ISSN:0887-6266    

DOI:10.1002/polb.1993.090310101

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe structure of polyacetylene–polyisoprene block copolymer solutions prepared by a modified anionic to Zeigler‐Natta method is reprted. Small‐angle x‐ray scattering results are consistent with formation of wormlike micelles, which arise mainly from interactions between the polyacetylene blocks of the copolymer in solution at room temperature. Aggrgation of the wormlike micelle can be described in terms of fractal geometry. I2‐doping produces marked changes in the optical spectrum of the acetylenic block and the small‐angle scattering indicates a change in polymer aggregation to a lamellar form. It is concluded that micellar structure is the natural morphology for solutions and gels of conducting polyacetylene–polyisoprene copolymers and that this persists into the solid state. Thus, conduction mechanisms for these polymers may bear re‐examination using micelles as the structural basis. © 1993 John

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310102

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe photoelastic properties of textured polymer composites are considered for the high deformation limit. Photoelasticity equations for incompressible polymers are derived in the correlation function theory approximation. It is shown that the birefringence may be zero for critical stretching across the texture axis. This effect can be used to measure the dispersion of shear moduli of polymer composites. © 1993 John Wiley&Sons, Inc

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310103

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractCharacteristic changes in the surface topography due to UV laser treatment are of high significance for the determination of material destruction thresholds and surface structure development. E.g. irradiation of poly(ethylene terephthalate) (PET) film with pulsed UV laser light of 248 nm modifies the smoth surface of the polymer into a well oriented structured surface. The development of these structures were studied with scanning tunneling microscopy (STM) and high resolution optical profilometry. Three dimensional data of the surface were taken from the samples after each laser pulse. A change of topographic data was found in relation to fluence and number of pulses applied. © 1993 John Wilcy&Sons, Inc

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310104

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractDiffusion of 2,4‐dinitroaniline and three nonionic azo dyes in Nylon‐6 film was studied by analysis of the concentration‐distance curves (profiles) of penetrants in the polymer. Actual diffusivitiesD(c)of penetrants in polymer, diffusion coefficients as a function of the concentrationCfof penetrant in polymer, were calculated from the profile. It was found thatD(c)is almost constant or decreases gradually with decreasingCfin the range of high‐mediumCfbut decreases appreciably with decreasingCfat lowCf. The change inD(c)withCfwas explained in terms of the dual‐mode sorption‐diffusion model. The penetrants diffuse in the polymer as two distinct species, i.e., a dissolved species and an adsorbed species. The former is the penetrant taken up by the polymer by a partition mechanism (dissolved species) and the latter is that taken up by Langmuir sorption (adsorbed species). The actual diffusivityDP(c)of the dissolved species decreases with decreasingCf. While the actual diffusivityDL(c)of the adsorbed species normally increases gradually with decreasingCf.DP(c)is usually larger thanDL(c). © 1993 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310105

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractFilms of polystyrene–polybutadiene–polystyrene (PS/PB/PS) triblock copolymer and polystyrene‐poly(ethylene/propylene) (PS/PEP) diblock copolymer were cast from toluene solutions subjected to hydrodynamic flow at room temperature using a device based on a novel casting method we term ‘roll‐casting.’ Polymer solutions were rolled between two corotating eccentric cylinders while at the same time the solvent was removed at a controlled rate. As the solvent evaporated, the block copolymers microphase separated into globallyorientedstructures. A discussion of the flow field that develops during roll‐casting is presented and specific attention is given to the importance of the shear and elongation rates present. For the triblock and diblock, respectively, the processed structures consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix, and unidirectional lamellae of alternating polystyrene and polyethylene/propylene. Small‐angle x‐ray scattering (SAXS) and transmission electron microscopy (TEM) indicated the near single‐crystal structure both types of films. SAXS also showed the styrene cylinders and the alternating lamellae to be packed closer together in roll‐cast films than in simple quiescently cast films. A molecular orientation mechanism is proposed to describe both these results as well as the changes in packing and in macroscopic sample dimensions measured after complete solvent evaporation and after sample annealing. © 199

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310106

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe influence of thermal history on the dynamic mechanical behavior in the alpha relaxation region of high‐density polyethylene (HDPE) is predicted using computer modeling. The model considers the mechanical alpha relaxation as a succession of cooperative single movements occurring within the defect region of the crystal lattice that finally produce a relative displacement between lamellae. A distribution function of the number of such single steps is postulated considering topological properties of the sample: branch content and molecular weight. To carry out the simulation, the model uses the spectrum of the sample subjected to fast cooling as a reference system. In addition, the crystallinity and the segregated material content for the particular thermal history of the object of study are also required. Loss modulus spectra are generated using balance of energy considerations, and a few examples are presented together with several experimental results. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310107

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractPolymer crystallization and melting under nonisothermal conditions are investigated by means of an extended version of the two‐dimensional Sadler / Gilmer pinning model. In particular, the case of a constant heating rate is simulated. Lamellar thickening and eventual melting are studied for a range of heating rates and initial temperatures. An approach to equilibrium (i.e. infinite thickness atTom) by slowing down the heating rate is found to be more than exponentially suppressed. Similarities with heating experiments on polyethylene and PEEK are demonstrated. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310108

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractAn evaluation of free‐volume theories for solvent self‐diffusion is carried out using recent comprehensive data sets for penetrant self‐diffusion in polymer solutions. Different theories are compared, and free‐volume theories in the prediction of penetrant self‐diffusion coefficients in glassy polymer systems is also evaluated. © 1993 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310109

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractWe propose a new method of calculating elastic modulus and atomic displacements of a stretched polymer chain. We use a stretched Cartesian coordinate system and a stretched B matrix defined by the Cartesian displacement components of the bonds to express the potential energy matrixFxfor stretching. The method is used to calculate elastic moduli of planar‐zigzag‐chain vinyl polymers and helical‐chain isotactic polypropylene and the atomic displacements of their skeleton and side groups. The skeletal displacements of planar‐zigzag‐chain polymers are about ten times larger than those of the side groups and reverse displacements of the two adjacent skeletal units occur in the direction perpendicular to the stretching direction along the fiber axis. In the case of isotactic polypropylene, the methyl group has more effect than the torsional change around the CC bond on the skeletal deformation. © 1993 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310110

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY