摘要:

The decay of polymer radicals in γ-irradiated polyethylene as measured by EPR is discussed from the viewpoint of a continuous but not constant distribution over the activation free energy and of the kinetic constants. The possibility of determining this distribution from experimental results alone is shown. In addition, the new treatment enables us to obtain more clearly the various temperature regions in which radical decay takes place most rapidly, and this allows a distinction by EPR, for instance, even between several kinds of low-density polyethylene.

ISSN:0022-2348    

DOI:10.1080/00222348308215498

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Differential scanning calorimetry has been found useful in studying the kinetics of the Tg. The method commonly used involves annealing the polymer at temperatures below Tgfor various periods of time and then measuring the enthalpy change in going from the glassy to the liquid state as a function of annealing time and temperature. However, annealing below Tgis a slow process, and therefore the quantity of research that can be done by this method is limited. Moreover, the above method measures primarily the kinetics of the annealing process. We are also interested in the kinetics of the transition from the glass to the liquid state.

ISSN:0022-2348    

DOI:10.1080/00222348308215499

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Chain lengths have been calculated from the peak positions of the longitudinal acoustic modes (LAM) of polyethylene single crystals grown at several different temperatures. The data are consistent with other experimental results when the crystalline elastic modulus is taken to be 3.6 × 1012dyn/cm2. However, this is true only if the vibrations of the crystalline chain segments are unaffected by the presence of folds and cilia on the crystal surface. The LAMs of several crystal preparations were also deconvoluted with the first-order LAM of C94H190in order to remove instrumental broadening. The band shapes of the deconvoluted spectra are consistent with the idea that the LAM of polyethylene crystals is composed of two contributions: One due to chain stems in 110 sectors and a second due to chains in 200 sectors.

ISSN:0022-2348    

DOI:10.1080/00222348308215500

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Shear stress growth and relaxation behavior of two well-characterized SBS block copolymers have been studied using a Melt Elasticity Tester. Effects of casting solvents on the transient rheological properties and structure variation during flow are determined via samples cast from THF/MEK and cyclohexane. The temperature dependence of the observed shear stress at the yield point and steady-state viscosities provides insight into the mechanism of structure breakdown induced by the applied flow. Shear stress relaxation upon cessation of flow reveals complex behavior, depending on temperature, casting solvents, and duration of previous flow. Strain recovery data have also been obtained, indicating strong dependence on the composition of the copolymers. Significance of these observations in terms of the melt structure of SBS is discussed.

ISSN:0022-2348    

DOI:10.1080/00222348308215501

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Phase relationships in concentrated solution and in the bulk of a solvent/rigid-rod/flexible-coil system were investigated. The solvent was a mixture of two strong acids. The rigid-rod polymer was poly-p-phenylenebenzobisthiazole (PBT). The flexible-coil polymer was poly-2,5(6)benzimidazole (ABPBI). The concentrated solution and bulk morphologies were investigated by means of polarized optical microscopy, small-angle light scattering, scanning electron microscopy, and wide-angle x-ray diffraction techniques. Above a critical concentration, Ccr, the pseudo ternary solution separated into two coexisting phases, one optically anisotropic (liquid crystalline) and the other isotropic. The anisotropic domains were highly birefringent. They contained primarily the PBT macromolecules oriented perferentially along a domain axis. Numerical values of Ccr, determined experimentally, were in good agreement with calculated predictions. Aggregates composed of PBT molecules were observed to be dispersed in a continuous matrix for vacuum-cast films. These results strongly indicate the dominance of entropic effects in the thermodynamics of rigid-rod/flexible-coil polymer mixtures. The feasibility of processing these novel mixtures into “molecular level composites” (molecular composite) having rigid-rod molecules or small bundles of these rod molecules dispersed in a continuous flexible-coil matrix is demonstrated. These composites possess excellent tensile properties and may be “tuned” to virtually any desired combination of their composite properties; for example, uniaxial modulus, ultimate tensile strength, and elongation.

ISSN:0022-2348    

DOI:10.1080/00222348308215502

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

ISSN:0022-2348    

DOI:10.1080/00222348308215503

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Three types of aromatic polyamide fibers (Kevlar, Kevlar-49, and PRD-49) were studied by transmission electron microscopy, secondary electron imaging, and electron diffraction techniques. Ultramicrotomy, ion-thinning, and brittle fracture techniques were used to prepare specimens which revealed both longitudinal and transverse fiber structures. Aromatic polyamide fibers exhibit both a “skin” and a “core” structure. The core morphology is shown to be consistent with a layered structure where individual layers are stacked perpendicular to the fiber axis and are composed of rodlike crystallites whose c axes are parallel to the fiber axis. Electron diffraction results indicate that hydrogen bonds are located nearly in the radial direction of the fiber. The crystallite layer thickness appears to depend upon the most probable molecular weight of the fiber. Longer crystallites which pass through two or more layers are present, and may control the strength of the fiber in the axial direction.

ISSN:0022-2348    

DOI:10.1080/00222348308215504

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The molecular structures of the hydrolyzates of γ-aminopropyl-triethoxysilane (γ-APS) were studied by Fourier transform infrared spectroscopy (FT-IR). The molecular structure of γ-APS is a function of the pH of the solution and the drying conditions. In the partially cured film, cast from a 20% by weight γ-APS aqueous solution at pH = 2, the amine group exists as a protonated amine; and at pH = 12 the amine group exists as a free NH2. The amine group exhibits different structures subject to drying conditions when prepared at natural pH. The sample dried in nitrogen exhibited hydrogen bonding between the SiOH and the NH2group. Upon heating, the silanol groups condense and the amine groups no longer hydrogen bond. The increase in the availability of free amine groups was indicated by larger amounts of exchange of NH2to ND2when the sample was exposed to D2O vapor. When the hydrolyzecl γ-APS at natural pH was dried in CO2or in air, a bicarbonate structure was formed, causing the appearance of bands at 1630, 1575, 1488, and 1332 cm−1. These bands were previously associated with the intramolecular zwitterions of Sio−…NH3+E-glass fibers were treated with 2% γ-APS and dried under different conditions, which show the various structures of γ-APS as described above. Differences in γ-APS structures may affect the curing reactions of composite materials.

ISSN:0022-2348    

DOI:10.1080/00222348308215505

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The equilibrium state of polyethylene melt was studied by examining the effects of Tmeltand tmelton the long period of B melt melt quenched polyethylene. The long period was found to be proportional to M−½and to depend on Tmeltwith a temperature coefficient α = −0.5 × 10−3. When the melt temperature was changed from one to the other, a relaxation time (3 to 5.5 min) was determined based on long-period measurements. In addition, the relaxation time was found to be proportional to for polydisperse linear polyethylenes. These findings, long relaxation time and the M−3.3dependency, are discussed in light of current crystallization mechanisms and origins of the M−3.3dependency.

ISSN:0022-2348    

DOI:10.1080/00222348308215506

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Two series of polyether-polyurethane anionomers based on 4, 4′-diphenylmethane diisocyanate (MDI), methyl diethanolamine (MDEA), and polytetramethylene oxide glycol (PTMO) were synthesized. The system based on 1000-MW PTMO, which exhibits an interconnected hard domain morphology, showed a substantial decrease in the soft segment Tgupon ionization.

ISSN:0022-2348    

DOI:10.1080/00222348308215507

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor