with chloroform. This fact suggests that the binding parameters for methanol are not influenced by the degree of polymerization.

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130805

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe micromechanism of tensile deformation of poly[p‐(2‐hydroxyethoxy)benzoic acid] fibers is discussed on the basis of a detailed esr study of radical formation. The concentration of primary phenoxy radicals, which were detected during deformation at room temperature as a direct indicator of main‐chain rupture, was determined by extrapolating the radical decay curves at various strains to zero time. The relation between the initial radical concentration and the strain is well expressed by the cumulative normal distribution curve. By use of this relation and a model of fiber structure, the distribution of the contour length of tie chains was determined. No radicals were detected during a second stretching cycle until the maximum strain in the first run was exceeded. The deformation model which includes alternating crystalline and amorphous regions connected by tie chains, a distribution of contour lengths of tie chains, and a phase transformation of molecular chains in the crystalline region accounted fairly well for the observed stress–strain behavior of monofilaments in first and second stretching cycles. The comparison between the observed and the calculated radical concentration suggests that statistical factors and other deformation mechanisms have to be taken into

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130806

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractLow molecular weight PVC polymers of known degree of crystallinity (44% by x‐ray diffraction), prepared in the presence of the chain‐transfer agentsn‐butyraldehyde andn‐butyl mercaptan, are examined by differential scanning calorimetry in order to ascertain temperatures and heats of fusion. Initial thermal scans are accompanied by large endotherms and appreciable weight losses due to the lability of the terminal groups originating from the chain‐transfer agents. However, further successive scans result in approximately invariant endotherms attributable to crystalline fusion. The maximum melting point, about 265°C, exceeds the value for commercial PVC, about 210°C, but is lower than a value deduced for a hypothetical completely syndiotactic polymer, about 400°C. The average heat of fusion ΔHuis 1180 ± 90 cal/mole, and the resultant entropy of fusion is 1.1 cal/deg/bond. The present ΔHuvalue differs significantly from previously reported values of 660–785 and 2700 cal/mole, based on melting point depression theory, but appears to be concordant with known heats for a series

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130807

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe morphology of crystalline end‐block copolymers of poly(thiacyclobutane‐b‐isoprene‐b‐thiacyclobutane) (TCB–I–TCB) was studied by optical microscopy, electron microscopy, and small‐angle x‐ray scattering (SAXS). A spherulitic texture was observed for both the TCB homopolymer and the TCB–I–TCB block copolymers. Well‐defined phases arranged in an ordered structure exist when the films are cast above the melting temperature of the crystalline end blocks. The dimensions and the arrangements of the domains have been derived from both SAXS and electron microscope measurements. The deformation mechanism of the 41% end‐block copolymer sample was also examined by a combination of SAXS and stress–strain studies. It was found that the interdomain spacing increased along the stretching direction as the extension ratio was increased. The morphology changes from hexagonally packed cylinders to rowtype cylinders upo

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130808

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractStrain‐dependent relaxation moduliG(t,s) were measured for polystyrene solutions in diethyl phthalate with a relaxometer of the cone‐and‐plate type. Ranges of molecular weightMand concentrationcwere from 1.23 × 106to 7.62 × 106and 0.112 to 0.329 g/cm3. Measurements were performed at various magnitudes of shearsranging from 0.055 to 27.2. The relaxation modulusG(t,s) always decreased with increasingsand the relative amount of decrease (i.e.,–log[G(t,s)/G(t,0)]) increased astincreased. However, the detailed strain dependences ofG(t,s) could be classified into two types according to theMandcof the solution. WhencM106, the curves were still convex and S‐shaped at very small and larges, respectively, but in a certain range ofs(approximately 3

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130809

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe steady shear viscosity η(k) and the stress decay function\documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \eta \left({t,k} \right)$\end{document}(the shear stress divided by the rate of shearkafter cessation of steady shear flow) were measured for concentrated solutions of polystyrene in diethyl phthalate. Ranges of molecular weightMand concentrationcwere 7.10 × 105to 7.62 × 106and 0.112–0.329 g/cm3, respectively. Measurements were performed with a rheometer of the cone‐and‐plate type in the range 10−4

ISSN:0098-1273    

DOI:10.1002/pol.1975.180130810

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY