摘要:

AbstractMolecular motions in mixtures of the side chain polymer—poly(vinyl acetate) and dibuthyl phthalate were studied as a functionof polymer concentration and temperature using the technique of paramagnetic resonance (EPR). When the small spherical probe tempol (TPL) was used, we were able to approximate the observed EPR spectrum with a simulation using a single rotational correlation time τ. The peviously developed Grest–Cohen all‐temperature model matched the Arrhenius polts. The EPR spectra from a cigar‐shaped cholestane (COL) probe could not be adequately matched by single τ simulation when the polymer was at temperatures somewhat above the glass to rubber transition temperature (Tg). Points corresponding to these temperatures were left of the Arrhenius plot and a discontinuity was observed where the gap in the data occurred. As the concentration of plasticizer was increased, we found that the discontinuity became less steep, but the τ at which the gap occurs was always ≈ 10−8. The spectra observed at the temperature region of the gap were approximately 50–50 composites of experimental spectra observed at ± K. In both the TPL and COL cases, there was evidence of the existence of multiple correlation times. Preliminary studies of other polymers, both with and without side chains, also indicated the existence of the gap when COL is used as the probe. © 1993 Jo

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311301

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe application of spin‐polarized neutrons with spin polarization analysis to study diffraction patterns from polymers is discussed. The experimental separation of the coherent and incoherent parts of the scattering coupled with the use of the internal standard resulted in the quantitative analysis of the purely coherent scattering from unfunctionalized and functionalized polystyrene in terms of absolute units. This allowed us to model the scattering curves in terms of paracrystallinity. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311302

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe tracer diffusion of 3‐, 4‐, and 12‐arm polystyrene (PS) stars in poly(vinyl methyl ether) (PVME) gels has been measured by dynamic light scattering (DLS). The intensity correlation functions were analyzed by two methods. One was that employed previously in a DLS study of linear PS diffusion in PVME gels [N. A. Rotstein and T. P. Lodge,Macromolecules, Vol. 24. p. 1316 (1992)], and the other was based on consideration of possible nonergodicity effects [P. N. Pusey and W. van Megen,Physica A, Vol. 157, p. 705 (1990)]. Both methods gave equivalent results, suggesting that nonergodicity plays a small role in this system. This conclusion is not unreasonable, given that the PVME gels are almost isorefractive with the solvent (toluene), and that the signal is dominated by scattering from the PS chains. The resulting star diffusivities are consistently less than or equal to those for linear probes of comparable size, with the difference increasing with molecular weight. The diffusivities are also less than or equal to those obtained for the same stars in PVME solutions. A weak dependence on the number of arms is also observed. Finally, the mobility of a given star in a gel is much more sensitive to variations in the average molecular weight between cross‐links than is the mobility of a linear chain. All of these features in the data are broadly consistent with the reptation hypothesis. © 1993 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311303

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractAn unconstrained polymethylene crystal, consisting of 9600 CH2groups, in which each CH2is permitted to carry out stretching, bending, and torsional motion, has been studied at various temperatures using molecular dynamics simulations. Information about the atomistic details of the dynamics and structure of these crystals is presented. A significant disorder exists at tempratures well below the melting point. Close to melting, the disordered crystals have about 2% ofgauchebonds that are distributed mainly at positions close to the surface of the crystal. The major disorder consists, however, of a collective twisting of the chains leading to a hexagonal crystal structure. The hexagonal structure of the symmetric motifs is caused by a dynamic multidomain arrangement of the chains. © 1993 John Wiley&Sons, Inc

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311304

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

Abstract4‐Acetoxy 4′‐carboxy biphenyl has been polymerized from solution, the bulk melt, and in constrained thin films, all below the melting point of the monomer as measured by differential scanning calorimetry (DSC). An isothermal sublimation–recrystallization–melting (and chemical change)–polymerization–crystallization process is proposed. From solution and in the thin films, single crystals consisting of ca. 100 Å thick lamellae are observed, with evidence for monomer addition–reaction on the end (top and bottom) surfaces. The bulk samples are fibrous, the “fibers” consisting of whisker‐like single crystals. The polymer is highly heat and radiation (electron beam) resistant, with numerous successive electron diffraction (ED) patterns from the same crystal or sheared sample permitting comparison of the changes in ED patterns with transitions seen by DSC at ca. 350, 530, and 590°C. Phase I (a= 7.8,b= 5.5,c= 10.8 Å), a possible phase II (a= 15.6,b= 3.6 Åc= unknown), and a phase III (a= 9.0,b= 5.2 = √3a,c= 10.8 Å). Phases I and II are seen in samples polymerized at temperatures at and below 310°C; phase III is observed in samples polymerized at and above 350°C and in sheared sample

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311305

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractPoly[(1,7‐dihydrobenzo[1,2‐d:4,5‐d′] diimidazole‐2,6‐diyl)‐2‐(2‐sulfo)‐p‐phenylene], a conjugated rigid‐rod polymer, was derivatized with pendants of propane‐sulfonated ionomers. The derivatized rigid‐rod polymer was soluble in aprotic solvents as well as in water for isotropic solutions that were processed into isotropic films. Direct‐current electrical conductivity σ of the films was measured using the four‐probe technique. Room‐temperature σ as high as 2.9 × 10−4S/cm was achieved on pristine isotropic films without using dopants. When the rigid‐rod polymer concentration exceeded 25 wt %, the isotropic solution could be transformed into a liquid‐crystalline solution that allowed deformations to be applied to produce anisotropic films. Significant increase in σ was obtained in a sheared film alongboththe parallel direction (∥) and the transverse direction (⊥) with a σ∥/σ⊥= 5. Additionally, enhanced σ was realized in films heat‐treated at about 100°C, in the derivatized polymer with higher molecular weight from dialysis, and in substituting the sulfonated ion Na+by H+in the pendants of the polymers. Constant‐voltage measurements were applied to the polymers to monitor the σ stability for ascertaining the nature of the conductivity. No electronic contribution in σ was detected. Instead, a monotonically decreasing σ was consistently observed

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311306

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractWaveguide coupling measurements of polymers have largely concentrated on the application of mode analysis to the study of thin supported films (such as spin coatings). The use of prism coupling to study thick, freestanding polymer films, however, has not been reported. In this paper, the ability of prism coupling to characterize the three‐dimensional optical properties of thick, freestanding polymer films and sheets is demonstrated. A modified prism coupling procedure is described that allows the determination ofall threeprincipal refractive indices in thick, three‐dimensionally anisotropic freestanding films. A Metricon prism coupler is used in a manner similar to an Abbé refractometer for the measurement of isotactic polypropylene, poly(ethylene terephthalate), PMDA‐ODA polyimide, and poly(phenylene sulfide). Three series of PMDA‐ODA films are also investigated in this study. The first series has been drawn to different extensions from three‐dimensionally random films. The second series has random orientation in the plane of the film but different degrees of planarity with respect to the through direction. The third series are commercial films of varying thickness. These three series of films are compared as to the optical an‐isotropy that is developed from the three different fabrication processes. © 1993 John Wi

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311307

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractInvestigations on aluminum chloride‐mediated solubilization of poly(p‐phenylenebenzo‐bisthiazole), PBZT, in nitromethane revealed that, in general, dilute solutions of the polymer prepared in nitromethane with a large molar excess of the Lewis acid with respect to PBZT were relatively stable and thus suitable for processing into films and coatings via regeneration with hydroxylic nosolvents while polymer solutions with minimum stoichiometrically required (PBZT:AlCl3molar ratio 1:4) or marginal molar excess of AlCl3relative to PBZT tended to gel during handling. Structural studies on polymer–Lewis acid complex solutions were performed using1H and27Al NMR.1H NMR of the protonated structure of the model compound 2,6‐diphenylbenzo [1,2‐d:4,5‐d′] bisthiazole was useful for confirming the1H NMR assignments of PBZT‐AlCl3complex solution in CD3NO2.27Al NMR was particularly useful in probing the different tetrahedrally coordinated environments of the Al nucleus in the polymer solution, pointing to a complexation interaction between the polymer molecule and the Lewis acid and also between the solvent and the Lewis acid. Direct evidence in the solid state for the presence of a reversible electron donor–acceptor complex (EDA complex) was obtained from FTIR spectra of complexed films, isolated and handled in an inert atmosphere. The structural changes upon PBZT complexation caused significant frequencly shifts in both aromatic as well as heteroring stretching modes relative to PBZT itself, and intensity variations indicative of changes in the resonance configuration between the 1,4‐phenylene moiety and the aromatic heterocyclic ring were also observed upon complexation. A preliminary comparison between the pristine PBZT fibers and regenerated PBZT by dilute solution viscometry indicates that the process results, to some extent, in polymer degradation leading to a decrease in the molecular weight of the polymer © 199

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311308

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractWe have studied the conformation and coefficient of thermal expansion in the poly(p‐phenylene) oligomerp‐sexiphenyl (C36H26) by molecular dynamics simulations. Studies of the backbone phenyl–phenyl torsion angle in a simulatedp‐sexiphenyl crystal at room temperature indicate the presence of torsional librations of approximately ±20°. Further analysis of the phenyl–phenyl backbone torsion angle in less closely packed regions of the simulated crystal (crystal ends) indicate the presence of 180° phenyl ring flips, in agreement with solid‐state deuterium NMR data on poly(p‐phenylene oligomers). The linear coefficient of thermal expansion was also calculated and found to be negative, in qualitative agreement with experimental data on rigid‐rod compounds. © 1993 J

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311309

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe nonlinear susceptibilities (χ(2)33, χ(2)31), and the refractive index anisotropy, of a main chain accordion polymer, BCSC (see the text for the complete chemical formula), have been measured by the techniques of second harmonic generation (SHG) and waveguiding. A large birefringence, which is induced in the BCSC film by the spin‐coating process, is almost removed by electric field poling. Our results demonstrate the fundamental difference between the birefringence associated with quadrupolar orientational order and the dipolar order associated with SHG. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311310

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY