摘要:

AbstractMelt‐spun nylon 66 fibers were drawn and subsequently heat treated isothermally and quenched. The heat‐treated fibers were then examined by wide‐and small‐angle x‐ray scattering (WAXS and SAXS), by differential scanning calorimetry (DSC), and by static mechanical testing. These measurements allow one to follow microstructural changes taking place during the course of the heat treatment. WAXS results show that as the treatment progresses, the crystallites become both more perfect and more disoriented with respect to the fiber axis. SAXS results show crystallite thickening. DSC results show that the melting point increases, goes through a maximum, and then decreases as the heat treatment progresses. The tensile modulus decreases with time to an asymptotic level. The changes in crystallite perfection and thickness occur more rapidly than do the changes in crystallite orientation, modulus, and melting point. A model is proposed whereby the two time frames are related to intracrystalline and intercrystalline processes, res

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220501

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractStirrer crystallization of a trans‐1,4‐polyisoprene fraction(M̄n= 3 × 105) was carried out from n‐butyl acetate and from n‐heptane solutions (2% w/v). Fibrous crystals in the ß form were obtained at temperatures of 46‐48°C in the two solvents, respectively. At 36‐46°C from n‐butyl acetate and 25‐35°C from n‐heptane lamellar crystallization took place leading predominantly to the α form. Melting endotherms and densities for various samples were obtained. The maximumTENDO for α was 74°C and for ß 79°C and the maximum weight fraction crystallinity for ß was 0.78. The stability of performed α nuclei in n‐butyl acetate and n‐heptane using a fraction withM̄n= 2.5 × 105was monitored as a function of temperature. The dissolution temperature of fibrous ß‐TPI with the maximumTENDO was measured in 13 liquids and the results analyzed in terms of the Flory‐Huggins parameter. The heats of fusion for the α and ß forms, obtained by extrapolation of heat of fusion versus change in specific volume, were found to be 8.0 and 10 kJ mol−1,respectively. The pressure coefficients of the melting temperature were calculated to be 38 and 43 K kbar−1and the fold‐surface free energies recalculated to be 42 ± 1 and 53 ± 1 erg cm−2for the α and ß forms, respectively. The number of monomer units per average noncrystalline chain traverse for

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220502

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe orientational drawing of polymers is known to be terminated because of sample rupture. The limiting draw ratio λlimreached may be different (either large or small) depending on the polymer and the actual drawing conditions. The purpose of the present work is to identify the change of supermolecular structure of polymer fibers which results in the termination of orientational drawing. Small‐and wide‐angle x‐ray diffraction were used to study the variation of geometrical parameters of this structure with increasing draw ratio λ. The geometrical parameters discussed are the dispersions (fluctuation) of long periods and of longitudinal sizes of crystalline as well as amorphous regions. In this study we used fibers of poly(vinyl alcohol), poly(ε‐caprolactam), polyoxymethylene, and poly(4,4′‐diphenyloxide) pyromellitimide. It is found that the long period dispersion of these polymers, drawn under different conditions, increases to approximately the same value for different samples drawn to the limit, this relative standard deviation δLof long periods being 0.30‐0.40. It is also found that the crystallite size dispersion does not increase with increasing λ; the increase of λLis due to increasing dispersion of the amorphous region lengths. For poly(vinyl alcohol) fibers drawn to the limit under different conditions and which have different λlim, the relative standard deviation of the sizes of amorphous regions δAturned out to be about the same (ca. 0.60). The latter evidence gives grounds to suggest that the rupture of polymers under drawing is associated with reaching a high degree of amorphous region size dispersion. In those regions which are considerably below the average size there probably will appear local overstress and molecular ruptures because the relative deformation of these regions is much larger than that of the adjacent regions in the cross

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220503

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractSpectroscopic experiments were carried out to directly measure the electric‐field‐induced microstructural changes in PVF2at high temperature (65°C). We found, in comparison with roomtemperature measurements, that the reduction of the coercive field is directly related to faster dipolar orientation at this temperature. Furthermore, the α to β or δ phase transformation can take place at a much faster rate and lower field strength than has been previously reported either theoretically experim

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220504

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe linear thermal expansion coefficients α of three isotropic samples (crystallinity v = 0.42‐0.8) and one oriented sample (v = 0.8, draw ratio 11) of polyethylene have been measured between 2 and 100 K. Together with our previous measurements at high temperatures, these data provide general patterns for the crystallinity and orientation dependence over a wide temperature range. α varies only slightly with crystallinity from 50 to 120 K, but at higher and lower temperatures, it increases significantly with decreasing crystallinity. The increase at high temperature arises from segmental motion in the amorphous regions, while the large increase near 5 K is similar to that observed in many glasses. The tranverse expansion coefficient of the oriented sample is 40‐100% higher than the values for isotropic polyethylene, but the axial expansion coefficient is much smaller and is negative over the entire temperature range. The values of these coefficients are quite close to those for the polyethylene crystal, a feature readily understood in terms of existing models. However, as a result of the much larger elastic anisotropy of the crystal, the Grüneisen parameters (especially the axial Grüneisen parameters) of these two types of polyethylene have rather different

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220505

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA theory is proposed for the rod to coil transition in polydiacetylene 4BCMU and related polymers which is based on the hypothesis that the high‐temperature (yellow) phase consists predominantly of the cis structure, while the low‐temperature (red) phase is trans. Because the occurrence of a cis‐trans interface is energetically costly, the correlation length for either isomer remains long and the transition is sharp, much like the helix‐coil transition in the theory of Zimm and Bragg. The transition is driven by the higher entropy of the cis isomer, which is free to coil, unlike the trans or butatriene forms. The theory gives excellent agreement with optical absorption measurements and is consistent with all other experimental data for this

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220506

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractWe use Zimm's single‐contact approximation to investigate the concentration dependence of the first cumulant for partially labeled chains in dilute solutions. This approximation allows us to express interchain properties (such as the interference part of the generalized mobility) in terms of static structure factors, which are then modeled using a Gaussian chain model. We present numerical results for three specific labeling sequence

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220507

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAtactic poly(vinyl acetate) prepared in a free‐radical polymerization was crosslinked by means of benzoyl peroxide. The resulting elastomeric networks were studied in elongation, both unswollen and swollen with triethylbenzene, over the range 0–90°C. The most important experimental results obtained were values of the network birefringence, which is negative, as was recently also found to be the case for networks of atactic poly(methyl acrylate).Calculations carried out to interpret the birefringence were based on Monte Carlo simulations of the atactic structure, and on the rotational isomeric‐state theory of chain configurations. The agreement between theory and experiment was very good, in fact much better than has usually been observed for other polymers studied t

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220508

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe differential equation that describes the mass balance of a solvent which diffuses in a shrinking or swelling body is transformed in order to fix the domain of integration and a numerical solution is given. The numerical results obtained differ significantly from the solution of the equation without volume change commonly used in literature. Hence, the new equation could affect substantially the fields of drying, dyeing ion exchange, diffusion in polymers, and solid‐liquid extractio

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220509

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA simple model for calculating the fracture process for a single extended‐chain molecule such as polyethylene is considered. The model consists of a chain of N coupled Morse oscillators. There exists a critical overall extension ΔLcbelow which the fracture is energetically unfavorable but above which fracture is favored both energetically and kinetically. This elongation ΔLcscales asN1/2. For the critically stretched chain, the activation energy for rupture increases with N. Long chains must be stretched beyond this critical value to fail within experimentally meaningful times. Chains of all lengths subjected to the same force will fail with the same activation energy, provided this force is large enough to stretch each chain to ΔL>ΔLc. Observed activation energies are less than 1/3De, whereDeis the bond e

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220510

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY