摘要:

AbstractThe stress‐optical behaviour of an elastomeric network of poly(diethylene glycol terephthalate) (PDET) was measured over a wide range of elongation ratios α (up to 5) and temperatures (293‐353K). No evidence of strain ‐induced crystallization was found;on the contrary, the plot of birefringence versus stress exhibits negative deviations from linearity at values of α over 2.6. Values of the optical configuration parameter Δα of the order of 20 × 10−24cm3with relative temperature coefficients of ‐1.1 × 10−3K−1were found for the unswollen sample. The introduction of tricresylphosphate as diluent roughly doubles the birefringence of the network, presumably because of an increase in intermolecular interactions. Theoretical calculations carried out with the RIS model give values of Δα about one order of magnitude smaller than the experimental ones and temperature coefficients of about 4.1 × 10−3K−1. No reasonable modification of conformational energies or contributions to the anisotropic part of the polarizability tensor would achieve agreement between theory and experiments. The discrepancy between theoretical and experimental results may be qualitatively explained by i

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220601

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe transition of NMR properties from a solidlike spin system response to a liquidlike one observed on molten polymers or on concentrated solutions is analyzed to characterize the slow diffusion process of long linear polyisobutylene (PIB) chains. It is first shown that the relaxation function of the transverse magnetic component of protons linked to PIB chains obeys a superposition property when the polymer concentration is varied from 0.5 to 1.0g/cm3;this is interpreted as reflecting the applicability of the viscoelastic submolecule concept to the description of NMR properties. The transition in NMR properties is then analyzed numerically, using a model of polymer chain relaxation based on a multiple‐relaxation‐mode process analogous to the Rouse model. The terminal relaxation time τv1is shown to depend upon the chain molecular weightMasM3; it is found to be equal to 8.3 × 10−2s for molecular weightM= 2.25 × 105and concentrationc= 0.47 g/cm3in carbon disulfide at room tem

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220602

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe transverse magnetic relaxation of13Cαnuclei has been studied in concentrated solutions of polystyrene. The magnetic relaxation rate was measured as a function of molecular weight at several temperatures (313,318, and 323 K) and at several concentrations (0.53, 0.43, and 0.34 g/cm3). The spin‐system response of these nuclei in natural abundance exhibits a characteristic evolution from pseudosolid properties to liquidlike one, induced by decreasing the molecular weight of polymer molecules. This evolution is analogous to that already observed in protons attached to polyisobutylene or polydimethylsiloxane chains; it is assumed to be induced by an increase of the disentanglement rate of polymer chains. The spin‐system response may be considered as reflecting single‐chain magnetic properties, because of the low concentration of13CCαnuclei, although all chains are in dynamic interaction with one another. The NMR disentanglement transition is interpreted in terms of a two‐step motional averaging effect involving submolecules. A numerical analysis of NMR properties is given using a model of polymer chain relaxation based on a multiple‐mode relaxation process, characterized by (i)a terminal relaxation time τv1depending uponM3, the molecular weight, and approximately proportional to the polymer concentrationC(like the reptation time); (ii)a relaxation‐time spectrum analogous to a Rouse spectrum; (iii)a terminal relaxation time τv1= 2.5 × 10−2s forM= 2.5 × 105,C= 0.53 g/cm3in carbon tet

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220603

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA linear chain model is used to calculate the thermal expansivities of polymer crystals from room temperature down to liquid‐helium temperature. Because of restraint by strong covalent forces, vibrations along the chains give a negligible contribution. Vibrations transverse to the chains cause the length projected along the chain direction to decrease. The expansivity along the chain direction, αc∥is therefore negative, and has temperature dependence characterized by the low Debye temperature of transverse vibrations. These vibrations, through a cubic term in the interchain van der Waals potential, also cause a positive expansivity, αc⟂perpendicular to the chain direction. The theoretical predictions for αc∥and αc⟂agree quite well with experimental data over the wide temperature range under

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220604

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe lateral sizes of shish crystals crystallized from high‐molecular‐weight isotactic polystyrene and different blends with atactic polystyrene were examined with the help of transmission electron microscopy. It is found that the lateral sizes of shish crystals decrease with increasing content of the noncrystallizable aPS. A model accounting for the observation is propo

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220605

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe author refines and generalizes a model for diffusion in glassy polymers which he previously introduced. The model unifies many diverse observations by explicity formulating the common property of a glassy polymer in all its various modes, namely the finite relaxation time due to its slow response to changing conditions. An integral approximation method is used to study the motion of the penetrant front and the glass‐gel interface and a useful polynomial approximation method is introduced for use in special simple situation

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220606

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA series of polypropylene‐copolymer laminates produced by biaxial orientation in the 120–155°C range has been characterized by refractometry and infrared (IR) spectroscopy. The copolymer was a random ethylene‐propylene resin and the IR techniques included tilted‐film transmission as well as internal reflection, both using polarized radiation. The IR techniques yielded spectra corresponding to the machine, transverse, and through directions. Similarly, the refractometry gave refractive indices of both components of each laminate along all three axes. Results from the three techniques were compared and contrasted and the validity of the calculated internal reflectance spectra discussed. Practical methods to estimate the source and extent of errors in the latter technique from false radiation and contact problems were

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220607

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractSamples of isotactic polypropylene in the α form may have different degrees of order in the up and down positioning of the chains. By suitable programming of the crystallization history of unoriented samples it is possible to show, from DSC and WAXS data, that a strict correlation exists between the melting behavior and the degree of ordering of the chains. The process of ordering at annealing temperatures above 150°C may lead to a “continuum” of modifications of the α form from less ordered to highly ordered ones; correspondingly we observe an increase in the melting point by as much a

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220608

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAn interpolation model of density fluctuations in amorphous bulk polymers is suggested for the explanation of some peculiarities of structural relaxation of amorphous polymers volume. The main peculiarities of the model are (i) its account of the influence of fluctuations in the region where the WLF theory is true (the region of large fluctuations); (ii) its account of small fluctuations in the region where the dissipation mechanism appears to be considerably different from that in the region of large fluctuations; and (iii) its joining of the solutions of the resulting kinetic equations in the crossover region. On the basis of the suggested model we have obtained an equation of the Fokker‐Plank type for the distribution function for density fluctuations with nontrivial boundary conditions for large fluctuations, and a quasistatic solution for small ones. These equations are analyzed and numerically solved in the isothermal regime. The results show that the theory corresponds to the WLF theory at temperatures much higher thanTgand that memory effects are found in theTgregion. In addition, preliminary estimates show that nearTgan extreme form of temperature dependence on activation energy is observed. All these facts agree qualitatively with experimen

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220609

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractSorption isotherms for pure CO2and pure CH4in Kapton H® polymide films at 60°C are reported for pressures up to 20 atm and are analyzed in terms of the dual‐mode sorption model. An experimental scheme for the measurement of steady‐state permeabilities of both pure and mixed gas feeds is described. Permeabilities of Kapton to the individual components at 60°C are presented for a mixture comprised of 32.2% CO2in CH4as functions of feed pressure up to 590 psi (absolute). The permeabilities for the individual penetrants in the mixed feed are lower than the respective purecomponent values at the corresponding partial pressures. Furthermore, the permeabilities of both penetrants drop as the feed pressure is increased at constant composition. The dual‐mobility transport model used to analyze the data postulates that the observed pressure and composition dependence of the permeabilities is due to competition between penetrants for a limited microvoid sorption capacity in the glassy polymer. It is demonstrated that in addition to flux depressions due to dual‐mode effects, nonideality of the gas phase must be accounted for to explain the substantial flux depressions observed for the CO2/CH4mixtured used in

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220610

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY