摘要:

AbstractThe effects of drawing temperature on the physical and mechanical properties of poly(p‐phenylene sulfide) have been studied. A melt‐quenched film was drawn by solid‐state coextrusion both below (75°C) and above (95 and 110°C) the glass transition temperatureTg(85°C) of PPS. The maximum extrusion draw ratio (EDRmax) increased from 3.4 to 5.6 with increasing extrusion temperatureTefrom 75 to 110°C. It was found that extrusion drawing just above theTgof PPS (95°C) produced more stress‐induced crystals. A high efficiency of draw in the amorphous region was achieved by extrusion at Te‐75°C. The tensile modulus at EDRmaxdecreased from 5.1 to 3.5 GPa with increasingTefrom 75 to 110°C. The low efficiency of draw for the samples extruded at 110°C is explained in terms of disentanglement and chain slippage during drawing due to a less

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230201

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThermotropic polymers and low‐molecular‐weight mesogens share many common textural features. This circumstance is exploited to determine diffusion coefficents in a system consisting of a cholesteric polymer and a low‐molecular‐weight nematogen using the recently developed optical mass transport method. The self‐diffusion coefficient and its concentration dependence were determined by using a distance–time approach, whereas the time dependence of the mutual diffusion coefficient was evaluated by a conventional concentration–distance analysis of the diffusion profile. Comparison with literature data indicates satisfactory agreement. The coefficient of the scaling law relating the self‐diffusion coefficient and concentration is in accord with the value predicted by de Gennes for semidilute po

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230202

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractA unique crystal structure of the α‐helical form of poly(γ‐methylL‐glutamate) appearing above 170°C is analyzed by x‐ray diffraction. At room temperature, the unit cell determined for a well‐annealed sample is hexagonal with dimensiona= 11.82Å and contains one α helix with pitchP= 5.42 Å and unit heightp= 1.493 Å. This form is reversibly transformed at about 170°C into a modification characterized by a trigonal unit cell (a= 21.27Å) having three times the cross section of the single‐chain unit cell and containing three α helices withP= 5.50 Å andp= 1.504 Å. In a narrow temperature range below 180°C, the three chains in the unit cell are not interrelated by any crystallographic symmetry element, but they are reasonably associated with one another so that all helices are surrounded by other helices in the same way. The axial and azimuthal displacements between neighboring chains are expressed byz= ±4p/3 and ϕ = ± (2π/3)(4p/P− 1), respectively. The segmental main‐chain motion, which becomes appreciable above 150°C, is composed of screw‐type motion along the α‐helix fold and correlatedP/3 axial jumps. The relation between the structural tran

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230203

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractConceptual differences in two recent versions of the free‐volume theory for self‐diffusion in polymer–solvent systems are identified and discussed. The validity of the assumptions of these two theories is tested using experimental data. In all cases, the experimental evidence favors the Vrentas–Duda free‐volume theory over the Paul version of th

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230204

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe predictive and correlative capabilities of two recent versions of the free‐volume theory for self‐diffusion in polymer–solvent systems are examined by comparisons with experimental data. Neither the Vrentas–Duda free‐volume theory nor the Paul version generally provides satisfactory predictions for the temperature and concentration variations of solvent self‐diffusion coefficients. However, the Vrentas–Duda theory does provide good correlations of solvent self‐diffusion data, and, furthermore, this theory can provide good predictions if a small amount of solvent self‐diffusion data is used to help estimate the parameters of the theory. New diffusivity and equilibrium data were collected for the toluene‐PVAc system to provide a broader database for evaluation of the self

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230205

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe morphology of fully and partially polymerized poly(phthalocyaninatogermoxane), [Ge(Pc)O]n, crystals was studied by both scanning and transmission electron microscopy. It was found that the morphological units are lath‐like crystals which aggregate into particles. Generally speaking, the thickness, width, and length of the laths are in the range of 1000–2000 Å, 2000–10,000 Å, and 1–5 μm, respectively. Each lath may possess a mosaic substructure. Selected‐area electron diffraction patterns indicate that the rigid, extended [Ge(Pc)O]nchains are parallel to the large surface of the lath, and in most crystals the chains lie parallel to the lengthwise direction of the lath. However, in several cases, the chain orientation is at an angle of about 60° with respect to the long edge of the lath. The electron diffraction results are in accord with a tetragonal crystal str

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230206

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe second and fourth moments of the proton resonance line in stretched poly(vinyl alcohol) samples have been measured by a pulse technique. Their anisotropy has been analyzed at different elongation ratios λ. The use of the second and fourth moments gives an interesting cross‐check on the reliability of the results. Despite the fact that the lattice sums required for absolute determination of the orientation cannot be calculated, coefficients related to the second and fourth moments of the orientation distribution function can be compared to the prediction of the quasiaffine orientation scheme for the crystalline phase and to the experimental values of the birefringence as a function of λ. It is shown that NMR clearly detects the onset of the orientation of the amorphous chains above λ

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230207

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractPhase equilibria of polydisperse rods in solution are studied in terms of the Warner–Flory model. Numerical calculations are made with a Gaussian‐like asymmetric distribution of rod lengths. The aim of these studies is to investigate (i) the dependence of the phase diagram on the shape of the polydispersity distribution function and (ii) the isotropic–anisotropic phase separation within the coexistence range. It is shown that, as a consequence of polydispersity, even for a narrow distribution, the phase diagram is very simple, with only one type of anisotropic phase present. However, within the biphasic range, the properties of the anisotropic phase vary significantly with temperature. At high temperatures, they are essentially governed by steric effects and at low temperatures by both steric effects and soft anisotropic interactions between the

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230208

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe chemical modifications induced in diphenyl carbonate (DPC) by sodium arylcarboxylates between 200 and 250°C were studied to model the behavior of bisphenol‐A polycarbonate – salt systems. Reaction between the salt and DPC produces sodium phenoxide, the phenyl arylcarboxylate corresponding to the salt, and carbon dioxide. The two latter compounds probably result from the decarboxylation of an unstable intermediate compound, viz., a mixed carboxylic carbonic anhydride. CO2and sodium phenoxide act as catalysts transforming DPC into phenyl salicylate via the formation of a small amount of sodium salicylate. Electrophilic acylation of sodium phenoxide by DPC is another possible but minor source of phenyl salicylate. Above 250°C, phenyl salicylate becomes unstable and pyrolyzes intoo‐phenoxybenzoic acid, which is immedicately esterified in the presence of DPC into phenylo‐phenoxybenzoate. In DPC + sodiumo‐chlorobenzoate systems, reaction between phenylo‐chlorobenzoate and sodium phenoxide is another source of phenylo‐

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230209

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractIn the presence of sodiumo‐chlorobenzoate, bisphenol‐A diphenylcarbonate (BADPC) undergoes complex chemical modifications from 170°C. Reaction between BADPC and minute amounts of salt produces sodium phenoxide end groups which undergo a fast exchange reaction with the carbonate groups of BADPC. In a closed system, an equilibrium molecular weight distribution is progressively attained which agrees fairly well with the one predicted from a simple model based on Bernoulli statistics. In an open system, the equilibrium is continuously displaced by the evaporation of volatile diphenyl carbonate. This leads to a steady increase of the molecular we

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230210

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY