摘要:

AbstractA model of polymeric materials has been developed that includes many of the features of condensed‐phase polymer chain dynamics, central among them chain relaxation via conformational motion. The model consists of a number of chains of particles that are connected by bonds with multiwelled potentials to approximate the energetics of conformational motion. Interactions between particles on adjacent chains are modeled by short range repulsive potentials. We have examined the stress‐strain behavior of the model using molecular dynamics simulations and find qualitative agreement with the observed experimental behavior of polymeric materi

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260701

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe local conformation and storage of energy in individual polymer chains during a deformation of a bulk polymer sample are examined by the computer simulation of a relatively simple model. It is shown that as the interaction between the chain atoms and surrounding medium increases, rotational angle motion is suppressed during the deformation, and large amounts of energy are stored in backbone bond angle and bond length distortions. The relationship of this phenomena toTgand the implications for chain relaxation are discussed.

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260702

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractPrimary nucleation of poly(vinylidene fluoride) (PVF2) γ‐phase crystals from the melt is affected by the presence of an electric field. Crystallization under the electric field is studied by polarized optical microscopy, thermal analysis, and wide‐angle x‐ray diffraction. Preliminary results indicate that the γ‐phase crystal nucleation rate and content are enhanced by the electric field.A modification of the classical theory of homogeneous nucleation of a crystalline phase is proposed to account for the experimental observations. Electrostatic interaction between the nucleus total polarization and the electric field contributes to the free energy of nucleation to a very large extent at low undercooling. Theoretical predictions indicate that a static electric field will increase the nucleation rate of a polar phase and will decrease the nucleation rate of a nonpolar phase. Confirmation of the former fact is observed exper

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260703

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is shown that ion‐ion interactions resulting from a proton transfer induce considerable miscibility in blends of functionalized poly(tetrafluoroethylene) with ethyl acrylate copolymers containing 4‐vinyl pyridine. Dynamic mechanical measurements, in conjunction with transparency of the samples, are used to evaluate miscibility. It is shown that mixing conditions exert a profound effect on the properties of the final blend. The glass transition of the blend is shown to be strong function of the blend composition, as is characteristic of highly miscible syst

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260704

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe dynamic mechanical relaxations of poly(trimethylene glycol terephthalate) (PTMT), poly(ditrimethylene glycol terephthalate) (PDTMT) and two copolymers obtained from them have been studied between − 150 and 200°C with a dynamic viscoelastometer. The four polymers show three relaxations that are designated α, β, and γ in order of decreasing temperature. The α relaxation is considered to be the glass transition of the polymers. The β relaxation is wider and weaker than the α, as normally occurs in the polyester series. The γ relaxation takes place at temperatures below − 100°C and is usually overlapped by the β relaxation. The influence of thermal and mechanical histories on the nature, location, and intensity of the three relaxations is studied

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260705

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractDilation of poly(vinyl benzoate) and poly(vinyl butyral) accompanying sorption of carbon dioxide is measured with a cathetometer under pressures up to 50 atm at 25°C. Sorption isotherms for carbon dioxide in these polymers were also determined gravimetrically. Each dilation isotherm plotted versus pressure, as well as the sorption isotherm, showed an inflection point corresponding to the glass transition of the polymer‐gas system. The dilation isotherms changed their form at that point from concave to convex to the pressure axis or to a straight line. Dilation and sorption isotherms exhibited time‐dependent hysteresis below the inflection point but not above the point. Partial molar volumes of carbon dioxide in polymers, which were determined from dilation and sorption data above the point, were found to be independent of concentration and larger than those below the point. The latter volumes depended on concentration. Based upon the extended dual‐mode sorption concept, which takes account of plasticization of polymer by sorbed gas, a dilation model was developed. Dilation data were described well by the

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260706

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe large direct current (d.c.) conductance observed at low frequencies and high temperatures in conjunction with a simple electrical circuit model was used to calculate specific conductivities in PVC and mixtures of PVC with a poly(ethylene‐vinyl acetate) copolymer. Activation energies for d.c. conduction and dipole relaxation in PVC and the blends were found to be in reasonable correspondence. The effects of different electrode materials on the d.c. conductance as well as on electrode polarization are discusse

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260707

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe polarized electronic spectrum of oriented poly(ethylene terephthalate) (PET) sheets was obtained from the specular reflection spectrum using the Kramers‐Kronig relationship. The surface orientation function of drawn and drawn/annealed PET sheets was determined from the dichroic ratio of the second π* ← π transition observed at 41,000 cm‐1. The bulk orientation functions in the crystalline and amorphous regions were evaluated from wide‐angle X‐ray diffraction and sonic modulus measurements. On annealing of drawn PET sheets, the crystalline orientation and crystallinity were much improved, but the amorphous orientation function showed a minor decrease. The overall molecular orientation in the surface of the drawn PET sheet was shown to be approximately equivalent to the molecular orientation

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260708

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractPoly(vinylidene fluoride) films were implanted with high‐energy (up to 6 MeV) He, C, O, and Ni ions and characterized using DSC, FTIR, and solubility measurements. None of the ions were energetic enough to penetrate the polymer film completely. The effects of ion energy, fluence, and ion type were studied individually. The implantation process lowered the crystallinity, induced crosslinking, and produced carbonyl groups on the polymer. The ion energy (in the range 0.4–4.5 MeV for He ions) had the most drastic effect, the radiation damage was found to increase with decreasing energy. The sample implanted with 0.4 MeV He ions lost 81% of its initial crystallinity and was only 24% soluble, even though the incident ions have a range of only 2.7 μm in this case. The other samples retained most of their initial crystallinity but still were substantially cross‐linked. The results can be qualitatively explained by assuming that hydrogen free radicals, produced during implantation, can diffuse throughout the sample and react, resulting in crystallinity and solubility losses beyond the ion deceleration

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260709

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractPolyester‐polyamide (PET/PA) copolymers offer a wide range of possible applications where both dimensional stability and good impact resistance can be achieved from their synergism. In order to ensure these properties for long‐term use, however, problems of phase separation, volume change, and chemical reequilibration on heating or aging must be identified and overcome. Wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), and thermal analysis were employed to follow the microstructure of a 70:30 PET/PA copolymer with several different processing histories as a function of heat history and both short‐term and long‐term aging. Heating the copolymer, as received, above the melting temperature of PET caused phase mixing. The effect of heating on crystallinity depended on starting crystallinity. Holding the copolymer at 50°C, just below the glass transition temperature of PET, caused phase separation in samples which had been annealed for 30 min at 150°C. On long‐term aging samples gave evidence of phase mixing. The results indicate highly nonequilibrium structure in the material, regardless of the

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260710

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY