摘要:

AbstractThe relaxation spectrum of poly(dicyclohexyl itaconate) (PDCHI) was studied by dynamic mechanical, DC dielectric and thermally stimulated current measurements. Four relaxations, α, β, γ and δ, were obtained. The only method by which all four peaks were observed is that of dynamic dielectric measurements because of the broad range of frequencies employed. The β, γ and δ relaxations were characterized by the activation energy in a relaxation map. A tentative explanation of the molecular origin of each absorption is proposed. In the case of the α relaxation we have used two transformations, one from the permittivity to polarizability and the second from compliance to deformability in order to make evident the existence of this rel

ISSN:0959-8103    

DOI:10.1002/pi.4990290302

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe permeability of native and commercial grades of gutta‐percha (trans‐polyisoprene), was determined and related to diffusion rate both below and above the glass transition temperature (Tg) and the melting point (Tm). Both radially drawn and undrawn membranes were evaluated. Five gases (O2, N2, CO2, H2and He) were used as permeants and the measurements were taken both above and below the polymers' crystallineTm. The diffusivity of the gases was found to have an increased rate above theTm. The reduction of solubility, diffusivity and permeability with increasing draw ratio was attributed to an increase in crystallin

ISSN:0959-8103    

DOI:10.1002/pi.4990290303

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe miscibility of blends of poly (ε‐caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL‐rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameterx12, was calculated from the Nishi‐Wang equation and the value was found to be‐1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice‐fl

ISSN:0959-8103    

DOI:10.1002/pi.4990290304

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPalladium complexes of cross‐linked polyvinylpyridine and poly(acryl‐amide‐methacrylic acid) copolymer coated on silica gel have been used as catalysts for the hydrogenation of azo and nitro groups under 101 kPa hydrogen pressure at 30°C. Nitro aromatics were selectively and almost completely reduced to the corresponding amines. A rate equation of the type, rate =k[cat][H2] has been derived for the hydrogenation of nitrobenzene on the basis of the experimental results and kinetic data. Also the selective hydrogenation of azobenzene to hydrazobenzene could be achieved with these cat

ISSN:0959-8103    

DOI:10.1002/pi.4990290305

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe diglycidyl ether of bisphenol‐A (DGEBPA) was modified by acrylic acid. The reaction between the active epoxy groups of DGEBPA and the carboxylic group of acrylic acid was catalysed by triphenyl phosphine to prepare di(vinyl‐2‐hydroxypropanoate) ether of bisphenol‐A (DEBA). The DEBA so formed was co‐polymerised with 2‐ethylhexylacrylate using benzophenone as the photo‐initiator to yield a flexible polymer. The kinetics of the photo‐initiated radical polymerisation was studied by a new technique called differential photo‐calorimetery and the results thus obtained were analysed to determine the Arrhenius activation energy and pre

ISSN:0959-8103    

DOI:10.1002/pi.4990290306

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractSize exclusion chromatography (SEC) has been used to study the influence of molecular weight on the reactivity of the hydroxyl group in free radically polymerised hydroxyl‐terminated polybutadiene (HTPB). The HTPB prepolymer was converted into a UV‐absorbing urethane derivative by reaction with phenylisocyanate and the degree of conversion was followed from the UV/DRI (Differential Refractive Index) signal of the derivative using dual detector SEC. Though the overall reaction levelled off at about 70% conversion at room temperature, the time taken by different molecular weight species to attain this level was different. The computed rate constants were larger for the higher molecular weights in a given sample. This is attributed to the polyfunctionality of the higher molecular weight spec

ISSN:0959-8103    

DOI:10.1002/pi.4990290307

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction between 1,5‐diethenylnaphthalene andsec‐butyllithium produces a new difunctional organolithium initiator which is soluble in non‐polar solvents and effective in the synthesis of styrene‐isoprene‐styrene triblock copolymer. Monomodal molecular weight distributions are observed for block copolymers and styrene homopolymers. The microstructure of polyisoprene blocks is similar to those polymers initiated by butyllithium in the sam

ISSN:0959-8103    

DOI:10.1002/pi.4990290308

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA new semicrystalline polyimide has been synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane. The polymer has a high glass transition temperature of 230°C and a melting temperature of 325°C. Its overall crystallization rate between 240 and 325°C is quite fast (t1/2<10min) and relatively insensitive to the crystallization temperature. Although the degree of crystallinity obtained is dependent on the crystallization conditions, it can be as high as 50%. The polymer's morphology, which was examined with transmission electron microscopy (TEM), has a randomly stacked, ribbon‐like, lamellar texture. Both TEM and polarized light microscopy show that mature spherulites do not develop. The crystal unit cell, which was determined from wide‐angle X‐ray diffraction measurements on highly oriented films, is monoclinic witha= 0.960nm,b= 0.582nm,c

ISSN:0959-8103    

DOI:10.1002/pi.4990290309

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPolymerization of 1,3‐butadiene was conducted with a CoBr2(PPh3)2and methylaluminoxane catalyst. From the spectroscopic analysis of both crude and hydrogenated polymers, it was found that the polymer produced with the catalyst was composed of approximately 35%cis‐1,4‐ and 65% 1,2‐units without stereoregularity. Effects of temperature, Al/Co ratio and addition of some Lewis bases on the polymerization were also examined in some

ISSN:0959-8103    

DOI:10.1002/pi.4990290310

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of iron doping and its concentration on the dielectric properties of cellulose acetate films was studied as a function of temperature (range 300–440 K) and frequency (range 10 kHz‐10 MHz). Undoped films exhibited a peak near 350 K in the capacitance versus temperature plots, while the dielectric loss exhibited two peaks. The dielectric capacitance decreased with increased dopant concentrations while the dielectric loss showed an increase. The peak positions, however, shifted towards higher temperatures in both cases. Presence of dopant ions and formation of charge transfer complexes/molecular aggregates are suggested as the possible reasons for this behavi

ISSN:0959-8103    

DOI:10.1002/pi.4990290311

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY