摘要:

AbstractThis paper continues an investigation into the ethylene–vinyl chloride copolymers prepared by partial reduction of poly(vinyl chloride). The infrared spectra of the copolymers have been obtained and the individual resonances assigned. Each infrared band has been quantitatively analyzed in terms of peak position (cm−1) and intensity, and correlations with the sequence microstructure (dyad, triads, etc.) have been determined. The infrared resonances have been found to be sensitive to long sequences; i.e., (V)xor (E)xwherex≥ 10. Sequences of up to 10–15 monomer units were seen to affect the position (cm−1) and intensity of CH stretching and bending frequencies. Methylene rocking bands between 850 and 700 cm−1were observed to be sequence dependent with V(E)xV resonanting at 860, 750, or 730 cm−1forx= 0, 1 and 2, or ≥3, respectively. The CCl stretching resonances, which are well known for their conformational complexity in pure PVC, were found to be dominated by sequence length effects reducing to two bands at 665 and 610 cm−1characteristic of and isolated CHCl u

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240801

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractWhen polymeric materials doped with nitroxides of the 2,2,6,6‐tetramethylpiperidine type are exposed to light, the nitroxide concentration decreases. The two mechanisms for the decrease of the nitroxide are the reaction of nitroxide with free radicals produced during photolysis of the polymer to form amino ethers and the abstraction of hydrogen atoms by excited‐state nitroxides to form hydroxyl amines. Excited‐state nitroxides can be formed in two ways: by direct absorption and by energy transfer. In this paper, the effect of energy transfer on the rate of decay of the nitroxide signal is studied, and measurements of nitroxide decay are used to probe energy transfer in crosslinked polymeric coatings. A simple kinetic scheme is used to interpret nitroxide decay during photolysis of both solutions and polymers containing benzophenone. These results are used to show that the slope of the line relating nitroxide decay rate to nitroxide concentration is essentially determined by energy transfer from a coating‐based chromophore to nitroxide. The nitroxide decay assay is also used to study the effectiveness of a benzotriazole ultraviolet light absorber as a q

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240802

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractWhen a melt‐spun poly(ethylene terephthalate) (PET) fiber is heat treated at a temperature above its glass transition temperature, the relative rates at which the crystallization and major orientational relaxation processes occur have been shown to have a pronounced effect on the structure of the fiber and its deformability. The present study describes the consequences of this aspect, with examples from drawing of melt‐spun PET fibers subsequent to their crystallization by thermal annealing. Additional features of the highly ordered PET fibers which can be produced through a combination of oriented crystallization and drawing at high temperatures are also gi

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240803

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe thermal behavior and crystal transformation of poly(p‐benzamide) are reported. Modification I contains both solvent (N,N‐dimethylacetamide) and LiCl in its crystal lattice. Modification II is likely to form a complex crystal with LiCl, whereas crystalline modification III contains neither solvent nor LiCl in its unit cell. The crystal transformation temperature from modification I to II is 214°C, and the crystal–nematic transition temperatures of modification II and III are 475 and 544°C, respectively. Modification III can be obtained from II by heating above 475°C and cooling, or by washing with water. It can also be obtained from modification I by washing with water and a

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240804

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractDifferences in the temperature and pressure dependences of the relaxation times of a slow diffusional process and the α structural relaxation pose an interesting problem. This feature, observed by dynamic light scattering in amorphous poly(phenylmethyl siloxane), is related to another basic feature of lack of thermorheological simplicity discovered by Plazek in polystyrene, poly(vinyl acetate), and amorphous polypropylene. A quantitative explanation based on the predictions of a general coupling theory of relaxations has been found. The coupling theory also predicts the Kohlrausch fractional exponential time correlation function exp[−(tτ*)1−n] at long times, as observed by photon correlation spectroscopy, and crossover to an exponential time dependence exp–(t/τ0) at short times, as frequently assumed in Brillouin scattering. An additional relation between τ*and τ0predicted by the theory is confirmed also by the experim

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240805

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe Tennessee Eastman copolyester of poly(ethylene terephthalate) with 60 mol %p‐oxybenzoate units was spun with various capillaries using a constant shear rate at the wall. Variables examined were the length‐to‐diameter ratioL/Dof the capillary, the spin draw ratioVf/V0, and the spinning temperature. Fibers spun at 260°C showed improved homogeneity of orientation through the cross section, better crystallite orientation, and higher initial moduli asL/Dwas increased. The spin draw ratio required to optimize these fiber properties decreases asL/Dis increased. For example, whenL/D= 49.44, the initial modulus has nearly reached its plateau value at a spin draw ratio of 10. However, in contrast to the results of Sugiyama, Lewis, White, and Fellers, we find thatsomespin draw is always required to optimize fiber properties. Fibers spun with a spin draw ratio of approximately unity showed very poor crystallite orientation and initial moduli. It is suggested that loss of orientation under these conditions may be due to the different velocity profiles in the spinneret and in the solidifed fiber. Fibers were also spun at five temperatures using a capillary havingL/D= 49.44. Shear in the capillary is more effective in introducing orientation when the spinning temperature is 260°C or above. At spinning temperatures of 240 and 250°C, the initial modulus increases more slowly with spin draw ratio, and appears to have a lower plateau value. Acierno, La Mantia, Polizzotti, Ciferri, and Valenti spun the same polymer under conditions in which essentially all the orientation was introduced by spin draw. They used a very low extrusion velocity at the spinneret, a smallL/D, and spin draw ratios up to 3000. They reported that the initial modulus increased withdecreasingspinning temperature, in contrast to our results. Thus the optimum spinning conditions may depend upon whether most of the orientation is introduced by shear in the capillary, or by a high spin dr

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240806

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThermoluminescence (TL) emission from low‐density polyethylene has been investigated. The glow curves of gas‐free samples x‐irradiated at −190°C and heated to room temperature were found to contain three peaks numbered I, II, and III in order of increasing temperature, in agreement with earlier results. The sites of all traps are accessible to absorbed gases; in the presence of air, O2, N2or Ar, “gas” traps are formed, resulting in the appearance of an additional peak IV in the glow curve at a temperature between peaks I and II, large reductions in the intensities of peaks II and III, and various changes in peak I. The peak I, II, and III traps are formed from particular chain configurations occurring in the chain‐fold regions of the samples, these configurations being broken up by different forms of molecular motion within the chains. It is unlikely that the peak IV traps are just the gas molecules themselves; they are probably formed from new chain configurations occurring in the amorphous regions of the samples in the presence of the gas, the properties of the gas influencing the associated TL intensity and emission temperature. These traps are also broken up by molecular motion. The samples can be divided into two main types, differing mainly in the height of peak I relative to peak II, which is of nearly constant intensity in all samples. We suggest that two types of trap which are not interconvertible are associated with peak I, and that the dominant type in a given sample depends on the fine details of the sample fabri

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240807

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThermoreversible gels of cellulose acetate can be obtained by cooling concentrated cellulose acetate solutions in solvent‐nonsolvent mixtures of dioxane and water. Upon heating the gels, endothermic effects were observed with differential scanning calorimetry. The heat effects are ascribed to the melting of a crystalline phase consisting of cellulose triacetate units. The endothermic peaks appear only after long aging periods of up to several days. Melting points generally decrease and heats of melting increase with increasing polymer concentration and with increasing nonsolvent content. The maximum degree of crystallinity is estimated as 8%. The kinetic effects of varying the water content in the solvent mixture are discusse

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240808

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe Doi‐Edwards theory of polymer melts, extended to include relaxation processes associated with chain‐length equilibration, is used to make quantitative predictions of a discontinuity in the flow curve of a monodisperse melt in a capillary. A fluid interface between regions of high and low deformation rates is found to propagate from the former into the latter. Our results for the “spurt” and its hysteresis compare favorably with experiment using a molecular weight dependence of the ratio of “reptation time” (Td) to “equilibration time” (Teq) in agreement with that determined from nonlinear st

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240809

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractA method of correcting gravimetric data for diffusion through the sample edges to obtain true diffusion coefficients is presented. This method is compared with existing methods to show that it has the best accuracy for thick slab or cubic sample geometries.

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240810

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY