摘要:

AbstractThe observation of various features of living polymerizations (‘theoretical’ molecular weights, narrow molecular weight distribution) in a large number of carbocationic polyerizations has led to the conclusion that termination and transfer were suppressed in these ‘living’ systems, while they played a predominant role in the ‘classic’ carbocationic polymerizations. This suppression has been attributed to the presence of new types of active sites, such as ‘stretched’ covalent bonds or ‘stabilized’ carbocations.In the present article, a comparison of the data observed with the ‘classic’ and the ‘living’ systems shows that the active sites are similar, with only a change in the relative proportion of carbocationic species, which reduces the rate and favors complete initiation. This means that these ‘living’ systems are generally only apparently living, since termination and transfer reactions also occur and are hidden because the molecular weights of the ‘living’ polymers are typically low. Transfer and termination may, however, be considerably reduced or even suppressed by working at very low temperatures, as is

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350101

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA systematic spectrophotometric study on the complexation of chromium (III) ion with sodium carboxymethyl cellulose (CMC) was carried out. The effects of the degree of substitution (DS) of the polymer, the concentrations of Cr(III) and CMC solutions, the pH and temperature on the complex formation were studied in the aqueous state. CMC complexes with Cr(III) were characterized by elemental analysis, magnetic moment and spectral (Vis and IR) data. The results showed that CMC (L) chelated to the metal ion according to the formula CrL2· 2H2O. The ligand field parameters, namelyDq,Band β were calculated; the β‐values indicate strong covalency in the ligand σ bond. The IR spectra revealed that the chelating sites of CMC are not only the carboxymethyl groups, via the ether‐ and the carboxyl‐oxygen atoms, but also the secondary hydrox

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350102

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe optimum reaction conditions for the deposition of smooth conductive polypyrrole (PP) films were monitored using a quartz crystal microbalance technique. This is for oxidative polymerization of pyrrole with some iron(III) compounds. The FeCl3· 6H2O/pyrrole system in aqueous solution at 20 ± 0.5°C was examined in some detail. The effect of the initial molar ratio of the reactants on the yield and the growth rate of the PP film deposition was studied. The optimum molar ratio was found to be approximately 2.4 ± 0.1. A comparison between the growth rate of the PP films was made when different iron(III) compounds were used. The rate is shown to be affected by the nature of the anions in these compu

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350103

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPoly(1‐olefin sulphone)s have been prepared from olefins with a chiral centre at the carbon atom adjacent to the double bond. In13C and1H NMR studies on the polymers obtained by free radical copolymerisation it has been found that the chirality of a main chain methine carbon that forms part of the backbone depends upon the chirality of the carbon initially present within the same hydrocarbon residue. The introduction of bulky groups into the chiral group of the monomeric olefin increased the ratio of diastereoisomers formed within the residue. In the most favoured case 69% of the backbone chiral centres were fixed with reference to the side chain structures. By employing a simple theory based upon an enumeration of steric interactions and upon the γ‐gaucheeffect on carbon chemical shifts, it was deduced that the main chain chiral centre preferred to adopt the opposite stereochemistry to that of the side chain when that carries an ethyl group, a methyl group and a hydrogen atom. A bias was also found at the backbone when the monomer chiral centre contained polar acid or ester gr

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350104

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA series of collagen–polypyrrole hybrid materials have been synthesized by the chemical polymerization of pyrrole using FeCl3as initiator in the presence of soluble collagen. The black color of the resulting materials indicates the presence of polypyrrole while collagen was verified by amino acid analysis of the hybrids. Collagen incorporation into the hybrid was found to be a function of pyrrole concentration used in the polymerization. When the concentrationof pyrrole was high, the collagen loading was low and vice versa. This inverse relationship was also found in the hybrids' electrical conductivity. A 26% collagen content in the hybrid gave a conductivity of 1.4 S cm−1while a 4% collagen gave a higher value of 62.4 S cm−1. Thermogravimetric data suggest that the two polymers exist in the hybrid as a blend. The nature of the interaction of the components in the hybrid is believed to be strong since collagen could not be extracted despite denaturation with sodium dodecylsu

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350105

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe hardness of ‘late’ and weakly crosslinked polymethylmethacrylate was determined experimentally. As the time of the addition of the cross linker to the polymerizing polymer increases, the hardness first increases, passes through a maximum and then decreases. This change can be expressed by an asymmetric curve. The change of hardness is expressed in terms of a theoretical equation based on the distribution of chains. Some scaling relationships were obtai

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350106

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe easily accessible, water soluble, conjugated polymer poly(4‐bromopyridine), has been synthesised by the self‐condensation of 4‐bromopyridine at various temperatures and also in the presence of methyl iodide. The structure of the material is complex with a variety of sub‐units; possible structures are discussed in the light of a detailed spectroscopic a

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350107

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractAn experimental study was carried out to demonstrate the possibility of compatibilising blends of polyvinylidenefluride with minor amounts of fluorosilicone elastomer, thereby achieving better low temperature ductility without excessively reducing the melting point and degree of crystallinity of the fluoropolymer.The principle that has been explored is the use of multifunctional crosslinking agents acting as a common solvent for the two polymers during mixing, and providing interpenetrating networks through the two polymer phases by means of peroxide‐induced crosslinking reactions.It has been found that mixtures of triallyl isocyanurate with diallyl phthalate are particularly effective in compatibilising the combination of polymers in question, giving the best overall balance of properties. Compatibilisation was enhanced by grafting part of the coagent on to the chains of the fluoropolymer prior to being blended with the fluorosilicone gum. Further evidence for enhanced compatibilisation by such a procedure was obtained from dynamic mechanical tests, which revealed an increase in glass transition temperature for the fluorosilicone phase and a suppression of α‐relaxations in the fluoropolymer compo

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350108

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPoly(2‐methoxycyanurate) of bisphenol F and bisphenol A (PMCBFA) was synthesized and fractionated by a fractional precipitation method. The fractions were characterized by viscometry, osmometry and gel permeation chromatography. The Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were established in four solvents and at four different temperatures. The unperturbed dimensions and their coefficients in different solvents were computed using the Stockmayer–Fixman excluded volume theory. From the solution study it was found that PMCBFA is highly flexible. This may be due to the ether linkage present in the m

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350109

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolyaniline was electrochemically synthesized in the emeraldine oxidation state and then converted to the pernigraniline oxidation state by applying an electric potential under optimized conditions. The stability/reactivity of polyaniline in the pernigraniline oxidation state was evaluated in various aqueous media. The products of the reduction of the pernigraniline oxidation state byo‐toluidine were analyzed by gel permeation chromatography, ultraviolet–visible and infrared spectroscopies, and cyclic voltammetry. The results are consistent with the synthesis of a diblock copolymer of polyaniline/poly(o‐toluidine) and also of some poly(o‐toluidine) homopolymer in the emeraldine oxidation state as a side

ISSN:0959-8103    

DOI:10.1002/pi.1994.210350110

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY