摘要:

Thermooptical, wide-angle x-ray diffraction and morphological investigations of blends of isotactic polypropylene with linear polyethylene revealed an increased crystallization rate of the polyethylene blend component, compared to crystallization of polyethylene alone. Crystallization behavior of the polyethylene component was markedly dependent on the blend thermal history and on the circumstances of the polyethylene phase—whether it was disperse or continuous. The higher crystallization rate of the polyethylene component was related to the presence of various types of heterogeneous crystallization nuclei in the blend and to the stabilizing action of the solid polypropylene matrix on minute polyethylene crystallites which survived above melting temperature.

ISSN:0022-2348    

DOI:10.1080/00222348808245759

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The reversibility of solvent swelling and the existence of an equilibrium swelling ratio, qeq, has been established for pigment gallstone particles. A simple technique was devised to demonstrate that solvent imbibition in pigment gallstone particles is reversible. This finding confirms unequivocally that the molecular makeup of pigment gallstones involves polymer networks. In addition, this new method permits serial direct observation of the interactions between pigment gallstone particles and the solvent. Application of the technique to other network polymers should be readily possible.

ISSN:0022-2348    

DOI:10.1080/00222348808245760

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Scaling in terms of temperature, composition, and molecular weight variables has practical and fundamental significance. The viscosity of polymer solutions deviates from that predicted by the Huggins equation when the concentration is higher than a characteristic concentration cch. The value of cchdepends on the molecular weight of the polymer and the thermodynamic conditions of the system. It is also a known fact that the deviations are due to the entanglements and interactions of polymer molecules. Therefore, we believe cch can be used as a concentration-reducing parameter to get the superposition curves. It can be shown that the concentration corresponding to a minimum value of ηsp/ch2(in the case of ηsp/c2vs concentration curves) is the value of cchof that system. Moreover, this cchis related to the intrinsic viscosity and molecular weight through the Huggins and Mark-Hauwink-Sakurada equations (cch= k′M−a′). Using cchvalues for different systems and plotting log ηrversus C/Cch, the superposition curves are obtained. In each case these curves are found to be linear, at least when concentrations approach zero. Master curves may be plotted by making use of the initial slopes of the curve (log ηrvs Bc/cch) and it is found that the data obtained at different thermodynamic conditions fit these (log ηrvs Bc/cch, B being the initial slope of log η vs c/cch) curves very well. The slopes are also compared to k′, a′, and the expansion coefficient of the system and the relationships are found to be linear. It is concluded that cchis a better parameter for the superposition of viscosity data, as well as being easy to obtain experimentally.

ISSN:0022-2348    

DOI:10.1080/00222348808245761

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Polystyrene latexes with 40-60 nm diameter and molecular weights ranging from 6 × 104to 6 × 106g/mol were synthesized by a two-step equilibrium swelling method, with deuterated polymer forming either the first or second step. Below about 1 × 106g/mol, small-angle neutron scattering gave zero-angle scattering intensities much higher than expected on the basis of gel permeation chromatography molecular weights. Several models were examined, the leading model based on a core-shell latex structure. The development of such structure was found to depend on the ratio of the radius of gyration of the polymer chain to that of the diameter of the latex particle, reaching a maximum in the range where the polymer chain dimensions are about half that of the latex particle. For the highest molecular weights, normal scattering intensities were found. These results lead to the finding that the polymer chains were compressed in the latex particles with constraining in the range of one to four, for this molecular weight range.

ISSN:0022-2348    

DOI:10.1080/00222348808245762

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Bulk polystyrene film samples were made from a 50% deuterated latex with a molecular weight of 5.85 × 106g/mol and 38 nm particle diameter. Because of the high molecular weight and small particle size, these chains are constrained in dimensions by a factor of four. Mildly molded (compacted to full density) samples were annealed for increasing time periods and their small-angle neutron scattering (SANS) patterns recorded. The radii of gyration increase with time as segmental diffusion proceeds during film formation. The initial diffusion was hindered, as shown by a slower than expected relaxation of the chains. Residual interfacial effects were postulated to be the main cause. Chain interdiffusion between latexes of about 110 Å is sufficient to develop a tough, coherent film.

ISSN:0022-2348    

DOI:10.1080/00222348808245763

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In earlier publications it has been reported that plasmapolymerized organosilicon films may contain up to 6.8 wt% water. A distinction has been made between “weakly” and “strongly” bound water in the polymer matrix, the strongly bound water being incorporated into the film in the form of network aggregates connected with the glass by means of hydrogen bonds. The observation in those materials of a phase transition is due to the changed inner structure of the aggregates in question. The goal of this study is the determination of the effect of absorbed water on the dielectric properties of plasma-polymerized organosilicon films. It is shown that the weakly bound water activates a relaxation process whose frequency at room temperature is above 0.5 MHz. In contrast, the strongly bound water reveals its presence by two relaxation processes of very low frequency, with activation energies of 0.65 eV and 0.87 eV. It was found that the absorbed molecules of strongly bound water may also inhibit the rotation of certain matrix dipoles.

ISSN:0022-2348    

DOI:10.1080/00222348808245764

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The structure-property relationships of polyurethane elastomers based on 4,4′-diphenylmethane diisocyanate (MDI) and 4,4′-dicyclohexylmethane diisocyanate (HMDI) with PTMO, PDMS, and mixed PTMO/PDMS soft segments were investigated using DSC, dynamic mechanical spectroscopy, tensile testing, and SAXS. Changes in water absorption and moisture sensitivity with compositional changes were investigated through water absorption and physical property measurements. Differences in tensile properties and moisture sensitivity with varying hard and soft segment composition are interpreted in terms of the phase mixing characteristics of the various polymers studied.

ISSN:0022-2348    

DOI:10.1080/00222348808245765

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

An isolated, flexible polymer chain in dilute solution assumes a random configuration. In reality such a polymer coil is not completely random, because an excluded volume effect requires a modification from randomness. In addition, the coil placed in a better solvent is more expanded than that in a poor solvent. In other words, the polymer chain segments in a better solvent are more extended, compared to those in a neutral solvent. In the present study we have discovered an indication that the chain segments lying on the periphery of the coil are more extended than those in the interior. This discovery has been made in the course of relating intrinsic viscosity to thermodynamic interaction between polymer and solvent. The resulting relationship provides a means of evaluating the thermodynamic interaction parameter from the measured value of intrinsic viscosity, if the molecular weight of the polymer, its intrinsic viscosity in a neutral solvent, and the degree of excess extension of chain segments are known. The last is the parameter discovered in this work. This observation is independent of particular thermodynamic theory, so long as the experimental data are used in a consistent manner. In this work Maron's theory was used, because it is applicable to infinite dilution as well as concentrated solutions.

ISSN:0022-2348    

DOI:10.1080/00222348808245766

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The electrical conductivity of polyphenylene sulfide doped with ferric chloride using various solvents has been studied as a function of dopant concentration, temperature, etc. The conductivity (a) was found to increase by almost 10 orders of magnitude by using certain doping media and the the concentration (σ) dependence followed a power law of the type σ α cnwhere n has a value between 5.5 and 6.0. The temperature dependence of conductivity revealed two distinct regions with the activation energy having low (0.3-0.5 eV) and high (1.5-2.5 eV) values, respectively. The x-ray diffraction studies show no major changes in the crystalline structure/crystallinity even at high doping levels. These various findings have been explained on the basis of preferential diffusion of the dopant in the amorphous regions and the formation of a two-phase system.

ISSN:0022-2348    

DOI:10.1080/00222348808245767

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor