摘要:

AbstractA kinetic study on phase transitions from nematic mesophase to isotropic state for poly(p‐benzamide) (PBA)/H2SO4and poly(p‐phenyleneterephthalamide) (PPTA)/H2SO4systems was carried out by using depolarized light intensity (DLI) technique and polarised light microscopy (PLM) observation. The order of phase transition and activation energy were evaluated. The results indicated that the phase transition for both PBA/H2SO4and PPTA/H2SO4systems is a first‐order transition, and the polymer concentration and molecular flexibility have significant influence on the activation energy of the phase transition. The influences of concentration and molecular flexibility were discussed on the basis of the modified mean‐field

ISSN:0959-8103    

DOI:10.1002/pi.4990320402

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTensile, flexural and impact properties were measured of a heterogeneous polymer blend system, consisting of nylon 6 and a chemically modified ABS (MABS). It was found from the tensile tests that nylon‐richer blends show yielding behaviour and nylon‐leaner blends show necking behaviour. The addition of MABS increases the modulus, whereas the tensile strength and percentage elongation at break decrease and go through a minimum. The impact strength is increased to a maximum of approximately three times when 20 wt% of MABS is added to nylon 6. In order to interpolate the mechanical properties observed, empirical equations are given which are found to describe the experimental data rather well. Photomicrographs were taken of the tensile fractured surfaces using a scanning electron microsc

ISSN:0959-8103    

DOI:10.1002/pi.4990320403

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThis work reports on the microstructural study of the system: poly(ethylene oxide) (PEO) and a poly(fluoroalkoxyphosphazene) (PPz) and comprises both isothermal and non‐isothermal crystallization kinetics as a function of blend composition, as well as the analysis of spherulite growth, nucleating energy and nucleation density.In addition, compatibility studies were conducted based on glass transition temperature on the one hand, and on the other hand on the determination of the Flory‐Huggins interaction parameter via melting point depress

ISSN:0959-8103    

DOI:10.1002/pi.4990320404

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe structure of products resulting from the free radical copolymerisation of multimethacrylate—poly(vinyl methacrylate)—with acrylic acid was examined by the radiometric method. The copolymerisation was carried out in dilute solutions ofN,N‐dimethylformamide using 2,2′‐azobisisobutyronitrile labelled with14C as initiator. The results show that over 90% of methacrylate units react along the template chain forming ladder‐type blocks, while the remaining units branch or do not participate in

ISSN:0959-8103    

DOI:10.1002/pi.4990320405

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractButadiene‐acrylonitrile random copolymers with various molecular weights and end‐groups were introduced into a system consisting of the diglycidyl ether of bisphenol A (DGEBA) and 3,3′‐dimethyl‐4,4′‐diamino dicyclohexyl methane (3DCM) cured at 50°C. We studied the influence of a low level of soluble additive on the polymerization rate, evolution of viscosity, gelation and vitrification times, and the final network in the cases of different additive molecular weight and end groups of the additive. It was found that the additive influences the final network only by dissolving in the matrix and that the dilution effect plays a minor role, but the catalytic effect of an additive can play a significant role on the polymerization depending on the additive end groups. However, in all the rubber‐modified systems, the phase separation has no direct influence on the polymerization rate and the cha

ISSN:0959-8103    

DOI:10.1002/pi.4990320406

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe reaction‐induced phase separation in epoxy systems modified with rubber was firstly observedin situwith small angle X‐ray scattering (SAXS), light transmission (LT), light scattering (LS), scanning electronic microscopy and transmission electronic microscopy techniques. The different observation windows of the SAXS, LT and LS methods allow us to follow the phase separation at two size levels. The selected system was bisphenol‐A diglycidylether cured with 4,4′‐diamino‐3,3′‐dimethyldicyciohexylmethane, in the presence of 15% wt of epoxy‐terminated butadiene acrylonitrile random copolymers of different molecular weights. The phase separation inside the particles formed was followed first. Influences of precure temperature, rubber molecular weight, the postcure, vitrification and gelation on the evolution of the structure inside the particles are discussed. The real beginning of the phase separation

ISSN:0959-8103    

DOI:10.1002/pi.4990320407

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe dielectric constant, loss tangent and AC conductivity of solution grown cellulose acetate‐butyrate films of 5μm thickness were studied as a function of temperature (300‐450 K) in the frequency range 10 Hz‐10 MHz. The decrease in dielectric constant was observed with the increase in frequency as well as with temperature. A loss peak was observed in the dielectric loss spectra and was identified as the β‐relaxation peak. The frequency‐dependent conductivity was also studied. The results were interpreted in terms of electronic conduction via hoppin

ISSN:0959-8103    

DOI:10.1002/pi.4990320408

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTernary copolymerisation of glycidylmethacrylate (GMA), with different alkyl acrylates (methylacrylate (MA), methylmethacrylate (MMA), butylacrylate (BuA) andn‐butylmethacrylate (n‐BuMA)) and acrylonitrile (AN)) were carried out in solution at 65°C in the presence of a free radical initiator. Experimental terpolymerisation data agree well with calculations based on the Alfrey‐Goldfinger equation. The determination of unitary, binary and ternary azeotropes of the various systems studied was easily handled by a computer. Ternary azeotropic compositions for GMA‐MMA‐AN and GMA‐nBuMA‐AN systems were found to be 17‐50:68‐50:14‐00 and 51‐00:3‐00:46‐00 mol%, respectively. Also, 'pseudo‐azeotropic' regions were identified where the deviation between feed and polymer

ISSN:0959-8103    

DOI:10.1002/pi.4990320409

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe migration of the plasticizer, dioctyl adipate (DOA) in the accelerated ageing of composite propellant has been studied. The method is based on the extraction of DOA with carbon tetrachloride and its estimation by gas chromatography. The concentration of DOA in the propellant at different distances from the insulation was determined after a definite ageing period and compared with the initial DOA concentration. The effect of (a) the ageing period, and (b) the ageing temperature on the degree of migration was examined. The present studies confirm the existence of plasticizer migration in the propellant adjacent to the insulation, during ageing.

ISSN:0959-8103    

DOI:10.1002/pi.4990320410

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractSeveral series of polyaniline dispersions were prepared by oxidative polymerization of aniline in aqueous medium. Ammonium persulfate was used as an oxidizing agent and poly(vinyl alcohol) as a steric stabilizer of dispersions. The amount of dispersion particles their size and uniformity and the fraction of the steric stabilizer attached to the particles were determined in dependence on the concentration of the individual components and on temperature. The properties of resulting dispersions are controlled mainly by the concentration of the oxidizing agent and by the polyaniline/stabilizer ratio.

ISSN:0959-8103    

DOI:10.1002/pi.4990320411

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY