摘要:

A high-performance aromatic polyimide fiber has been spun from a high molecular weight polyimide synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-dimethyl-4,4′-diaminobiphenyl (DMB). The fiber exhibits not only excellent tensile properties and high temperature resistance but also a high compressive strength of 655 MPa. Morphological observations of BPDA-DMB fibers indicate that the fiber shows a skin-core structure and microfibrillar textures. A banded texture can also be found with a spacing of about 2μm, which may be introduced by the liquid crystalline behavior that appears during processing. Compressed BPDADMB fibers form kink and microkink bands over different size scales. The detailed formation mechanism of these banded textures is discussed. The structure parameter changes during compression-including crystal unit cell parameters, apparent crystallinity, crystal and overall orientation, and apparent crystallite sizes-are monitored. It is found that after restretching, the crystal and overall orientation is almost fully recovered while the apparent crystallinity is not recoverable. The structural changes during compression are critically associated with the loss of macroscopic mechanical property in the fibers.

ISSN:0022-2348    

DOI:10.1080/00222349708212386

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The microhardness of films of poly(butylene terephthalate)-cyclo-aliphatic carbonate (PBT-PCC) block polymers was determined. The PBT-PCCcompositions investigated were 100/0, 95/5, 80/20, 70/30, 60/40, 50/50, and 40/60. The microhardness of the amorphous films is discussed in terms of a model given by the additivity values of the single componentsHaPBTandHaPc. Physical aging of the glassy samples leads to a rise in the microhardness for the various copolymer compositions. However, the hardness additivity of the aged samples is preserved. It is further shown that the deviation of hardness from the additivity law, for the semicrystalline copolymers, is mainly due to the depression of the crystal hardness values of the PBT crystals and partly due to a decrease in crystallinity of the PBT phase. Discussion of results makes it possible to derive a value for the microhardness of infinitely thick PBT crystals which is not far from that reported for poly(ethylene terephthalate).

ISSN:0022-2348    

DOI:10.1080/00222349708212387

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Nearly monodisperse spherical microgel particles of poly(N-isopropylacrylamide) (PNIPAM) were prepared by emulsion polymerization in water. The volume phase transition of the microgel particles was studied by static and dynamic laser light scattering (LLS) in terms of the radius of gyration (Rg) and hydrodynamic radius (Rh). The phase transition temperature of the microgel ∼33.0°C, similar to that of individual PNIPAM chains in water. The temperature independence ofRg/Rh(∼0.78 ± 0.03) shows that in both the swollen and collapsed states the microgels are uniform particles behaving as hydrodynamically equivalent spheres. About 94% of the water inside the microgel network is driven out during the phase transition. The volume change of the microgel particles is continuous, in contrast to the discontinuous volume change observed in some bulk PNIPAM gels. The microgel particles are thermodynamically stable even at their collapsing limit. The behavior of microgel particles is compared to that of individual PNIPAM chains.

ISSN:0022-2348    

DOI:10.1080/00222349708212388

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Epoxy network systems based on DGEBA (bisphenol-A-diglycidyl ether) with two kinds of polysiloxane with low molecular weight, ATPS (aminopropyldimethyl-terminated polysiloxane) and PTPS (phenyl-terminated polysiloxane), were prepared and annealed at 175°C. Their physical aging data were curve fitted with the Kohlrausch-William-Watts (KWW) equation and thermal expansion behaviors of both quenched and strained samples were investigated. Results show that curve-fitted ΔHereflects the relative amount of the “frozen-in” excess free volume in the epoxy network, related to the deviation from equilibrium state. With increase of the ATPS content, both Δl, which was defined as linear dimension drop per millimeter height of sample, and ΔHedecrease; that is, they change in the same direction.

ISSN:0022-2348    

DOI:10.1080/00222349708212389

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Aggregates of preoriented solution-grown crystals of nylon 6 were drawn by solid-state coextrusion both parallel and perpendicular to the initial lamellae. For the former, a solution-grown crystal mat, where the lamellae oriented parallel to the mat surface, was placed between split billet halves, and the assembly was coextruded. For the latter, a compacted crystal-powder billet, where the lamellae oriented perpendicular to the long axis, was inserted into a central hole of the predrilled billet, and the assembly was drawn by solid-state coextrusion. The deformation mechanisms for both initial lamellae orientations have been studied by wide-angle (WAXD) and small-angle x-ray scattering (SAXS). The effects of initial lamellae morphology and extrusion temperature were also studied. When the extrusion draw was made on a mat (parallel to the lamellar surface), a part of the initial lamellae were broken into smaller blocks and they rotated to make an angle to the draw axis. In these blocks, the molecular chains oriented along the draw axis. When the draw was made on a compacted billet (perpendicular to the lamellae), more complex changes in the morphology were observed at a small strain. Initially, the lamellae tended to orient with the fold surface parallel to the extrusion direction. At a higher strain, the transformation of lamellae to a fibrous structure proceeded in a manner similar to that observed for the drawing initially parallel to the lamellae surface. SAXS long period was markedly affected by extrusion draw temperature (Te). At a given extrusion draw ratio, the long period of a new fibrillar structure, calculated from the SAXS maximum on the meridian, was a unique function ofTeand increased withTe, independent of the predrawn morphology with different lamellar thickness.

ISSN:0022-2348    

DOI:10.1080/00222349708212390

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

It has been suggested previously that poly(phenylene sulfide) (PPS) contains a rigid amorphous fraction with different characteristics from those of the crystal phase and liquid-like amorphous phase, and that a three-component model is more suitable for some semicrystalline polymers including PPS. The rigid amorphous component has been assumed to be an interfacial region between the crystal phase and liquid-like amorphous phase, and the fraction depends greatly on the prior thermal treatment. This paper focuses on the interface to characterize the rigid amorphous component; the relationship between the rigid amorphous fraction determined by differential scanning calorimeter (DSC) and the one-dimensional interface fraction within two adjacent crystal lamellae determined by small-angle x-ray scattering (SAXS) is estimated. The two results showed a correlation: they revealed a similar tendency to decrease as annealing temperature and time increase. The chain mobility of PPS films could be detected by means of thermoluminescence (TL). From TL, we found that the interfaces and the crystal domains become more stable with higher degree of annealing, a result which corresponds to the results obtained from the DSC and SAXS experiments.

ISSN:0022-2348    

DOI:10.1080/00222349708212391

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Polystyrene microparticles prepared by microemulsion free-radical polymerization have been investigated using a scanning tunneling microscope. It has been found that the polymer chains are extended without entanglement in some regions of the polymer surface. The hydrogen atoms on the upward rim of the phenyl groups can be distinguished by atom-resolved imaging. The phenyl groups in the same chain can stack up as a parallel-displaced structure, similar to that predicted for benzene dimers. The existence of the orderly stacked polymer chains and phenyl groups may be due to the fact that the polymerization is constrained in a very limited space.

ISSN:0022-2348    

DOI:10.1080/00222349708212392

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Diffusivity, permeability, and sorptivity of benzene and substituted benzenes through crosslinked epoxidized natural rubber (ENR) at 27°, 40°, and 60°C have been determined. Four different vulcanizates of ENR were used for the experiment: viz., efficient (EV), conventional (CV), dicumyl peroxide (DCP), and a mixture consisting of sulfur and peroxide (mixed). The effect of different vulcanizing system and size of solvents on transport has been studied. Thermodynamic quantities such as enthalpy and entropy change of the sorption process were calculated from equilibrium sorption data. Arrhenius parameters for the process of diffusion and permeation were also estimated. The polymer-solvent interaction parameter was also determined. The experimental results were compared with theoretical predictions.

ISSN:0022-2348    

DOI:10.1080/00222349708212393

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In recent years, water-soluble polymers, or hydrogels, with a lower critical solution temperature (LCST) have been intensively studied. One typical example is poly(N4sopropylacrylamide) (PNIPAM) and its gel. The influence of both the surfactant type and concentration on the volume phase transition of the PNIPAM/water system has been investigated by various methods, such as static and dynamic laser light scattering [l-3 swelling equilibrium [4-6], UV [a], cloud point [6], conductivity [5] and electrophoretic mobility [2], to name but a few. These studies show that the PNIPAM chain or gel network can swell more in the presence of anionic surfactants, and that its volume phase transition temperature increases. The binding of the hydrophobic tail to the PNIPAM chain or gel is believed to be responsible for the additional swelling, but this cannot satisfactorily explain why cationic surfactants with a similar hydrophobic tail have much less effect on swelling whereas nonionic surfactants cause no observable additional swelling over a very wide range of surfactant concentrations. Thus, the detailed structure of the PNIPAM/surfactant complex remains unknown and the insight into this problem is important, as noted by Khokhlov [7], who recently stated: “The theoretical explanation of this pronounced capacity to form self-assemblies in such a complex system is at present lacking; however, it is clear that this fact can have far-reaching technological and biological importance.”

ISSN:0022-2348    

DOI:10.1080/00222349708212394

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Blends of phenolphthalein poly(ether ether sulphone) (PES-C) with a poly-(ether imide) (PEI) in various proportions were prepared by the coprecipitation method. Mechanical properties and morphology of the blends were studied using tensile tests and scanning electron microscopy (SEM). The tensile moduli exhibit positive deviations from simple additivity. Marked positive deviations were also observed for ultimate strength. These results suggest that the PEI/PES-C blends are mechanically compatible. SEM study revealed that the blends are not homogeneous but fine dispersions are obtained. The interfaces between the two phases are well bonded. PES-C and PEI are partially miscible on the segmental level.

ISSN:0022-2348    

DOI:10.1080/00222349708212395

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor