摘要:

AbstractWe present a detailed criticism of the kinetic approach to the analysis of data obtained from measurements of the very weak chemiluminescence accompanying the oxidation of polypropylene. It is shown that a kinetic model proposed by other workers is based upon invalid assumptions, leads to kinetic parameters which are not sensible, and requires measurement of the properties which it claims to predict.

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280301

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractWide‐angle x‐ray diffraction experiments on Kevlar 49 fibers, irradiated with γ‐rays from a Co60source, indicated that radiation‐induced cross‐linking in the form of H‐bonding occurred within the microparacrystals (mPC) in the lateral directionbof the unit cell and had led to an increase in the mPC size in this direction. On the other hand, the mPC sizeI200along the axis and normal to the [200] netplanes did not change by radiation. In effect, the mPC size normal to the [110]netplanes increased from 4.23 nm to a maximum value of 6.04 nm at the 600 MRad dose level, after which it decreased. The mPC size in the direction of the fiber axis was 102 nm and did not change significantly by radiation (102–109 nm). Thus, essentially, the mPCs grew solely in thebdirection. The paracrystalline distortion parameter (g) in the direction of the fiber axis was 2.8% and was not changed significantly by radiation (g= 2.9 ± 0.2%). The equatorial “crystallinity” maintained a value of 76% until a dose of 50 MRad and then became 73% at 100 MRad and 70% after this dose level The netplane distances were not af

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280302

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe γ‐radiolysis behavior of poly(l‐chloro‐1‐alkynes)\[ [\rlap{‐‐} ({\rm CCI} = {\rm CR}\rlap{‐‐} )_n ;{\rm R} = n ‐ {\rm alkyl}]\]greatly changed with the length of alkyl group and with the presence or absence of oxygen. When γ‐irradiated in air, poly(l‐chloro‐1‐hexyne) (R =n‐C4H9) decomposed to oligomers; itsGsvalue was as large as 5.4. When irradiated in vacuum, this polymer partly gelled. In contrast, poly(l‐chloro‐1‐decyne) (R =n‐C8H17) partly gelled even by irradiation in air. A high‐dose irradiation of this polymer in vacuum resulted in the quantitative formation of a gel. The polymers irradiated in air contained carbonyl and hydroxyl groups, indicating the participation of oxidation reaction. Comparison with their thermolysis leads to a conclusion that these Cl‐containing polyacetylenes are radiation‐sensitive i

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280303

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractIt has been shown that incorporation of masked isocyanates in the MY720/DDS epoxy significantly reduces the equilibrium moisture absorption by blocking of residual functional groups ( oxirane group) by the isocyanates released in the deblocking reaction of the masked isocyanates. We have now used high resolution13C‐CP/MAS NMR to follow the reactions in the solid state and to identify intermediates and by‐products. The deblocking reaction of the masked isocyanates also releases the corresponding alcohol, part of which may evaporate during the curing reaction. The resolution in the solid‐state spectra is good enough to identify all the reactants and the intermediates involved in the curing reaction. Difference spectra are used to emphasize changes between systems that differ in treatment or compos

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280304

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractCationically charged poly(allylamine) (PAA) membranes having various water contents [0.49

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280305

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe viscoelastic behavior, order‐disorder transition, and phase equilibria in mixtures of a block copolymer and an endblock‐associating resin were investigated. The block copolymer was a polystyrene‐block‐polyisoprene‐block‐polystyrene (KRATON® D‐1107, Shell Development Co.) copolymer. The endblock‐associating resins investigated were two different grades of a commercially available random copolymer of poly(α‐methyl styrene) and polystyrene, one with a weight‐average molecular weight \[\bar M_{\rm w}\] of 710 (KRISTALEX® 3085, Hercules Inc.) and the other with \[\bar M_{\rm w}\]= 4100 (KRISTALEX® 5140, Hercules Inc.). Mixtures of various proportions of the block copolymer and the endblock‐associating resin were prepared in toluene solvent. With the mixtures, measurements of dynamic viscoelastic properties were made, namely, dynamic storage modulus G″ and dynamic loss modulus G″ as a function of temperature from temperature scans of the samples using a Rheometrics Mechanical Spectrometer. The following observations were made. (1) The plateau modulus of the block copolymer increased with increasing amount of KRISTALEX 3085 or KRISTALEX 5140, indicating that the low‐molecular‐weight resin was associated with the polystyrene microdomains of the block copolymer. (2) When KRISTALEX 3085 (up to 30 wt %) was added to the block copolymer, the glass transition temperature (Tg) of the polyisoprene midblock of the SIS block copolymer was shifted toward higher temperatures, indicating that part of the KRISTALEX 3085 added had associated with the rubbery midblock of the block copolymer. Also investigated was the order‐disorder transition behavior of the mixtures, using a rheological technique (logG′ versus logG″ plots) recently introduced by Han and Kim. It has been found that the order‐disorder transition temperatureTrof mixtures of the SIS block copolymer and KRISTALEX 3085 decreased steadily with increasing amount of KRISTALEX 3085, whereas the addition of KRISTALEX 5140 increased theTrof the block copolymer. It was found by light scattering and hot‐stage microscopy thatmacrophaseseparation occurred in the KRATON 1107/KRISTALEX 5140 mixtures whilemicrodomainsof poly

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280306

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractDirect determination of the Flory‐Huggins interaction parameter χ of a polymer blend by small‐angle x‐ray scattering experiments is possible on the basis of the random phase approximation, if absolute intensities are measured. The usually superposed void scattering has to be properly accounted for. Investigations on a series of blends of polystyrene and poly(styrene‐co‐bromostyrene) yielded χ dependent upon the blend composition. χ shows only slight variations. Scattering data also give the radii of gyration of the two components

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280307

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe miscibility of poly(viny1 alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) blends is investigated by differential scanning calorimetry (DSC) and wide‐angle x‐ray diffraction (WAXD). The molecular orientation induced by uniaxial stretching of the blends is also examined by WAXD and birefringence measurements. It is shown by the DSC thermal analysis that the polymer pair is miscible, since a single glass transition temperature (Tg) is situated between theTgs of the two homopolymers at every composition. TheTgversus composition curve does not follow a monotonic function but exhibits a cusp point at a PVP volume fraction of a little under 0.7, as in a case predicted by Kovacs' theory. The presence of a specific intermolecular interaction between the two polymers is suggested by an observed systematic depression in the melting point of the PVA component. A negative value of the polymer‐polymer interaction parameter, χ12= 0.35 (at 513 K), is estimated from a thermodynamic approach via a control experiment using samples crystallized isothermally at various temperatures. The extent of optical birefringence (Δn) of the drawn blends decreases drastically with increasing PVP content up to 80 wt %, when compared at a given draw ratio, and ultimately Δnis found to change from positive to negative at a critical PVP concentration of a little over 80 wt %. Discussion of the molecular orientation behavior takes into consideration a birefringence compensation effect in the miscible amorphous phase due to positive and negative contributions of oriented PVA and PVP, resp

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280308

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractPoly(1‐trimethylsilyl‐1‐propyne)/poly(dimethylsiloxane) (PTMSP/PDMS) graft copolymer was prepared to evaluate the permeation characteristic at pervaporation of aqueous ethanol solution through the graft copolymer membrane. For the preparation of PTMSP/PDMS graft copolymer, an improved synthetic procedure was released in this paper, which comprised a one‐pot reaction of PTMSP in lithium bis(trimethylsilyl)amide followed by treatment with hexamethylcyclotrisiloxane and trimethylchlorosilane. PDMS content of the graft copolymer was controlled in the range 5–74 mol%. Very tough and thin membranes could be prepared from these copolymers having various PDMS content by the solvent casting method. The permselectivity of the membranes was investigated by pervaporation of ethanol/water mixture at 30°C. Preferential permeation of ethanol was observed for the membranes. It was also found that the selectivity of every copolymer membrane was higher than that of the PTMSP membrane. Moreover, the selectivity depended on the PDMS content of the graft copolymer. The separation factor and permeation rate assumed the maximum values at 12 mol% PDMS content. At the maximum point, 7 wt% aqueous ethanol solution was concentrated to about 70 wt% ethanol solution, and the separation factor and permeation rate were 28.3 and 2.45 × 10−3g · m/m2· h, respectively. Such a high permselectivity for ethanol might be due to a delicate alteration of membrane structure, which was induced by the introduction of a short PDMS side chain into a

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280309

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of physical aging below the glass transition temperature on selected properties of polycarbonate have been studied. Changes in tensile yield strength, post yield stress drop, and fracture toughness as a result of annealing at 120°C for 240 h have been measured and are related to changes in free volume as measured by positron annihilation lifetime spectroscopy. The free volume concentration remains constant during the aging heat treatment at 120°C but decreases after cooling due to aging. The relationship between free volume changes and physical property changes is discussed in terms of molecular conformations and fracture mode. The effect of aging on fracture morphology is presented to aid interpretations of fracture mod

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280310

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY