摘要:

AbstractDue to the difference in reactivity between free isocyanates and uretdione rings, diisocyanate dimers can be used as blocked isocyanates. They offer the potential advantage that no volatile by‐products are formed. The toluene 2,4‐diisocyanate dimer contains one uretdione ring, formed by dimerization of two isocyanate groups, and two free isocyanate groups. The latter react rapidly with the hydroxy groups of a polycaprolactone diol at temperatures above 80°C. The pure dimer thermally dissociates above 150°C; dissociation is reversible. In the presence of OH groups, the regenerated isocyanate groups can then react to form urethanes. Our experiments have also revealed the formation of allophanate groups as reaction products of an uretdione ring with a hydroxy group. The influence of initial molar ratio of reactants and of temperature on the mechanisms have been discussed. Allophanates are not stable at high temperature in presence of remaining hydroxy groups, their dissociation leads to urethanes. Application of branching theory has shown that the system can gel due to allophanate formation in a wide range of initial molar ratios of NCO to OH g

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420101

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe effect of alumina particulates on a thermoplastic matrix is investigated, in particular the effect altering the alumina particle size and morphology has on the mechanical properties. Different grades of alumina are used and two thermoplastic matrices; namely poly(propylene) and poly(ethylene‐co‐vinyl acetate). Investigations showed that optimum properties were achieved with the alumina of smallest particle size and lowest aspect ratio. Preliminary work has also been performed on the use of silane coupling agents and they have proved effective in increasing the tensile properties of the composi

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420102

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractBased on an earlier paper of Chen and Lee, a procedure is developed to determine optimal reaction times for predetermined monomer conversions and number‐average degrees of polymerization in an azeotropic free‐radical batch copolymerization with one charge of monomers and initiator. The procedure allows for the calculation of the admissible range of monomer concentrations, the determination of an appropriate initiator and its most suited concentration to arrive at the goal in reaction times as short as possible. The validity of the model was tested in the free‐radical copolymerization of acrylonitrile and butadiene in chlorobenzene at 343 K, using 1,1′‐azocyclohexanenitrile (ACN) and 2,2′‐azoisobutyronitrile (AIBN) as initiators. The agreement of theoretical and experimental data was satisfying. It is pointed out that the gel effect can be incorporated into the model, and that the procedure can also be used in the design of free‐radical homo

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420103

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractL'étude préliminaire des propriétés microlithographiques des résines obtenues en mélangeant un polyimide et un bis‐azide a permis de montrer que de telles résines pourraient probablement être utilisées en tant que résines microlithographiques sensibles aux UV lointains. En effet ces résines donnent des couchages homogènes qui ont des épaisseurs convenables. De plus, elles sont très sensibles aux irradiations: elles subissent alors des modifications de structure lorsqu'on les irradie par des radiations de longueur d'onde égale à 254 nm. Les parties ainsi insolées sont insolubles dans les solvants constitués par des mélanges d'eau et de dioxane ou d'eau et de 1‐N‐méthylpyrrolidone alors que ces mêmes solvants solubil

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420104

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractEight samples of poly(ethylene‐co‐propylene‐co‐diene) (EPDM, containing 55 wt.‐% ethylene) were vulcanized with 0.5–8.0 phr dicumyl peroxide. The influence of molar volumes V1of cyclohexane, hexane, heptane, iso‐octane, tetrachloromethane, carbon disulfide, xylene, benzene, toluene, tetrahydrofuran, trichloromethane and chlorobenzene on the swelling intensity of the EPDM vulcanizates was studied, and it was found that regardless of the solubility parameters, polarity, dielectric constants, acidity or basicity of solvents, a linear relationship exists between V1and number of moles of solvent in the gels, n1. With increase of V1

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420105

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractTrimethylammonium‐2‐hydroxypropylxylans with degrees of substitution (DS) ranging from 0.25 to 0.98 were hydrolysed to monomer units, and the13C NMR spectra of the hydrolysates as well as products separated therefrom were taken and assigned. Monosubstitution of the xylose units was found mainly to occur in the studied DS range. At lower DS, substitution of OH‐2 groups is preferred, whereas at higher DS the regioselectivity is

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420106

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractEmulsion polymerization of ethyl acrylate was carried out in the presence of different kinds of functionalized and non‐functionalized silica particles. 3‐(Trimethoxysilyl)propyl methacrylate, 2‐hydroxyethyl methacrylate and 3‐(triethoxysilyl)‐propanethiol functionalization agents were examined. It is demonstrated that use of the first two coupling agents results latexes able to give films which display remarkable mechanical properties similar to those of vulcanized elastomers reinforced with solid particles. A qualitative model is then set up to give account for these properties. It is proposed that a part of the polymer is covalently bound to silica as tight loops, giving rise to a set of strong entanglements with the non‐grafted polymer during film formation. This model is supported by stress‐strain measurements. Some validation experiments are described using the third grafting agent

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420107

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe present paper deals with studies concerned with an optimization of the synthesis of urethane‐acrylic UV‐cured resins intended for application as protective coatings for optical fibers. Oligoetherdi‐ and triols, toluylene diisocyanate and isophorone diisocyanate, as well as hydroxyethyl methacrylate and hydroxypropyl methacrylate were used for synthesis. Active diluents butyl acrylate, 2‐ethylhexyl acrylate, 1,4‐butanediol diacrylate or their mixtures, and 2,2‐dimethoxy‐2‐phenylacetophenone as a photoinitiator were added to the urethane‐acrylic dimers comprising polymerization‐active double bonds. The compositions were characterized by the determination of density, viscosity, refractive index, gel content, glass transition temperature, Shore hardness, Young's modulus, breaking stress, relative elongation at break, thermal resistance and water vapour diffusion coefficient before and after curing.The utility of these compositions for protective intermediate coatings of optical fibers was checked and confirmed under manuf

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420108

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractNo radicals are formed in bis(mercaptopropionate)‐diene‐mixtures, as shown by means of ESR spectroscopic investigation. Radicals are produced spontaneously only in the presence of triethylene glycol dithiol. The hydrogen‐bonded structure of the dithiopropionates is obviously responsible for the inhibition of the charge transfer interaction with the diene compounds and prevents subsequent radical formation. The13C NMR spectra confirm the anti‐Markownikow structure of the polymers formed with diallyl succinate and diallyl tereph

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420109

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractPolymer matrices were prepared by suspension polymerization of 2‐hydroxyethyl methacrylate, dodecyl methacrylate and ethylene glycol dimethacrylate. It was shown that porosity decreased with the addition of monomers with hydrophobic side chains. Trypsin, bovine serum albumin and lipase served as standard proteins in sorbent hydrophobicity evaluation. Isocratic chromatography at various ionic strengths revealed different elution behaviours. Some sorbents exhibited an ion‐exchange mode in the whole range of ionic strength variation. Some others showed a hydrophobic interaction character when the salt concentration exceeded a critical value. It is suggested to take this critical salt concentration as a relative measure of hydrophobicity for particular protein‐matrix‐salt systems. It was shown that the matrix containing 90 μmol/g of dodecyl methacrylate was enough hydrophobic to differentiate proteins and thus could be used effectively for hydrophobic interaction chromatography of

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052420110

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY