摘要:

AbstractFine threads ofcis‐1, 4‐polyisoprene, diameter ca. 50μm, were prepared by drawing from solution and drying. They were crosslinked by reaction with H2S and SO2and then swollen with linearcis‐polyisoprene liquids of varied molecular weightMs, from 1,000 to 24,000 g/mol. Diffusion coefficients were determined from the initial rate of uptake, for both unrestrained and stretched threads. They were found to be in good agreement for stretches of up to about 300%. On the other hand, the equilibrium uptake increased markedly (>100%) over this range of strain, similar to the increase in swelling observed with low‐molecular‐weight liquids. Values of diffusion coefficient were also obtained from the rate of deswelling upon release of swollen threads from tension, and from the rate of uptake of polymer liquids by a thin coating of crosslinked polymer, bonded onto glass fibers. Satisfactory agreement was obtained in all cases. A number of simple experiments thus give similar values for the diffusion coefficient of polymer liquids in lightly crosslinked polymer networks, in the range 10−13−10−16m2/s, depending upon the molecular weightMsof the polymer liquid approximately weight asM−2s. The amount of liquid absorbed was strongly dependent on its molecular weight,Ms, the degree of crosslinking of the host material, and applied stres

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291101

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe polarized reflection spectrum was used to evaluate the surface orientation of extruded sheets of liquid‐crystalline copolyester consisting of 73 mol % 4‐hydroxybenzoic acid units and 27 mol % 2‐hydroxy‐6‐naphthoic acid units. The anisotropy of absorption index was evaluated from the specular reflectance using the Fresnel equation and the Kramers‐Kronig relation. An intense absorption and observed in the ultraviolet region was assigned to the π*←π transitions of the constituent monomeric units. The observed spectra of the liquidcrystalline polymer were successfully interpreted by use of the spectroscopic data on the monomers. The transition moment directions of the monomeric units were calculated by molecular orbital calculations within the framework of the CNDO/S‐Cl approximation. The Surface orientation functions obtained from polarized reflection spectra were compared with the crystal orientation functions in the bulk, which were obtained from the azimuthal intensity distribution of wide‐angle x‐ray diffraction. The orientation behaviour at the surface of the liquid‐crystalline polymer was shown to be equivalent to the orientation behaviour in the bulk at

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291102

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA new model for the dynamic relaxations occurring below the glass transition temperature in amorphous polymers is introduced. This model combines ideas from theoretical solidstate physics, thermodynamics, and statistical mechanics. Formal analogies are made between the dynamic relaxations and phase transitions. The concepts of percolation theory are briefly discussed. The molecular level motions which might be giving rise to each dynamic relaxation are incorporated within this framework. The simplest version of the model is then formally implemented within the context of bisphenol‐A polycarbonate (BPAPC) and its poly (ester carbonates) (PEC). The following results are calculated: (1) Characteristic temperatures (Tc) for BPAPC, similar toγ1, andγ2relaxation temperatures observed by dynamic mechanical spectroscopy (DMS) at commonly used measurement frequencies. (2)Tcfor theβ2relaxation in tetrabromo‐BPAPC much higher than theTcin BPAPC. (3) A slow and monotonic increase in both the intensity and theTcof theγ2relaxation with an increasing fraction of terephthalate comonomer in PEC copolymers. It is hoped that this model, which is admittedly tentative at this time, will be useful as a working hypothesis. The next paper of this series will provide extensions and generalizations of the model, and its application to the poly (alkyl methacr

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291103

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractExtensions and generalizations of a new model for the dynamic relaxations in amorphous polymers, and its application to the poly(methacrylates), will be presented. The sizes of moving subunits will be extrapolated for the β and γ relaxations in several poly(methacrylates), by working backward from the relaxation temperatures (Tr) observed at frequencies of 1 to 100 Hz to subunits givingTcs comparable to thoseTrs. A general form will be proposed for activation energy distributions; and used to derive relaxation time distributions satisfying the experimental trends. The good agreement between the calculatedTcand theTrobserved dynamically at frequencies of 1 to 100 Hz will be shown to result from the nature of these distributions. The loss peak observed at very low temperatures by isochronal sweeps at very low frequencies is therefore caused by the dissipation of applied energy in localized domains. At sweep frequencies of 1 to 100 Hz,Tr≈Tc, and energy dissipation begins to take place over regions spanning the entire polymer. This delocalization of the energy dissipation is relevant to the effects of molecular level factors on many mechanical and thermodynamic properties of amorphous polymers. The effects of activation entropy and of dynamic excess entropy will be shown to be small in magnitude but important in terms of fully understanding relaxation behavior. Physical aging will be shown to result in a slight increase in the calculated characteristic temperatures. Finally, it will be shown that the relaxation behavior of the moduli and the compliances share some important common features with many other physical phenomena of seemingly very different nat

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291104

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe nonaqueous solution behavior of random copolymers of styrene (ST) with sodium‐2‐acrylamido‐2‐methylpropane sulfonate (Na‐AMPS) [poly(ST‐Na‐AMPS)] has been investigated using the transient electric birefringence (TEB) technique. The copolymers with varying high sulfonate contents (about 30–70 mol%), bridging the gap between conventional ionomers and classical polyelectrolytes, were dissolved in the solvent methylformamide (MFA) with a high permittivity ϵ of ca. 190. The solutions showed a negative birefringence at electric field strengthEof the order of kV/cm. A typical Kerr effect was observed at low polymer concentrationsCof ca. 10−3g/mL and electric field strengths of the order of kV/cm. However, the detailed, TEB studies demonstrated different behavior at two concentration regimes in dilute solution. At a low concentration regime (e.g.,C≤ 1 × 10−3g/mL for the copolymer with a 66.7 mol % sulfonate content) where the reduced viscosity exhibited a pronounced polyelectrolyte effect, the birefringence signal pattern showed a maximum before reaching a steady value. Additionally, during the rise at an applied electric field strength beyond a threshold value, it was observed that the nonexponential field‐free decay was slower than the single exponential field‐induced rise. The observed anomalous behavior was similar to those of a polyelectrolyte [sodium poly (styrene sulfonate)] in aqueous solution and might be attributed to the perturbation of the molecular shape by the applied electric field. At the higher concentration regime (e.g.,C≥ 4 × 10−3g/mL for the same copolymer with a 66.7 mol % sulfonate content) where the polyelectrolyte effects started to diminish as indicated by the viscosity study, the birefringence shape showed no variation with an increased electric field strength and the field‐free decay turned out to be faster than the single exponential rise. The dissociation of ionic aggregates was tentatively interpreted to be responsible for this observation. It seems that by simply varying the polymer concentration, poly (ST‐Na‐AMPS) could behave either as a polyelectrolyte or as an ion

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291105

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe cholesteric mesophase of the PBLG‐BA system in concentrated solutions and in the gel phase has been investigated by static laser light scattering. The observed ‘distortion’ of the patterns in terms of their dependence on the azimuthal angle was studied. Effect of form‐optical rotation on the pattern is discussed. The manner of distortion in theHvpattern determines the sense of cholesteric twisting. The observed scattering patterns are analogous to those obtained by previous investigators in other solvents. Quantitative measurements of the intensity as a function of scattering vector provide information on the sense and pitch of the cholesteric twisting, as a function of temperature and concentration. Optical microscopy studies reveal onset and build‐up of the cholesteric structure. Optical rotation and differential scanning calorimetry (DSC) studies support the conclusions obtained from light‐scattering

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291106

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractLocal ordering in miscible binary polymer blends with strong attractive interactions between the two types of chains was investigated by computer simulation of allowable conformations on an incompressible cubic lattice. A tendency toward maximum ordering (in which chains pack in alternate parallel rows) is shown by the calculation of pair correlations and in “snapshots” of the mixtures. A specific directional interaction is not necessarily required for ordering. A comparison of these results with those recently obtained using mean‐field theory is presented. The heat capacity of mixing was also calculated and found to be positive, with a value close to that reported experimen

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291107

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractStudies utilizing absorption and emission spectrophotometry have been carried out to observe the effect of various polymer substrates on the spectral characteristics of several stilbene‐based fluorescent dyes. Poly(vinyl alcohol), cellulose acetate, cellulose fiber, and bovine serum albumin were used as substrates for two common fluorescent whitening agents and for two model compounds. Binding of these molecules to polymers leads to a marked red shift in the absorption spectra and an increase in vibrational structure. These effects are attributed to an increase in molecular planarity induced by the polymer environment. For the case of bovine serum albumin, it is concluded that the dye molecules bind to the protein largely through electrostatic interaction involving the dye sulfonate groups. The spectral characteristics of the dye molecules on wool fibers are interpreted in light of these result

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291108

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThermal analysis and wide‐angle x‐ray diffraction were used to assess the crystallinity for a series of poly(vinyl chloride) (PVC) samples, and the use of two complementary techniques was found beneficial. Two polymers were studied; a commercial suspension grade PVC, and an experimental grade of higher syndiotacticity. Both were examined as powders, and after processing. All samples were also examined after heat treatment at various temperatures between 100 and 175°C. Annealing the suspension grade of PVC appeared to cause a small change in total crystallinity, but little change in crystallite size. When the low temperature powder was annealed, some increase in crystallinity was detected. However, when this polymer was milled, there was a significant increase in crystallite size, and crystallinity seemed to increase further. Particularly noticeable was the increase in the amount of high melting crystall

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291109

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractTime‐resolved light scattering was employed to investigate kinetics of phase separation in mixtures of poly (ethylene glycol monomethylether) (PEGE)/poly (propylene glycol) (PPG) oligomers. Phase diagrams for PEGE/PPG of varying molecular weights were established by means of cold point measurements. The oligomer mixtures reveal an upper critical solution temperature (UCST). Several temperature quench experiments were carried out with a 60/40 PEGE/PPG blend by rapidly quenching from a single phase (69°C) to two‐phase temperatures (66–61°C) at 1°C intervals. As is typical for oligomer mixtures, the early stage of spinodal decomposition (SD) was not detected. The kinetics of phase decomposition was found to be dominated by the late stage of SD. Time‐evolution of scattering intensity was analyzed in accordance with nonlinear and dynamical scaling theories. The time dependence of the peak intensityImand the corresponding peak wavenumberqmwas found to follow the power‐law {Im(t)˜tα,qm(t)˜t‐β} with the values of α = 3 ± 0.3 and β = 1 ± 0.2, which are very close to the values predicted by Siggia. This process has been attributed to a coarsening mechanism driven by surface tension. In the temporal scaling analysis, the structure function reveals university with time, suggesting self‐similarity. Phase separation dynamics in 60/40 PEGE/PPG resembles the behavior predicted f

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291110

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY