摘要:

The states of aggregation of poly(γ-methyl glutamate) molecular chains in α-helical form were investigated. In a film cast from a gelatinized solution in pyridine (group 2 solvent), network structures of fibrils were observed and a (1010) plane of the crystallites showed a uniplanar orientation to the film surface. When the film was cast from a cholesteric liquid crystalline solution in dichloroethane (group 1 solvent), crystallites or microfibrils were dispersed separately and a planar orientation of molecular axes was induced. The dynamic mechanical properties of poly(γ-methyl glutamate) in α-helical form were studied for these specimens showing the different states of aggregation. A large tan δ peak was found in the dynamic viscoelastic measurements at around 420 K for the film cast from pyridine solution. From X-ray diffractometry and infrared spectroscopy it was confirmed that this is a crystalline relaxation and is associated with two relaxation mechanisms. The α1relaxation process, located at around 420 K, was attributed to the process of shear deformation of α-helices in the crystalline regions accompanying the mutual slip of the α-helical chains, and the α2relaxation process located at around 450 K was attributed to tensile deformation of α-helices permitting an accordionlike vibration of the α-helical chains along their axes. The magnitude of the crystalline relaxation was remarkable only for the film cast from pyridine solution, a feature attributed to the network structure formed by the microfibrillar connections revealed by electron microscopy.

ISSN:0022-2348    

DOI:10.1080/00222348208205083

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Morphological changes occurring in amorphous poly(methyl methacrylate) and polystyrene due to deformation near the glass transition temperatures were studied by transmission electron microscopy. Supermolecular heterogeneities were revealed by using the method of surface decoration of samples with gold prior to deformation. Deformation is accompanied by the formation of a band structure of slightly deformed material which is roughly perpendicular to the direction of deformation. The band width (nonhomogeneity of deformation) increases with temperature and is independent of the magnitude of deformation. In little-deformed domains more rigid particles emerge on the surface, indicating the supermolecular heterogeneity of polymers. The suggested model of microdeformation of amorphous polymers explaining the formation of the surface band structure is consistent with the bulk morphology revealed by high-frequency plasma etching.

ISSN:0022-2348    

DOI:10.1080/00222348208205084

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The crystallization ofBombyx mori L.silk fibroin was carried out from a regenerated solution maintained in contact with air under a steady-state flow. The nucleation occurs at first close to the solution surface after a few seconds of stirring and then a fibrillar crystal propagates. The nucleation was considered to occur by the flow-induced, one-dimensional orientation of silk fibroin molecules which were adsorbed to the solution surface. The yield of precipitate after stirring for 2 hr was influenced by the temperature and concentration at low shear rate (below 200 sec−1), while it was not influenced at high shear rate (1000 sec−1), and was above 80%. Electron microscopy, X-ray diffraction, and DSC thermograms show that the precipitates consist of fine fibers of about 0.2 μm diameter and crystals which have the β-structure and a low orientation.

ISSN:0022-2348    

DOI:10.1080/00222348208205085

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The effect of the solidification pressure and cooling rate on the initial isothermally measured enthalpy δhrof polystyrene has been determined. It was observed that δhrincreased slightly but nearly linearly with solidification pressure up to 4100 bar and it increased linearly with log (cooling rate) from 0.125 to about 8000°C/min. Further, the slope of the δhrvs. log (cooling rate) curves are independent of pressure. These data allow us to predict the enthalpy state of glassy polystyrene by control of the two parameters, cooling rate and pressure, in the absence of other perturbations.

ISSN:0022-2348    

DOI:10.1080/00222348208205086

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Krigbaum's modulus theory and its application to polyethylene which was irradiated with γ-rays are discussed in this article. The results indicate that an amorphous chain in a crystalline polymer varies from an inverse Langevin chain to a Gaussian chain with increasing temperature. Krigbaum's parameter Nn(t), the number of statistical segments present in an amorphous chain when its two ends have just deposited themselves on the surface of a growing crystallite, did not depend on the degree of degradation in a sample. By applying Krigbaum's modulus theory to a degraded sample, it was found that the ratio of the theoretical initial Young's modulus for a degraded sample to that for an undegraded sample, E0(t)/E0(0), increased with the degree of degradation in the sample. It seems to be caused by the greater increase of the degree of crystallinity in a degraded sample with such an increase being expected on the basis of the assumption that, after the amorphous regions in a sample degrade, some of the remaining unsevered amorphous chains can crystallize more readily.

ISSN:0022-2348    

DOI:10.1080/00222348208205087

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

It is shown that semiflexible polymers exhibit lyotropic liquid crystallinity once a threshhold solution concentration is surpassed. These polymers, namely polyisocyanides, polyorganophosphazenes, polyacenaphthylene, and cellulose derivatives, are characterized by persistence lengths or characteristic ratios experimentally determined to be intermediate between the very large ones belonging to extended rod polymers and the small ones belonging to flexible coil polymers. At the same time, the coefficient a in the Mark-Houwink equation of these polymers is of a magnitude typical of coiled molecules. Thus the semiflexible polymers adopt the configuration of expanded coils. The ability to pass through an anisotropic state in solution (and in the bulk below the melting point) is shown to be dependent on the ratio of the persistence length to the polymeric chain diameter, a relationship dependent on the flexibility of the chain and originating from Flory's theory of semiflexible chain molecules. Except for cellulose acetate all the studied polymers showed in the bulk only a lateral interchain ordering and no conventional crystallinity. This one-dimensional order was retained in the liquid crystalline solutions.

ISSN:0022-2348    

DOI:10.1080/00222348208205088

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Structural determinations, obtained through density, birefringence, and WAXS measurements, are reported for nylon 6/inorganic salt fiber samples as a function of draw ratio. They confirm the possibility of achieving very high amorphous orientation in these systems. Dynamic-mechanical data have also been collected which allow determination of glass transition temperatures. These are also discussed in terms of structural parameters.

ISSN:0022-2348    

DOI:10.1080/00222348208205089

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The measurements of piezoelectric constant e = e' - ie“, elastic constant c = c' + ic”, and dielectric constant ϵ = ϵ' - iϵ” at 10 Hz for poly(hydroxy ethyl glutamine) showed relaxations at -40 and -100°C, suggesting the thermal motion of side chains. The variation of these constants with hydration was interpreted by a model of parallel piezoelectric rods dispersed in the non-piezoelectric medium. If the α-helical main chains with bound water of 0.36 g/g were assumed to form piezoelectric rods, the calculated values agreed well with the observed values for more hydrated samples.

ISSN:0022-2348    

DOI:10.1080/00222348208205090

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor