摘要:

The melting of nascent superhigh-molecular-weight poly(ethylene oxide) (PEO) has been studied by means of differential scanning calorimetry (DSC). High values of the melting temperatures and enthalpies were established. The higher temperatures are explained by the presence of tie molecules in high concentration. The phase transition is accompanied with the absorption of heat in addition to the heat of fusion. This additional heat can be interpreted as follows: (1) a large entropy change in amorphous areas during the transition, caused by disorientation of chains with a long distance between the chain ends in the nascent crystal state, to entangled statistical coils; and/or (2) a large internal energy change in the crystal areas caused by deformation of the crystal lattice under the action of internal stresses, increasing with temperature in the range from solid-plastic crystal transition (50°C) temperature to the melting point.

ISSN:0022-2348    

DOI:10.1080/00222348208018787

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The influence of the physical network of entangled molecules in molten, superhigh-molecular-weight poly(ethylene oxide) (PEO) on the formation and morphology of the crystals is described based on light and scanning electron microscopy, small-angle light scattering, and wide-angle X-ray diffraction. The morphology depends on the degree of the flow of the polymer melt. The flow is a temperature- and time-dependent process. Different spherulite like formations are formed. They are built from lamellae with [401] fold surfaces. The perfection of the crystallites also depends on the degree of flow.

ISSN:0022-2348    

DOI:10.1080/00222348208018788

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The melting of superhigh-molecular weight poly(ethylene oxide) (PEO) previously annealed or thermally treated in he molten state was studied by means of differential scanning microcalorimetry. An approach for clarification of the thermal balance of the complicated melting process is made.

ISSN:0022-2348    

DOI:10.1080/00222348208018789

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The phase composition of nascent and thermally pretreated superhigh-molecular-weight polyethylene are investigated at stepwise increased temperature by means of wide-angle X-ray diffraction. In addition to the usual dominating orthorhombic lattice, a monoclinic and several lattices with hexagonal symmetry are observed. The intensity of the additional reflexes changes with temperature below and above the melting point of the orthorhombic lattice. These peculiarities of the phase composition are explained through the existence of strong stresses applied on the crystallites, caused by strained tie molecules with high concentration in the nascent sample.

ISSN:0022-2348    

DOI:10.1080/00222348208018790

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The piezoelectric coefficient of commercial polyvinylidene fluoride piezoelectric film was found to decrease with increasing preload due to a stress-dependent modulus; preload had no effect on the pyroelectric coefficient, in keeping with current theory. Both coefficients demonstrated an irreversible rise on heating due to amorphous phase depolarization at the Tg, near 80°C in this highly oriented material, following which these values were temperature-independent in the range 20–100°C.

ISSN:0022-2348    

DOI:10.1080/00222348208018791

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The effects of solidification pressure and cooling rate on the as-prepared density of polystyrene have been determined simultaneously. In general, the dependence of density individually on vitrification pressure and cooling rate is as previously reported; i.e., density decreases with increasing cooling rate and increases in a logarithmic fashion with pressure. However, we observe that the variation of density with vitrification pressure (∂p ρ/∂Pv) is independent of cooling rate; that the variation of density with vitrification cooling rate (∂ρ/∂Rv) is independent of pressure; and that the as-prepared density varies linearly with log(vitrification cooling rate).

ISSN:0022-2348    

DOI:10.1080/00222348208018792

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The Adam and Gibbs (AG) theory which describes the cooperative relaxation phenomena in the main transition region in terms of the configurational entropy of the system has been extended to describe also the dependence of both the relaxation times and the glass transition temperature Tgon the external pressure P. The resulting relations contain quantities accessible both by thermo-dynamic (discontinuities in the isobaric heat capacity and in the thermal expansion coefficient) and by viscoelastic (parameters of the temperature dependence of relaxation times) measurements. Theoretical relations adequately describe pressure experimental data on polystyrene, poly(vinyl acetate), and poly(vinyl chloride). The expression dTg/dP derived from the AG theory is at variance with Ehrenfest's relation; the connection between the AG theory and the order parameter description of the glass transition is discussed.

ISSN:0022-2348    

DOI:10.1080/00222348208018793

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

During deformation of glassy amorphous polymers the rotation of rigid chain segments around skeletal bonds is restricted simultaneously by configurational (intramolecular) and chain-chain (intermolecular) energy barriers. These barriers are modeled in a self-consistent manner for six polymers by use of an approximate analytical treatment. The comparative contribution of these barriers to the small-strain modulus of the bulk solid is used as a basis for distinguishing between two mechanisms of stiffening. With polycarbonate, polyphenylene oxide, and an aromatic polyimide, in which the rigid chain segment is relatively long, the modulus derives its value primarily from the resistance to displacements across chains due to intermolecular barriers. With vinyl polymers such as polystyrene, poly(vinyl chloride) and poly(methyl methacrylate), however, in which the rigid chain segment is short, resistance to displacements along the main chain due to intramolecular barriers contributes equally significantly to the modulus. Our calculations also show that the length of the rigid chain segment, acting as a mechanical moment arm, affects the resistance to intramolecular displacements much more than does the height of the rotational energy barrier.

ISSN:0022-2348    

DOI:10.1080/00222348208018794

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Accurate measurements of the depolarized Rayleigh-Brillouin light scattering spectrum have been made on pure styrene as it thermally polymerizes. The ratio of the depolarized scattering per unit volume of the monomer to that of the polymer is observed to be constant as polymerization proceeds; the value of this ratio was determined to be 2.61 ± 0.06.

ISSN:0022-2348    

DOI:10.1080/00222348208018795

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor