摘要:

AbstractMesophase formation of the cellulose/NH3/NH4SCN system has been studied as a function of system composition at 25°C. Compositions for incipience of mesophase formation and for wholly anisotropic phase formation have been determined and relevant phase diagrams constructed. The biphasic gap narrowed when the solvent composition approached 75.5 weight percent NH4SCN and as the cellulose concentration decreased. As solvent composition was changed, the minimum cellulose volume fraction for mesophase formation ranged between 0.02 to 0.045

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300401

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractRaman spectroscopy is shown to be a very powerful method for the study of stress transfer in epoxy composite materials reinforced with high‐performance polyethylene (PE) fibers. We found that the stress transfer length as determined by Raman spectroscopy is substantially shorter for a plasma‐treated fiber than for an untreated one. A shorter stress transfer length indicates stronger interactions between fiber and matrix. Furthermore, the stress transfer length was higher for a PE fiber/epoxy matrix cured at a higher temperat

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300402

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractUsing an elongational flow technique, we have investigated the relationship between the molecular conformational relaxation time and the molecular weight for a solvent whose quality was altered thermally from near θ to a good solvent state. The materials used were closely monodisperse samples of atactic polystyrene. The results show that the relaxation time τ varies with the molecular weight M as τ ∝ M1.5, independent of the solvent quality, a result which apparently is at variance with the observed molecular weight dependence of intrinsic viscosity. Despite this invariance of the molecular weight exponent with solvent quality, our results also show that the coils do expand when the solvent quality was increased in agreement with the mean‐field theory of

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300403

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe dielectric relaxation of 30% crystalline Nylon‐12 of molecular weight 20,000 has been studied at frequencies from 12 Hz to 0.1 MHz and temperatures from 77 to 375 K, and the effect of water on the relaxation spectra has been investigated. Absorbed water increases both the rate and the intensity of both its α‐and β‐relaxation processes and increases the rate but decreases the intensity of its γ‐relaxation process. These results are interpreted in terms of the hydrogen bonding effects of water on localized motions of dipoles in Nylon‐12. The relatively large half‐width of the α‐relaxation, which becomes better resolved at high temperatures, is attributed mainly to the random distribution of crystalline regions in the polymer. It is suggested that water lowers the steric hindrance for the localized mode of dipolar reorientation and causes a redistribution of local sites such that the β‐relaxation process grows at the expe

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300404

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractDried gels of a linear low‐density polyethylene cast from decalin solutions are investigated with particular attention toward structural, thermal, and mechanical properties. The number‐average and weight‐average molecular weights are Mn= 32,000 and Mw= 160,000. In the concentration range 1.00–0.20, the swollen gels exhibit nearly isotropic shrinkage upon drying, which is relevant to an ideal crosslinked network behavior. For the concentrations below 0.20, a strong departure from the isotropic shrinkage indicates that the chains begin to disengage from the macromolecular network owing to the dilution effect. The melting behavior of the dried gels shows that crystallization from solution improves the crystal perfection notably as concerns the more defective crystals. The concomitant decrease of the crystal thickness judged from small‐angle X‐ray scattering is ascribed to a reduction of the surface free energy which is consistent with the build up of regular chain‐folded macroconformations. The drawability of the dried gels is considerably improved with increasing dilution as a result of the gradual disentanglement of the coils prior to the crystallization in solution. But beyond concentration 0.20, the drawability drops because of the loss of intermolecular cohesion when the chains begin to disengage from the network. The drastic change of yield behavior between the melt‐crystallized and solution‐crystallized samples reveals a ductile‐to‐brittle transition in the mechanism of failure of the crystallites at low strain. This phenomenon is related to the improvement of

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300405

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractWide‐angle x‐ray scattering (WAXS) and Raman spectroscopic data show that on both the crystal and molecular levels, a bimodal stress distribution exists in strained high‐performance polyethylene fibers. In part of the crystalline PE the microscopic strain level is high (ca. 70% of macroscopic strain); in the remainder, the microscopic strain level is low (independent of macroscopic strain, ca. 0.4%). During stress relaxation the fraction of highly strained PE decreases with time. WAXS revealed no indication of a change in the a and b unit‐cell dimensions. Furthermore, no indications for stress‐induced formation of monoclinic and/or hexagonal PE and for crystal breaking were found. From the latter it can be deduced that all chains within one crystal are equally strained. The WAXS results are used to calibrate the stress‐induced frequency shifts of

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300406

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe transamidation reaction in a polyamic acid solution has been investigated using size‐exclusion chromatography and low‐angle light scattering. Mixtures of a high‐molecular weight (DP= 150) and a low‐molecular weight (DP= 10) polymer and of the high‐molecular weight polymer with monomer were studied. Mixtures were made at high and low concentrations. The polyamic acid studied is the product of the polycondensation of 3,3′,4,4′‐biphenyltetracarboxylic acid dianhydride (BPDA) with oxydianiline (ODA). In all cases the molecular weight distribution equilibrated with time to a most‐probable distribution with aDPconsistent with the stoichiometry of the mixture. Equilibration required about 2 weeks for mixtures of 10% by weight at ambient temperatures. The effect of addition of a small amount (5%) of low‐molecular weight material to sample of high‐molecular weight is dramatic; forDP= 150 the molecular weight is decreased by more than one‐half. In an entangled solution or melt, this would reduce the viscosity b

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300407

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe electrical conductivity of single crystals of thebis(p‐toluene sulfonate) of 2,4‐hexadiyne‐1,6‐diol (TS) and its polymer (PTS) was measured in a temperature range 77–373 K (to 353 K for TS), dielectric properties were measured from 123 to 283 K. Anomalies of the conductivity and the real part of the complex dielectric permittivity of TS and PTS along the molecular stacking direction at the temperature corresponding to the low‐temperature phase transitions were observed. The dependence of phase transitions on the polymerization conversion of the monomer TS was examined. The phase diagram of the TS‐PTS mixed system wa

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300408

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe plasticization by 4‐decylaniline (4DA) of a microphase‐separated poly(ethyl acrylate) ionomer containing sodium carboxylate groups is examined. Dynamic mechanical thermal analysis, supplemented by differential scanning calorimetry, shows that the matrix and cluster glass transitions (Tg's) in the ionomer are both depressed by ca. 1°C/wt % 4DA; this, in turn, is similar to theTgdepression in the blend of the parent poly(ethyl acrylate) (PEA) with 4DA. There is no evidence of 4DA crystallinity in the blend. Small‐angle x‐ray scattering (SAXS) measurements show that the ionomer peak increases in intensity and decreases in scattering angle with increasing concentration of 4DA in the blend; the corresponding Bragg spacing, initially at 2.3 nm, increases by ca. 0.04 nm/wt % 4DA. These results, supported by preliminary spectroscopic measurements, are attributed to hydrogen bonding interactions between the amine groups of 4DA and the ester groups in PEA and the ionomer, rendering the blend miscible. It is argued that the uniform distribution of 4DA throughout the material plasticizes both phases of the ionomer by adding free volume; this also accounts for the increase in the characteristic spacing detected

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300409

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA solution of polymer chains in the presence of an external electric field is considered. Dipole‐like interactions between polymer chain segment‐vectors and the electric field are assumed to be proportional to the cosine of the angle between the segment‐vector and the direction of the electric field. Parameters characterizing the shape of the chain (i.e., the chain end‐to‐end distance and cross‐section per chain), and parameters describing the local order at the segmental and chain level (i.e., moments of the first and second Legendre polynomials 〈P1〉 and 〈P2〉 are calculated. The optical anisotropy and the molecular shape change induced by the external electric

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300410

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY