摘要:

AbstractMean‐square dipole moments for styrene/4‐vinylpyridine (S4VP) random copolymers were determined at five different temperatures, 25–60°C, in 1,4‐dioxane solution. The dipole moment behaviour was examined with respect to the increase in mole fraction of the polar monomer, 4‐vinylpyridine (4VP), in the copolymer. The behaviour observed was different from the general behaviour of similar copolymers.The temperature coefficient of the dipole moment ratio was found to be zero, within experimental error, in the temperature interv

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330301

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractBy means of the gelation equation containing both inter‐ and intramolecular reaction parameters obtained by the authors, this paper deduces the gelation range of Aai–Bbjtype polycondensation. The experimental data are essentially in agreement with our theoretical resu

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330302

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe adsorption behaviour of some ethoxylated alkylphenol–formaldehyde polymeric non‐ionic surfactants, at the aqueous solution–air interface, was investigated by measuring the surface tension (γ) as a function of concentration (C) at four temperatures. By applying the Gibbs adsorption equation to the γ versusCdata, the adsorption isotherms of these polymeric surfactants were obtained.Surface concentration (Λ) of the investigated polymeric non‐ionics was found to increase with decreasing temperature and decreasing hydrophobic group (R) chain length, while varying the length of polyoxyethylene chain (%EO) appeared to have an insigificant effect. Effects of temperature, %EO and chain length R on the surface pressure (π) of the surfactant solutions were also i

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330303

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe effect of varying the rubber molecular weight on the reaction induced phase separation taking place in rubber‐modified epoxies is reported. Three butadiene–acrylonitrile copolymers with number‐average molecular weights of 2030, 3600 and 6050 g mol−1were used. The thermosetting polymer was an epoxy based on diglycidylether of bisphenol‐A cured with a cycloaliphatic diamine. Increasing the rubber molecular weight showed the following effects: (i) a decrease in the conversion at the cloud point; (ii) a corresponding decrease in the viscosity at the cloud point; (iii) a primary morphology of a low concentration of particles with a large size; (iv) a more complete segregation of the rubber from the matrix leading to a smaller decrease of the glass transition temperature of the system; (v) a decrease in the toughening. The Flory–Huggins lattice model may be used as a simple approximation to describe the phase separation process when varying the rubber molec

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330304

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractFour reactive liquid rubbers with different end‐groups but the same main chain (carboxyl‐, epoxy‐, amino‐terminated and non‐functional butadiene–acrylonitrile random copolymers) were employed in the same epoxy system, the diglycidyl ether of bisphenol A and 4,4′‐diamino‐3,3′‐dimethyldicyclohexyl methane cured at 50°C. The effects of the end‐groups of the liquid rubber on the morphology, phase compositions, sub‐structure inside the particles, interface between the phases and the mechanical properties were determined. The effects were related to the reactivity and the m

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330305

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractMixtures of methyl methacrylate (MMA) withN‐vinyl‐2‐pyrrolidone (VP) of various composition in the presence of fixed concentration of ethylene glycol dimethacrylate (EDMA) have been copolymerized to 100% conversion by γ‐irradiation. The resultant solid xerogels were swollen in water to yield hydrogels of equilibrium water contents ranging from 15 to 76wt%. The state of water in the poly(MMA‐co‐VP) hydrogels has been studied by differential scanning calorimetry (DSC) and the percentages of free freezing, freezable bound and nonfreezing water were found to vary with the xerogel composition, i.e. the degree of hydration of the hydrogels. At low equilibrium swelling, most of the water exists as a non‐freezing type, whereas at higher equilibrium swelling the majority of water exists as free freezing water. The maximum number of non‐freezing water molecules per VP unit in the hydro

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330306

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe crystallization and melting behaviour of two sets of ethylene/1‐butene copolymers have been analysed by DSC. The samples, with comonomer content in the range from 0 to 21.5 mol%, were obtained by industrial processes using both Mg/Ti‐based catalyst systems. The composition dependences of melting and crystallization temperatures were found to be strictly affected by the catalyst type. Moreover, logarithmic plots of the melting and crystallization enthalpy as a function of the ethylene content (mol%) in the copolymers fitted linear relationships whose slopes have been related to the critical sequence length of crystallizable ethylene units, depending on the catalytic system. These results are compared with those reported in the literature for ethylene/1‐butene copolymers synthesized by other catalysts and are accounted for by a different distribution of the comonomer units in the macromolecules of the two sets of sa

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330307

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA study has been made of radiation‐induced grafting of vinyl acetate (VAc) on to (tetrafluoroethylene–perfluorovinyl ether) copolymer (PFA). Effects of grafting conditions such as inhibitor and monomer concentrations and irradiation dose on the grafting yield were investigated. In this grafting system, ammonium ferrous sulphate (Mohr′s salt) was added to the monomer‐solvent mixture to minimize the homopolymerization of VAc and the most suitable concentration was found to be 2.0 wt%. It was found that the dependence of the initial grafting rate on monomer concentration is of the order 1.5. The degree of grafting tends to level off at high irradiation doses due to the recombination of formed free radicals without initiating graft polymerization. Some properties of the prepared graft copolymer such as swelling behaviour, electrical conductivity, thermal and mechanical properties were also investigated. The electrical conductivity was improved by hydrolysis of poly(vinyl acetate) in the grafted chains to their respective vinyl alcohols. The tensile properties were improved by grafting; however, the elongation percent decreased. The DTA data showed thermal stability of such graft copolymers for temperatures up to 300°C, but stability decreased at higher temp

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330308

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe dipolar relaxation mechanisms in poly(vinyl acetate) have been studied in detail using the technique of thermally stimulated currents. The papers published in the literature about this subject are very contradictory, particularly with respect to the assignment of the observed discharges to the corresponding motions at the molecular level. This work aims at clarifying these problems. We detected and characterised three different relaxation mechanisms: (1) a low temperature one (around −140°C) which was attributed to local internal rotations in the acetate side‐groups; (2) a relaxation whose maximum occurs at 42°C, which corresponds to the glass transition relaxation, and shows a compensation behaviour; (3) an upper glass transition relaxation whose maximum appears at 87°C and was attributed to a liquid‐liquid transition. These assignments have been made on the basis of the analysis of the behaviour of the samples when submitted to different thermal and electrical tr

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330309

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractHomopolymeric polyacrylonitrile and fibre‐forming copolymers containing either vinyl acetate or methyl acrylate comonomer have been studied by thermal analysis (DSC, TGA and DTG) at various heating rates (10–100 K min−1) and under air and nitrogen. Three well‐defined pyrolysis stages have been observed which occur over the temperature ranges 250–350°C, 350–550°C and above 550°C. Each stage involves a competition between volatilisation and cyclisation or char‐forming reactions which depends on heating rate and the presence or absence of oxygen.The well‐established dominance of cyclisation in the 250–350°C temperature range obtained during carbon fibre production from acrylic precursors occurs only at low heating rates. At high heating rates, volatilisation dominates and this explains why acrylic polymers have high flammabilities when heating rapidly.The full pyrolysis mechanism has been semi‐quantitatively analysed and the role that comonomers play discussed. This has enabled a fuller understanding of the potential burning behaviour of these p

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330310

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY