摘要:

Zero-shear viscosities of solutions of poly [2-methoxy-4,6-di(p, p′-isopropylidene diphenyloxy)-s-triazine] in chloroform were measured at various temperatures. The viscosity data were analyzed in terms of Martin's and Fedor's relationships. The temperature dependence of viscosities indicates that the apparent activation energy for viscous flow increases and the preexponential factor, related to activation entropy, decreases with concentration of polymer solution. The parameter Cm, related to volume fraction of polymerm, was found to be linearly dependent on temperature. The viscosity-concentration data were generalized in terms of reduced variables.

ISSN:0022-2348    

DOI:10.1080/00222348408219465

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The glass transitions in talc- and titanium-dioxide-filled free films of hydroxypropyl methylcellulose (HPMC) as well as HPMC in combination with either polyethylene glycol (PEG) 400 or polyvinyl alcohol (PVA) have been examined by differential scanning calorimetry. The glass transition temperatures (Tg's) of HPMC and HPMC/PEG 400 films were increased in the presence of either talc or titanium dioxide, with the former the more effective Tgenhancer. In contrast, the Tg's of HPMC/PVA films were virtually unchanged in the presence of the fillers, and this behavior was attributed to the influence of the vinyl backbone of PVA. The Tg's of filled and unfilled HPMC and HPMC/PVA films were lower after storage for 1 year, but the Tgof HPMC/PEG 400 remained unchanged. Phase separation of the mixed polymer systems also occurred following prolonged storage. These phenomena were related to changes in the moisture content and crystal-linity of the films.

ISSN:0022-2348    

DOI:10.1080/00222348408219466

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Polycyanurates were prepared by interfacial polycondensation of 2-methoxy-4,6-dichloro-s-triazine (MDT) jointly with bisphenol-A and bisphenol-C using a chloroform-water system and different molar proportions of the reactants. The copolymer compositions of the tercopolymer samples were estimated by analysis of NMR spectral data. One tercopolymer sample was fractionated by fractional precipitation. The fractions were characterized by measurements based on viscometry osmometry and gel permeation chromatography. The intrinsic viscosity data were analyzed in terms of the Mark-Houwink-Kuhn-Sakurada (MHKS) relation. The unperturbed dimensions and polymer-solvent interaction parameters were estimated by the application of the current theories of excluded volume effect.

ISSN:0022-2348    

DOI:10.1080/00222348408219467

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Measurements of small-angle x-ray diffraction (SAXD) were performed for nylon 6 samples quenched from the melt at various crystallization temperatures T (°K). The spacing estimated from the position of maximum intensity in a SAXD diagram, which is assumed to be equal to the thickness of lamellar crystals ℓ, decreases with the decrease of T. The behavior was analyzed in terms of nucleation theory. In applying the theory. the contribution of γ-form crystals for the samples crystallized at lower T was considered. For this purpose wide-angle x-ray diffraction and infrared data obtained for the same samples used in SAXD measurements were used. It was shown that the relation of ℓ versus T deviates remarkably from the theoretical prediction under the premise that the surface free energy σe(ergs/square centimeter) is constant with T. We present an approach to the analysis of the data from the standpoint that σeis a parameter changing with T, where σeshould be interpreted as related to the degree of irregularity of the fold surface of lamellar crystals. The values of σethus obtained increase with increasing undercooling δT, where δT = Tm− T, with Tm(°K) being the melting point. SAXD data of polyethylene reported earlier by Mandelkern et al. were analyzed from the same standpoint, and it was found that the values of σeincrease with δT/Tmin a similar manner for both nylon 6 and polyethylene.

ISSN:0022-2348    

DOI:10.1080/00222348408219468

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Temperature effects on fatigue crack propagation in glassy polymers can be described by the Chudnovsky and Moet model, which is based on the propagation of microdefects near the crack tip. This was shown by fitting several models to fatigue data for polycarbonate and poly (methyl methacrylate). Statistical regression analysis and a global search method were used in the model fitting.

ISSN:0022-2348    

DOI:10.1080/00222348408219469

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The dynamic torsional characteristics of a difunctional, bisphenol-A-type epoxy resin cured with different amounts of metaphenylene diamine, using two cure cycles, were determined in torsion at four frequencies between −150° and 200°C. Besides two prominent relaxations, α and β, a third broad, but not very intense, relaxation has been shown to be present in all samples in the intermediate temperature range and has been designated the α transition. An analysis of the data on the temperature and frequency dependence of these relaxations allows some insight into their possible molecular origins. The torsional moduli were found to be related to the molecular packing, as reflected in their densities.

ISSN:0022-2348    

DOI:10.1080/00222348408219470

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The relation between the temperature Tαof the dipolar relaxation, obtained by the technique of thermally stimulated currents (TSC) and the glass transition temperature Tghas been studied in amorphous poly(ethylene terephthalate) samples. The temperature Tαdepends fundamentally on the polarization temperature Tp, the polarization time tp, and the heating rate v. For each heating rate a maximum Tα, TM, was obtained for an optimum polarization temperature Tpo. The value of Tpois 70°C, independent of the heating rate, and very close to the glass transition temperature obtained by differential scanning calorimetry (69°C). The resulting value for TMcoincides with Tpoin the limits of null heating rate and null isothermal polarization time, and, consequently, TMgives the value of the glass transition temperature for each heating rate as a function of the isothermal dipolar contribution on polarizing at the temperature Tpo.

ISSN:0022-2348    

DOI:10.1080/00222348408219471

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A strain-induced crystallization behavior of hydroxypropyl cellulose (HPC) from the thermotropic liquid-crystalline state is described based on morphological observations by electron microscopy. It is shown that originally round-shaped particles behave as a structure unit in formation of a variety of supermolecular architectures of HPC films prepared from the thermotropic melt under shear. In an oriented HPC film obtained under weak shear, many round particles are elongated and aligned in the direction of shear (SD), but with their bodies bent to some degree. As deformation increases further, fibrillation occurs on the surface of the elongated particles, and then the resulting fibrils are arranged in a zigzag fashion along the SD to form a banded structure. In some cases, a pleated arrangement of fibrils is noticeable between bands. The structural transformation mechanism of thermotropic HPC under shear is discussed in detail on the basis of the morphological evidence.

ISSN:0022-2348    

DOI:10.1080/00222348408219472

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Using two types of thermotropic liquid-crystal polymers, experimental results reconfirmed previous reports that the relaxation time of extruded liquid-crystal polymers is much longer than that of conventional polymers. The initial modulus and elongation of sheets extruded with liquidcrystal polymers were found to be strongly dependent on the gauge length. In addition, it was observed, for the first time, that the mechanical properties of the extruded thermotropic copolyesters follow the general equations for fiber-reinforced composites such that the angular dependence of the tensile strength of the extruded liquid-crystal polymeric sheets obeys the Tsai-Hill theory, while the angular dependence of the initial modulus follows the Lees equation. These results suggest that the highly oriented liquid-crystal domains may be considered as reinforcing fibers in the extruded articles, and their mechanical properties can be predicted using existing composite theories.

ISSN:0022-2348    

DOI:10.1080/00222348408219473

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

It is shown that in blends of PE having different melting temperatures the morphology depends drastically on the cooling rate. In these heterogeneous PE, the correlation relationship L = r between the long period L of the solid state and the dimension of the coils r in the liquid state is observed only in rapidly quenched materials. In slowcooled materials the SAXS spectra are interpreted in terms of segregation of two types of PE, on a scale of the order of the dimension of the coils, the arrangement of the crystalline lamellae being paracrystalline and statistical.

ISSN:0022-2348    

DOI:10.1080/00222348408219474

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor