摘要:

Reconsidered and discussed in the present work is the limited possibility of the application of the orientation parameter for characterization of the orientation behavior of segments of polymer chains during deformation when this parameter is calculated from IR dichroism with inversion of dichroism for several absorption bands. Studies on orientation effects in uniaxial deformation of a polyether-urethane-urea elastomer obtained on the basis of polytetra-methylene glycol with a molecular mass of about 1000, 2,4-tolylendiisocyanate, and 4,4′- diphenylmethanediamine have been made using the x-ray diffraction technique. The results of the investigations agree with the assumption that in the polymer investigated conformation transitions in hard segments may be responsible for the IR dichroism inversion.

ISSN:0022-2348    

DOI:10.1080/00222348308224772

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Solution-cast films of a polyurethane based on 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) as the hard segment and poly(propylene oxide) endcapped with poly(ethylene oxide) (PPO-EO) as the soft segment were examined by optical and electron microscopy, electron diffraction, and wide-angle x-ray scattering. Hard segment content was 77 % by weight. The soft segment is atactic so all crystallinity is isolated to the hard segment phase. Two crystal forms of the hard segment have been observed, with their associated spherulites. Type I crystals are intrinsically disordered and exhibit only a few diffuse diffraction rings. Type I crystals also form nonbirefringent spherulites. Type II crystals form negative spherulites. Darkfield electron microscopy indicates that type II crystals are lath shaped and average about 12 nm in width by about 50-70 nm in length. Type I crystals were not able to be resolved by dark-field or bright-field transmission electron microscopy, indicating that the crystals are very small, less than 10 nm.

ISSN:0022-2348    

DOI:10.1080/00222348308224773

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Dielectric and viscoelastic properties of solid amylose were investigated by thermally stimulated current and creep techniques in order to clarify the relation between its structure and properties, and also the different binding modes of water molecules. Several current peaks were observed, and these were decomposed into elementary processes by the fractional polarization technique. A peak at about —110[ddot]C was attributed to the rotational motion around the C5-C6 axis of methylol groups attached to the C5 atom in the glucose residue. A peak at about — 50dGC was attributed to bound water: This peak was eliminated by drying the specimen. A peak at about —230[ddot]C was attributed to another kind of bound water. A peak at about 30[ddot]C was attributed to dehydration during the experiment. Thus, three different relaxation modes of bound water were separated by the present work.

ISSN:0022-2348    

DOI:10.1080/00222348308224774

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The crystallization of isotactic polybutene-1 (PB-1) from dilute solutions was studied by Holland and Miller, who observed that the resulting crystal structure was dependent on the temperature of dissolution as well as the temperature of crystallization. Their study has been reexamined and further explored in detail under more general experimental conditions. The effect of using different crystal polymorphs as the starting material and that of keeping the solution for various lengths of time at selected temperatures before crystallization have been studied. The results generally agree with the previous findings of Holland and Miller and provide further information which suggests that PB-1 molecules assume definite helical conformations in solution. With time, the chains tend to transform from their original solid-state conformations to the one which is thermodynamically favored at the solution temperature.

ISSN:0022-2348    

DOI:10.1080/00222348308224775

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A series of polyester-based polyurethanes were prepared using polycaprolactone diols and triols of different molecular weights and 4,4′-diphenylmethane diisocyanate and 1,4butanediol. Samples of differing percent of hard segment (0, 23, and 43 %) and different molecular weight of macroglycol were made. Crosslinked polyurethanes obtained from macrotriols (Mn= 540 and 900) were compared with linear polyurethanes obtained from macrodiols (M =530 and 830) in order to understand the effect of chemical cross-links in addition to the physical interactions on the phase separation phenomenon. These materials exhibit a range of mechanical behavior from soft elastomers to tough semicrystalline materials. The 0 % hard segment samples are single-phased amorphous materials. All the 23 % and 43 % hard segment content materials are semicrystalline and display phase separation on the scale of microns and below. In macrodiol samples hard-segment-rich spherulites are present, while in macrotriol samples only hard-segmentrich globules are observed. Indications of two-phase behavior in the 23 % and 43 % hard-segment content materials were also deduced from thermal analysis and dynamic mechanical behavior.

ISSN:0022-2348    

DOI:10.1080/00222348308224776

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

It is shown that polyethylene and polyethylene terephthalate fractions, quenched from the melt, crystallize in a similar manner; the long periods in these materials obey the general lawwhere lcis the crystalline lamella core thickness independent of the molecular weight M, and α is a parameter dependent on the rigidity of the chain in the liquid state before crystallization. In annealed linear and branched PET materials, the similar dependence of the long periods on the supercooling above the temperature T* = 200°C is explained by the dynamic flexibility of the chains in the solid state; according to the rule of O'Leary and Geil, this temperature corresponds to the temperature Tαof mechanical relaxation.

ISSN:0022-2348    

DOI:10.1080/00222348308224777

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The elastic modulus E1of crystalline regions of poly(β-trichloromethyl- propiolactone) (PTCPL) in the direction parallel to the chain axis has been measured by the x-ray diffraction method. PTCPL was obtained by solid-state polymerization. The value of E1for the (014) plane of PTCPL was 25 × 104kg/cm2, whereas the value of the specimen modulus (Y1) was 10.3 × 10.3 × 104kg/cm2. The value of Y1is very low compared with that of E1from the viewpoint of microstructure. These results are discussed in terms of the molecular conformation in the crystalline regions and the crystal defects.

ISSN:0022-2348    

DOI:10.1080/00222348308224778

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The yield stress of nylon 6 (Ny6) composites filled with ultrafine and micron-sized (SiO2and glass) particles was measured as a function of temperature, rate of strain, and filler content. The yield stress of the composites filled with ultrafine SiO2particles increased with filler content and decreased with filler size, whereas for composites filled with glass particles, this relation was reversed. For ultrafine SiO2filled composites, the tensile yield stress was found to be reducible with regard to temperature, rate of strain, and filler content. At a given filler content, composite curves were obtained for yield stress plotted against the logarithm of the strain rate. The Arrhenius plot of the shift factors for composing the strain rate-temperature master curve formed a single curve irrespective of the filler content and size. The curve comprised two linear regions with a break appearing at 110[ddot], corresponding to a transition of the matrix polymer. The master curves obtained for different contents of a given size filler could be further reduced into a grand composite curve by shifting them along the axis of strain rate, with logarithmic second shifting them along the axis of strain rate, with logarithmic second shift factors proportional to the volume fraction of the filler. The dependence of the yield stress on the filler volume fraction and size is explained by a modified equation based on the dispersion strength theory with an aggregation parameter incorporated.

ISSN:0022-2348    

DOI:10.1080/00222348308224779

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor