摘要:

AbstractMicrostructural changes occurring during the process of crystallization in as‐spun poly(ethylene terephthalate) (PET) have been monitored using wide‐ and small‐angle X‐ray scattering, optical birefringence, shrinkage measurements, and specific gravity.Shrinkage and birefringence results show a competition between two processes: chain re‐coiling on the one hand and crystallization on the other hand. A consistent correlation among WAXS, SAXS, shrinkage, and birefringence results is demonstrated. SAXS data show a fibrillar morphology. On the basis of WAXS results, the crystallization is envisioned as a two stage process: first, the formation of defective fibrils, and then the formation of more perfect crystals. WAXS results also demonstrate a remelting phenomenon in samples which have experienced positive

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241201

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractSmall‐ and wide‐angle X‐ray scattering (SAXS and WAXS), shrinkage, and density experiments were performed on poly(butylene terephthalate) fibers which had been isothermally crystallized at different temperatures, and at constant tension, for times ranging from 100 to 1050 ms.A consistent correlation among WAXS, SAXS, and the kinetic results is demonstrated. Shrinkage results show that the crystallization process prevails over the chain‐re‐coiling process. Density measurements show that the rate of crystallization increases with temperature. Pinhole X‐ray photos show that the orientation of the chains within the crystals remains constant with time and temperature. WAXS diffractometer scans show the development of wide‐angle Bragg peaks.SAXS shows the development of small‐angle Bragg peaks, as the annealing time is increased. The two‐lobe arced pattern is the characteristic pattern. The value for long spacing ranged from 100 to 120 Å, increasin

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241202

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractPVA films (30–45 μm thickness) were prepared by casting. dc electrical measurements were done over the temperature range 293–353 K. Two different conduction mechanisms are suggested. The first one is ohmic and extends to 303 K. Above this temperature a space‐charge‐limited conduction mechanism, with protons as charge carriers, predominates. Dependences of the voltage‐reversion current temperature and field were investigated and were attributed to a clean‐up effect of charge carriers. The variance in the activation energy, calculated from the conductivity curves and from the mobility curves, led to a discussion of the origin of the charge carriers. No change in conductivity was observed for the PVA films irradiated with UV (of wavelength 365 nm) at 303 K, i.e., PVA is a photostable material under thes

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241203

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractFourier‐transform infrared spectroscopy has been used for the study of orientation of pure and plasticized PVC. The results show that orientation is independent of experimental conditions (temperature, strain rate, plasticizer) in the homogeneous deformation range. Such behavior is explained by the existence of a fringe micellar‐type network with physical crosslinks. The network is partially destroyed during stretching. Furthermore, the orientation of the carbonyl group of the plasticizer is connected with PVC chain orientat

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241204

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractA method by which the occurrence of a secondary relaxation can be deduced from the isochronal dielectric and mechanical loss data of amorphous and crystalline materials is given. The method eliminates the complexity arising from the frequency‐independent, temperature‐dependent background loss in solids.It is shown that the relaxation rate measured at a fixed frequency by varying the temperature substantially differs from that measured at a fixed temperature by varying the frequency when the strength of the relaxation is temperature dependent. This discrepancy leads to a different value of activation energy and of preexponential factor when the strength increases with temperature. The results are discussed in terms of the temperature dependence of the strength of relaxation and its distribution parameter.The method of analysis has been applied to the data for a molecular and a polymeric glass and shows the occurrence of a β process which is otherwise not detected in their tan β isochrones. Experimental data on a wide variety of glasses also show that the activation energies and relaxation rates obtained from isochrones differ from those obtained from the isothermal spe

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241205

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe influence of the chain expansion produced by excluded volume on the mean‐square optical anisotropy has been studied in six types of polymers. The mean‐square optical anistropy for a specified configuration is calculated using the valence optical scheme. Realistic rotational isomeric state models are used for the configurational statistics of the unperturbed chains. Excluded volume is introduced by hard sphere interactions. Results obtained with chains of 100, 200, 300, and 400 bonds permit extrapolation to the behavior expected for much longer chains. The mean‐square optical anisotropy of polyethylene is insensitive to excluded volume. A similar conclusion was obtained several years ago in a study of chains confined to a tetrahedral lattice and weighted in a manner appropriate for the short‐range interactions in polyethylene.2Different behavior is seen in poly(vinyl chloride), poly(vinyl bromide), polystyrene, poly(p‐chlorostyrene), and poly(p‐bromostyrene). The mean‐square optical anisotropy of these five vinyl polymers is sensitive to the imposition of excluded volume if the stereochemical composition is exclusively racemic. Much smaller effects are seen in meso chains and in chains with Bernoullian statistics and an equal probability for meso and

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241206

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractA series of polyurethane block copolymers based on hydroxybutyl terminated poly(chloropropylmethyl‐dimethylsiloxane) and poly(tetramethylene oxide) soft segments of molecular weights 2100 and 2000, respectively, were synthesized. The hard segments consisted of 4,4′‐methylenediphenylene diisocyanate (MDI) that was chain extended with either 1,4‐butanediol (BD) or N‐methyldiethanolamine (MDEA). The materials chain extended with MDEA were ionized using 1,3‐propane sultone. The weight fraction of the hard segments was in the range 0.30–0.45. The effect of mixed soft segments, chain extenders, and zwitterionization on the extent of phase separation and physical properties was studied by utilizing differential scanning calorimetry and dynamic mechanical, stress‐strain, and Fourier Transform Infrared spectroscopy experiments. All of these short segment block copolymers showed nearly complete phase separation. The zwitterionomer materials exhibited ionic aggregation within the hard domains. Although hard segment crystallinity or ionic aggregation did not affect the morphology, hard domain cohesion was important in determining the tensile and viscoelastic properties of t

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241207

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractA method of obtaining the scattering spectrum that bypasses the need to solve for the configurational distribution function of the macromolecules is presented. It involves the direct calculation of averages that appear in the structure factor expression. Application of the method to Rouse coils recovers Pecora's classical results. The method is applied to obtain the coherent spectrum of a solution of “encapsulated” dumbbells for which the configurational distribution is not availa

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241208

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractHeat capacities were measured for poly(4‐methylstyrene) [300–500K], poly(4‐fluorostyrene) [130–350K], poly(4‐chlorostyrene) [300–550K], poly(4‐bromostyrene) [300–550K], poly(4‐iodostyrene) [300–550K] and poly(styrene‐co‐divinylbenzene) with 1, 2, 4, 8, and 12 wt.% divinylbenzene (technical grade) [300–550K]. Polystyrene and poly(α‐methylstyrene) data were found to match the ATHAS data bank collections. Crosslinking causes no significant change in heat capacity, but substitution does. The heat capacities in the solid state are evaluated using approximate group and skeletal vibration spectra. Glass transitions are discussed, and full thermodynamic functions (Cp,H,S,G) can be calculated for amorphous, crystalline, and deuterated polystyrene as well as poly(α‐methylstyrene). Glassy polystyrene has an entropy of 7.5 J K−1mol−1at absolute zero. Changes of the heat capacity at the glass transition are explained and are predicted to go to zero for 50% poly(styre

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241209

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractPolystyrene‐co‐4‐hydroxystyrene ionomers (3.0–22 mol%) were synthesized via neutralization of demethylated polystyrene‐co‐4‐methoxystyrene. The physical properties of the ionomers as well as their nonionic precursors were studied by calorimetry, torsion pendulum and small‐angle X‐ray scattering (SAXS). Evidence for ion aggregation was obtained for the styrene‐4‐hydroxystyrene ionomers from SAXS and tor

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241210

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY