摘要:

The complementary dynamic mechanical and dielectric methods have been extensively employed in the characterization of organic polymers. While the former method is sensitive to molecular motions that affect the mechanical properties, the latter has the advantage of detecting molecular motions that involve dipole oscillation. We have used both methods simultaneously within this study in order to help understand a portion of the molecular transitions that occur within a series of synthetic polypeptides.

ISSN:0022-2348    

DOI:10.1080/00222347408204545

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Morphological factors exerting an effect on thermomechanical analyses of crystalline polymers are discussed for three kinds of samples with quite different morphologies. (1) Bulk-crystallized linear polyethylene (PE) with spherulitic structure shows an a absorption, which was shown to be composed of two absorptions, α1and α2. Based on the super-structural characterization and viscoelastic behavior of a single crystal mat of PE, the α1absorption was assigned to the deformation associated with mosaic block boundaries and the α2absorption to the uniform shear deformation of lamellar crystals. (2) Highly oriented and well crystallized poly-[p-(2-hydroxyethoxy)benzoic acid] shows the α → β crystal transformation caused by drawing stress. The role of tie links translating the stress along the fiber axis was proved by calculating the mechanical dispersion behavior of the dynamic modulus based on the super-structural parameters. (3) Oriented crystallites of PE prepared from dilute solution with a shish-kebab morphology shows outstanding thermal stability in comparison with lamellar crystals as found in melt-spun and drawn fibers and solid-state extrudates of PE. The TMA data were compared with DSC thermograms.

ISSN:0022-2348    

DOI:10.1080/00222347408204546

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The compression behavior of some rubberlike networks in equilibrium and non-equilibrium conditions has been investigated. The experimental data clearly indicate that non-equilibrium components are operative on the compression modulus value. Results are interpreted in terms of supramolecular order in the amorphous materials.

ISSN:0022-2348    

DOI:10.1080/00222347408204547

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Physical crosslinking of urethane elastomers is essentially based on statistical systems of hydrogen bonds within the hard segment domains. Two dimensional models of these systems, given in previous papers, are now replaced by three-dimensional models in the case of butane diol and pentane diol extenders, respectively. A suggestion is made for the transverse crosslinking mechanism with diamine extenders. Taking into account the conditions for three-dimensional hydrogen bonded systems a correlation between the cross-linking structure and heat-distortion temperature of diamine and diol extended elastomers is obtained.

ISSN:0022-2348    

DOI:10.1080/00222347408204548

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The quantitative description of small-angle X-ray scattering curves (SAXS) of copolymers of ethylene needs the determination of a number of structure parameters. The number of parameters, which are due to a certain model, can be kept low by adding results from other experiments. The thermodynamic description of the melting process of statistical “pseudo-eutectical” copolymer systems yields structure parameters which can be used for the calculation of SAXS. The calculation itself is done using Hosemann's formula of the linear paracrystal, modified for our problem. The superstructure of the copolymer is assumed to be built up by clusters consisting of a certain number of stacked lamellae. A quantitative description of experimental SAXS can be established fitting alone the average number of crystal lamellae within the clusters of a simplified one-dimensional model of the super-structure. It is found that the number of lamellae within a cluster contributing to constructive interference modulation of SAXS is not only determined by the paracrystalline statistics but influenced too by the degree of dense packing of crystals according to the crystallinity of the copolymer systems.

ISSN:0022-2348    

DOI:10.1080/00222347408204549

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The values of the partition functions proposed in the Shindo model describing solvent-dependent protein denaturation have been evaluated using conformational potential energy functions. The denaturation curves of four proteins, lysozyme, ribonuclease-S, myoglobin, and α-chymotrypsin, were determined for different binary solvent mixtures composed of methanol, ethanol, water, formic acid, and acetic acid. The results suggest denaturation curves indicative of a cooperative process are possible only when the polar and nonpolar adsorbate concentrations differ by a constant. A comparison of some experimental transition free energies associated with polypeptides and those computed from the comformational potential energy functions indicates the calculations presented in this paper are realistic.

ISSN:0022-2348    

DOI:10.1080/00222347408204550

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A simplified method of intramolecular energy calculations was derived to set up helical molecular models for X-ray analysis. The calculation is made only for the possible conformations permitted by the fiber identity period, and the numbers of monomeric units and of turns in the fiber period. By utilizing the initial X-ray data, the number of variables for energy calculations is reduced. This method was applied to poly(ethylene oxide) and isotactic poly(propylene oxide) in order to confirm the validity, and the calculated stable conformations gave good coincidence with the results of X-ray analyses.

ISSN:0022-2348    

DOI:10.1080/00222347408204551

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Asperities have been found on the surfaces of commercial poly(ethylene terephthalate) films. These are the protruding sections of gel particles embedded in the bulk polymer. Because they are weaker than the surrounding bulk polymer, they may be collapsed, between grounded pressure electrodes, into C-and S-shaped pits. A statistical analysis of the number of pits formed per unit area, as functions of pressure, pressure application time, and sample preparation, has indicated that structural changes occur in both bulk polymer and asperities, and that these establish the asperity-pit relationship.

ISSN:0022-2348    

DOI:10.1080/00222347408204552

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A polymer of methyl methacrylate with a fractional content of isotactic triads exceeding 0.99, a viscosity-average molecular weight of about (5—6) 105and a normal glass temperature of 47°C, is investigated at pressures up 2 kbar and in a temperature range of 9 to 190°C. The results are compared with those for corresponding conventional polymers with glass temperatures above 100°C. In the liquid state, the thermal expansivity a of iso-PMMA, the internal pressure and the reduction in internal energy upon compression are larger, whereas the compressibility K is slightly smaller at elevated temperatures. In the glassy state, both α and K are smaller. The results are in qualitative accord with the existence of a weaker molar cohesion and/or greater chain flexibility, and closer packing in the stereoregular polymer. The application of the hole theory to the liquid shows the good agreement observed for other polymers in respect to the thermal expansivity, compressibility factor, and energy change with pressure. The differences in the scaling factors of the two polymer species are discussed in terms of cohesive and packing effects. Finally we consider the respective hole fractions at Tg and their temperature dependence in the glassy state.

ISSN:0022-2348    

DOI:10.1080/00222347408204553

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Dependence of the glass-transition temperature, Tg, on polymer chain flexibility predicted by the Gibbs-DiMarzio theory was empirically tested by studying the relationship between Tgand the stiffness parameter for isolated chains, [sgrave]. It was found that [sgrave] is not a single variable controlling Tgfor different polymer series which have different free volume fractions at Tg as a result of intrinsic differences in packing density in the crystalline state. The results obtained suggest that Tgof linear polyethylene lies near 160°K. A functional form of dependence of Tgon chain stiffness parameter and on local chain packing coefficient at Tgis proposed.

ISSN:0022-2348    

DOI:10.1080/00222347408204554

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor