摘要:

AbstractMethods to synthesise soluble poly(2‐hydroxyethyl methacrylate) (PHEMA) with varying molar mass were developed. Conversions over 90% were achieved without losing solubility. Steady state tests (range 0.01–590 Pa) and oscillatory tests (range 0.001–40 Hz) were carried out on 40% solutions in dimethyl formamide using a Carri‐Med rheometer. Only PHEMA having molar mass over 500000 showed significant shear thinning and viscoelastic properties. The copolymers of 2‐hydroxyethyl methacrylate (HEMA) withn‐butyl acrylate (BA) and 2‐hydroxypropyl acrylate (HPA) showed higher viscosities and viscoelastic properties compared with PHEMA homopolymer prepared under identical conditions. Also, viscosity and viscoelasticity increased with increase in acrylate content in the initial mixture. This was attributed to the higher molar mass of copolymers, which resulted from faster polymerisation rates owing to the inclusion of relatively highly reactive acrylates. However, in the case of HEMA : BA copolymers, first, the viscosity and viscoelasticity increased with increasing BA content and then dropped again, giving a maximum around HEMA : BA 75 : 25. This anomaly was explained by taking the effects of changes in inter‐and intra‐molecular hydrogen bonding as well as conformational differences caused by inclusion of BA in the PHEMA c

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360401

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractDifferent grades of impact‐modified polystyrene were studied by viscometry, tensile impact test and colour change upon exposure to polychromatic irradiation at 55°C in air. The samples underwent extensive reduction in intrinsic viscosity [η] and tensile impact strength, and yellowed upon polychromatic irradiation (λ ≥ 290 nm). Chain‐scission during photo‐oxidative degradation was also studied under conditions where evolution of volatiles was negligible. Tristimulus values were calculated for unirradiated and irradiated samples. The rate of oxidative degradation was maximum in the sample possessing higher unsaturati

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360402

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA systematic dielectric study was carried out over a frequency range 60 Hz–300 kHz and at temperatures between 5 and 90°C on dehydrated castor oil mixed with different concentrations of styrene monomer to produce an insulating varnish. The volume resistivity was also studied. The results show that, when dehydrated castor oil is mixed with 10% styrene content by weight of the oil, epoxidised and then chemically treated with melamine resin and other additives, a varnish is produced with favourable electrical insulation properti

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360403

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSolutions of polystyrene‐block‐poly(ethylene/propylene) and polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene copolymers in 5‐methyl‐2‐hexanone and 4‐methyl‐2‐pentanone were studied by size exclusion chromatography. The association equilibrium was studied shifting from micelles to free copolymer chains by increasing the temperature. A remarkable tailing was observed in diblock copolymer micelle peaks that may be explained by the disturbance and restablishment of the association equilibrium during separation in the chromatographic column. This phenomenon was very small for triblock copolymers. In this case, micelle hydrodynamic volumes obtained from SEC curves were compared to those calculated from light scattering and viscosity measurements. The data agreement was very good. Comicellization was analysed by mixing two different micelle solutions and injecting the solution mixture at different elapsed times. The SEC curves showed an intermediate peak corresponding to mixed micelles. The results show that three micelle species coexist in solution during the first period after mixing, which suggests that comicellization proceeds via dissociation of pure micelles and association of both copolymer free chains to form

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360404

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

Abstracto‐Cresol‐formaldehyde resin (OC) and five kinds of acetylated OC (AC‐X‐OC;Xis the degree of acetylation) were prepared. The Θ‐temperature for each resin was determined by means of the Shultz‐Flory method, and their molecular conformations in both tetrahydrofuran (THF) and Θ‐solvent were estimated from the values of the exponents in the Mark–Houwink–Sakurada equations. The effect of the degree of acetylation on the exponent was negligible in THF, but was remarkable in Θ‐solvent. In THF, the molecular chains of these resins are relatively extended, because the hydrogen bond between phenolic hydroxyl groups is loosely formed. In Θ‐solvent, however, the molecular conformation is compact and the resins are considered to form a pseudo cross‐linked network structure through inter‐ and/or intra‐molecular hydrogen bonds. The Mark–Houwink–Sakurada equation for AC‐100‐OC in 2‐ethoxyethanol at 92.0°C was found to be [η]θ= 0.0773 M̄0.50n, where [η]0is the limiting viscosity number under the Θ‐condition, and M̄nis the number‐average molecular weight. The unperturbed dimension, (〈r20〉/M̄n)1/2, 〈r20〉 being the unperturbed mean square end‐to‐end

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360405

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe crystalline–amorphous polymer pair of poly(vinylidene fluoride) and poly(methyl methacrylate) is known to be miscible over a wide composition range. The effects of ionic moieties on the miscibility were studied by replacing the poly(methyl methacrylate) with a series of random copolymers of methyl methacrylate and potassium salt of methacrylic acid. The interaction parameter (χ) for the miscible blends in their molten state was obtained by thermal analysis using a melting‐point depression calculation. The parameter decreased to a minimum atc.2% ion content (χ=minus;0.514) and approached a positive value at above 10% ion concentr

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360406

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe poly(N‐vinyl‐2‐pyrrolidone)(PVP)(2)/water(1)/CdCl2(3) ternary system has been studied by viscometry, densimetry and atomic absorption spectrophotometry. In this system a preferential adsorption of Cd2+at all solvent compositions studied and a conformational transition at 4mMof salt, the concentration at which a preferential adsorption minimum of Cd2+in exhibited, are observed. The PVP/Cd2+bound molar ratio is 0·23. CdCl2behaves as a salting‐in agent for the macromolecule. The binary solvent mixture is thermodynamically more favourable at salt concentrations greater than 10 mM

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360407

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSorption and diffusion ofn‐alkanes into bromobutyl rubber membranes were investigated in the temperature interval 25–60°C by a sorption gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes, their interactions with the chain segments of the polymer and temperature. The diffusion coefficients varied from 0.34×10−7cm2/s (n‐hexadecane) to 9.94×10−7cm2/s (n‐hexane). The activation energy for diffusion varied from 14kJ/mol (n‐hexane) heptane to 2.0kJ/mol forn‐hexadecane. The sorption/swelling results are discussed in terms of first and second order kinetic equations. The molar mass between chain‐entanglement‐crosslinks was estimated from swelling data. The experimental and calculated results showed a systematic dependence on the increasing size of the alkanes. None of the solvents showed any degradative

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360408

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractInduction and stabilization of free radicals were investigated in hematoporphyrin‐IX (Hp)‐doped chitosan (Hp‐Ch) film by electron spin resonance (ESR) following photo‐irradiation. Induced radicals were more stable in chitosan and 6‐O‐carboxymethyl chitin films than in carboxymethyl cellulose and sodium alginate films. Hydroxyl groups on D‐glucosamine residues in chitosan are suggested as participating in accepting radicals, since spin trapping was absorbed in ESR spectra of Hp‐Ch film by the use of oxygen sensitive spin trapping reagent. An induced circular dichroism spectrum was observed only for Hp‐doped chitosan film over a range 360–450 nm among seven pairs of polymers and dyes; it is suggested that Hp molecules are arranged parallel along the carbohydrate backbone of chitosan, resulting in the highest acceptance of photo‐induced radical

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360409

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360413

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY