摘要:

AbstractThe temperature dependence of ultrasonic pulse velocityCand specific volume resistance ρvof crystallizing thermoplastic polyurethane (TPUR) was investigated. It was revealed that under certain conditions TPUR acquired abnormally low ρvvalues andCvalues uncharacteristic of polymers. An explanation for the observed abnormalities could be based on the assumption of the presence of ‘hot’ electrons in

ISSN:0959-8103    

DOI:10.1002/pi.4990300102

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe kinetics of formation of the [PVA. MnVIO 42−] intermediate complex have been measured by the conventional spectrophotometric technique. The rate of formation of the complex was found to be given by the expression d[Complex]/dt=k1[MnO‐4][PVA−]. The results showed that the rate of formation is dependent on the base concentration. A first‐order reaction in permanganate and fractional order with respect to the poly(vinyl alcohol) (PVA) concentration were observed. The activation parameters have been evaluated and a tentative reaction mechanism has been

ISSN:0959-8103    

DOI:10.1002/pi.4990300103

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractCastor oil (CO) was used to replace polydisperse commercial rubbers (carboxy‐ or epoxy‐terminated butadiene‐acrylonitrile random copolymers, CTBN or ETBN) in model systems developed to analyse the origin of the phase separation process in rubber‐modified thermosets. Mixtures of CO with an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) showed a higher miscibility than a typical CTBN (18% acrylonitrile)‐DGEBA system. Thermodynamic factors accounting for this behaviour are discussed using the Flory‐Huggins lattice model. Addition of a stoichiometric amount of ethylenediamine (EDA) to a DGEBA‐CO solution increased the miscibility. A pseudo‐binary approach was used to fit the cloud point curve up to 30% volume fraction of CO. Percentage conversions at the cloud point during the DGEBA‐EDA polymerization were experimentally determined and compared with theoretical predictions using the pseudo‐binary approach in the framework of the Flory‐Huggins lattice model. Reasonable agreement was found, giving direct evidence of the fact that phase separation results from the decrease in the entropic contribution to the free energy of mixing

ISSN:0959-8103    

DOI:10.1002/pi.4990300104

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of different annealing time/temperature regimes on the thermal and crystalline behaviour of a series of statistical copolyamides (nylon 8/nylon 12), prepared by activated anionic polymerization of octanelactam/laurolactam (OL/LL), were determined by DSC, X‐ray (WAXS), density and viscosity measurements. The melting temperature and the heat of melting increased with annealing time and temperature. The results were correlated with the molar composition of the copolyamides and showed a gradual increase in percentage crystallinity with tim

ISSN:0959-8103    

DOI:10.1002/pi.4990300105

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRaman spectroscopic studies of the dissolution of polyacrylonitrile (PAN) in aqueous zinc halides are reported. The dissociation constants of aqueous PAN‐zinc chloride and PAN‐zinc bromide containing 60‐75% wt/wt and 65‐80% wt/wt zinc in aqueous polyacrylonitrile solutions, respectively, have been measured by Raman spectroscopy. Intensity measurements allowed for a quantitative measurement of the amount of free and complexed CN groups to be made, utilising the 2259 and 2290cm−1v(CN) stretching Raman bands. The degree of complexation was found to be small in many of the solutions. The effect of the addition of salt on the structure of thev(OH) band at 3000‐3800 cm−1was studied for the aqueous zinc salts and an aqueous sodium thiocyanate solution. The low wavenumber regions of the Raman spectra, Δv = 100‐350cm−1, for both zinc chloride and zinc bromide solutions of PAN have

ISSN:0959-8103    

DOI:10.1002/pi.4990300106

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractMetal complexes of thiophosphorylated cellulose, when heated, give rise to high char yields. These and related observations suggest that such derivatisation may give rise to novel flame retardant treatments for cellulosic materials.The kinetics of thermal degradation of cellulose, cellulose ethylthiophosphate (CESP) and metal complexes of the CESP have been studied by thermogravimetry (TG) and differential thermal analysis (DTA) from ambient temperature to 700°C in dynamic air to investigate the potential flame retardance of the CESP and its metal complexes. Various parameters such as energy, entropy, enthalpy and free energy of activation have been calculated using the Broido method and transition state theory. For the decomposition stage of thermal degradation, the activation energies of the CESP samples lie in the range 53‐133 kJmol−1and of the metal complexes, 108‐177kJmol−1, which are found to be lower than that of cellulose (187 kJmol−1). Scanning electron micrographs of the CESP show that the fibrillar structure of cotton has become more evident and chars retain the general morphology of the original fibre although severe, localised zones of damage reflect the gross chemical and physical changes occurring during pyrolysis. The IR spectra of chars of modified samples indicate formation of compounds containing C=O, C=C and P=O groups. The mechanisms of thermal degradation of the CESP and its metal complexes have bee

ISSN:0959-8103    

DOI:10.1002/pi.4990300107

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe morphology, microstructure and compatibility of binary and ternary polyblends based on poly(vinylidene fluoride) have been studied by means of glass transition temperature, isothermal crystallization kinetics analysis and scanning electron microscopy in order to determine the possibilities offered by poly(vinyl acetate) for compatibilizing poly(vinylidene fluoride) and polystyrene. Calorimetric and dynamic mechanical analyses demonstrate that poly(vinyl acetate) tends to ‘compatibilize’ blends of PVF2/PS, although the results of the two analyses do not agree with each other; we presume that this is due to differences in the techniques emplo

ISSN:0959-8103    

DOI:10.1002/pi.4990300108

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe design of delayed action heat seal adhesives depends on the physical properties of the polymer, plasticiser and their resultant mixtures. This paper explores the relationships between various molecular interactions and the performance of the adhesives. Dielectric relaxation measurements of mixtures of poly(vinyl acetate) or polystyrene and a plasticiser, dicyclohexyl phthalate, were performed to characterise the molecular dynamics of the system. Binary mixtures over the entire composition range were examined from 244 to 408 K and over a frequency range from 10−1to 6 × 104Hz, and allowed the nature of the interaction between plasticiser and polymer to be quantified. Dielectric studies are compared with measurements of the glass transition temperature obtained using thermal and mechanical analysis, and indicate that over certain composition ranges segregation of the components occurs at a molecular level. These observations are discussed in relation to the design of a delayed action heat seal formulati

ISSN:0959-8103    

DOI:10.1002/pi.4990300109

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThree 4‐hydroxyphenylmaleimide/n‐butylacrylate (HPMI/n‐BuA) copolymers with different monomer ratios were synthesized. Their average molecular weights, glass transition temperatures (T,g), and thermal decomposition temperatures were measured. It was found that these copolymers had higher average molecular weights and higher thermal decomposition temperatures than novolac.Modified phenolic resins were prepared by transfer moulding from moulding compounds consisting of novolac, the copolymer, hexamethylenetetramine (hexamine), and glass fibre. Properties of the three kinds of modified phenolic resins were examined by flexural test, impact test, dynamic thermomechanometry, and observation of morphology. It was found that phenolic resin modified with HPMI/n‐BuA (1/3‐6) copolymer and modified with HPMI/n‐BuA (1/7‐0) copolymer showed good toughness and good heat resistance. It was also found that the heat resistance of modified phenolic resins was improved by after‐cure, but the mechanical properties were decreased by after‐cure: similar behaviour was observed for unmodifi

ISSN:0959-8103    

DOI:10.1002/pi.4990300110

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractMethyl methacrylate (MMA) was polymerized by thiophenol without oxidants. Hydroquinone had no effect on the polymerization, indicating that the polymerization proceeded via a non‐radical process. Since other monomers with anx,β‐unsaturated carbonyl group polymerized similarly, the initiation and propagation were explained by the Michael addition. Radical scavengers such as 1,1‐diphenyl‐2‐picrylhydrazyl(DPPH) and galvinoxyl enhanced the polymerization because of an accompanying radical polymerization initiated by radical species formed by the reaction of them with thiophenol. Aluminium acetylacetonate, which has no effect on radical polymerization, accelerated the thiophenol‐initiated polymerization supporting the postulat

ISSN:0959-8103    

DOI:10.1002/pi.4990300111

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY