摘要:

AbstractThis paper is the third in a series where the author attempts to provide scientific interpretation for mixing of rubber. Each gum rubber exhibits its own characterstic behavior during mixing. In the previous paper, the behavior was identified with viscoelastic properties and failure. This paper describes characterization of gum rubbers based on viscoelastic properties.Methods of describing deformation are discussed with a proposal to use material functions for the present purpose. Non‐linear viscoelasticity is discussed with a proposal to use a particular linearization scheme. The conventional characterization methods are discussed concerning the limitations and shortcomings of dilute solution methods and the Mooney index. The linearization scheme is applied as the characterization method most suitable for gum rubbers. A number of examples are given to demonstrate the effectiveness of this characterization method in relating the results to molecular architecture. Finally, the discussion covers processability of gum rubbers and their molecular structur

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360201

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA crystalline complex of poly(ethylene oxide) (PEO) andp‐nitrophenol (PNP) was studied by differential scanning calorimetry, X‐ray diffraction, and FTIR spectroscopy, The phase diagram of this system is characterized by a peritectic reaction, and reveals the formation of a new crystal form different from those of PEO, and PNP. The triclinic unit cell of the complex was determined from the X‐ray diffraction patterns of differently oriented samples obtained by mechanical deformations or spherulitic crystallizations. Finally, the molecular packing and the conformation adopted by the PEO chains were determined by FTIR spectroscopy. Polarization measurements have shown that the aromatic rings are very nearly normal to thecparameter (chain axis) and that the 1–4 axes of PNP molecules are parallel to thea*reciprocal parameter (spherulitic growth direction). Finally, a new (t2gt2gt3) conformation is proposed for the PEO chains on the basis of a normal mode analysis and the calculation of the intramolecular

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360202

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractFour blend systems (miscible binary polyester blends) have been examined by positron annihilation lifetime spectroscopy (PALS). The ortho‐Positronium pick off lifetime, τ3, is related to the mean free volume cavity size in these miscible blends. The measured free volume cavity size for the blends is compared to the size predicted from linear additivity of the homopolymers. A negative deviation from linear additivity is observed for τ3in each of the blend systems, and this behaviour is interpreted as a contraction of the mean free volume cavity size due to the changes in molecular packing that occur on blending. The consequence of these free volume results for the mechanical properties of miscible polyester blends is discussed and tested for the polycarbonate/Kodar system. The glass transition data suggest weak specific interactions in the blends; however, the mechanical properties are significantly affected by blend

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360203

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSteady state fluorescence has been used to study the efficiency of nonradiative single energy transfer for naphthalene → naphthalene and naphthalene → anthracene for polyesters and their bichromophoric model compounds. Polyesters containing only naphthalene groups were derived from 2,6‐naphthalene dicarboxylic acid as the rigid unit, and two series of glycols, HO(CH2)mOH and HO(CH2CH2O)n;OH, wherem=2–6 andn=1–4, as flexible spacers. Bichromophoric model compounds were derived from 2‐naphthoic acid and the same glycols. In order to study the transfer for naphthalene → anthracene, a first attempt was made by studying bichromophoric model compounds D(CH2)mA, where D and A denote 2‐naphthoate (donor) and 9‐anthranoate (acceptor) groups, respectively. The fluorescence anisotropy measurements in a solid matrix of glassy poly(methyl methacrylate), for the compounds containing only naphthalene groups, and the simple excitation and emission spectra, for the compounds containing naphthalene and antharacene groups, clearly demonstrate the presence of non‐radiative singlet–singlet energy transfer, the efficiency of which depends mainly onn(orn). A theoretical treatment using the rotational isomeric state model of the conformatin of these molecules has also been performed. The combination of the experiments and the theoretical analysis establishes that the Förster radii are 1.2 and 1.4 nm for the naphthalene → naphthalene transfer in the bichromophoric model compounds and polyesters, respectively, and 1.6 ± 0.2 nm for the naphthalene → anthracene

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360204

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractWe have investigated the interface formation of Ca with poly(p‐phenylene α,α′‐diphenyl vinylene) (PPV‐DP) and poly(p‐phenylene α‐phenyl vinylene) (PPV‐P) using X‐ray photoemission spectroscopy (XPS). Similarly to our earlier findings in metal/PPV interface formation, the O 1s peak shifted toward a lower binding energy as soon as Ca was deposited on to the polymers. This was accompanied by the formation of CaO, suggesting a chemical origin for the O 1s shift. By contrast, the C 1s peak shift toward a lower binding energy was observed relatively later, after about 4 Å of Ca deposition. At the same time, a new C 1s component became noticable at about −1.5 eV relative to the initial C 1s peak. This component signifies the possibility of polymer disruption by the Ca atoms to form CaC species. The C 1s peak shift is attributed to Ca induced surface band bending and barrier formation as in the case of metal/PPV interface formation. The disruption of the polymer may also induce changes in the interface electronic states and contribute to the C 1s peak shift. From the intensity attenuation analysis, we conclude that the initial 15 Å of Ca overlayer is contaminated by the CaO and CaC species and the overlayer is p

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360205

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn this paper a discussion is given of the change of density with time and temperature within a crystal of 192 (CH2)50chains, simulated by molecular dynamics computations at temperatures from 65 to 425 K. The highest temperatures exceed the melting temperature (about 365K). On simulation for times of up to 100 ps the temperature dropped through the melting temperature, permitting the study of the behavior of the crystal during initial melting, followed by limited recrystallization. In these short times only a limited number of chains on the surface can begin to coil and melt conformationally, but there is an indication of a disordering transition. A better comparison with experimental data on density, expansivity and speed of sound is possible.

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360206

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractExperimental evidence in solution and in the solid state suggests that atactic 1,2‐polybutadiene and palladium chloride form coordination complexes with unusual mechanical properties. Ternary phase diagrams with tetrahydrofuran as the solvent highlight regions where gelation is favored relative to precipitation. The strongest evidence for a network structure is based on the facts that (i) solid films swell in heptane, and (ii) infrared spectroscopy identifies a new absorption characteristics of three‐membered rings and dihapto coordination of the olefinic sidegroup in 1,2‐polybutadiene to the metal center in palladium chloride‐bis(acetonitrile). Carbon‐13 solid state NMR spectroscopy suggests that the polymeric palladium complex is a glass when the salt concentration is 4 mol%. NMR linewidth data together with the pulse sequence parameters suggest that the chain backbone of the polymeric palladium complex experiences a significant reduction in molecular mobility which is consistent with diamagnetic glassy materials. Most importantly, the elastic modulus of polybutadiene increases by three orders of magnitude during the transition from rubbery to glassy behavior. This type of mechanical response cannot be explained by a filler effect, crystallite reinforcement, or antiplasticization. Transition‐metal coordination concepts applied to polymeric materials suggest that the enhancement in mechanical properties is a direct consequence of ‘coordination crosslinks’ where the palladium salt bridges different polymer chains. However, palladium‐catalyzed rections of the olefinic sidegroup, generating a chemically crosslinked network, represent a second explanation of the significantly enhanced macroscopic physical properties of 1,2‐polybutadiene in the presence of the transition‐metal salt. Reactive blending via metal‐ligand coordination represents a new mechanism to compatibilize polymeric mixtures that would otherwise e

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360207

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe utility of pulsed‐field gradient (PFG)–heteronuclear multiple bond correlation (HMBC) 2D NMR experiments for characterizing polymer structure is demonstrated. Heteronuclear multiple quantum coherence (HMQC) and HMBC indirect detection experiments provide correlations indicating the presence of one‐bond and two‐or three‐bond connectivities, respectively; this information is vital for polymer structure determination. When HMBC methods are combined with PFG techniques artifacts are eliminated which normally limit the utility of HMBC. The elimination of these artifacts lowers the detection limit by almost two orders of magnitude, making it feasible to detect signals from the small number of repeat units bonded to defect structures, chain ends, branch points and block junctions, despite the presence of much larger resonances from the main‐chain repeat units. Spectra of poly(isobutylene‐b‐butadiene) diblocks and poly(isoprene‐b‐styrene) diblocks are used to illustra

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360208

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractMany attempts to formulate viscoelastic constitutive equations (CEs) for polymeric liquids have resulted in a situation where as many as several tens of popular CEs are in competition nowadays. None of these can describe the available data for simple flows, consistently, and almost all of them display nonphysical instabilities in high Deborah number flows. This paper discusses the most important classes of viscoelastic CEs, present recent results on their stability, recommends some principles of choice of CEs for practical use, and highlights a certain class of CEs for the description of the available set of rheological data for the most well characterized polymers, while satisfying all the stability constraints.

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360209

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractVery small diameter fibers of poly(p‐phenylene terephthalamide) (PPTA) ranging in diameter from 40nm to a few hundreds of nanometers were made by the electrospinning process. The fibers have a circular cross‐section, are birefringent and stable at temperatures greater than 400°C. Electron diffraction patterns obtained from both as‐spun and annealed fibers show meridional and equatorial reflections demonstrating order in the material. The crystal structure and morphology of the fibers were characterized using bright and dark field electron microscopy, electron diffraction and atomic force micr

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360210

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY