ISSN:0007-1641    

DOI:10.1002/pi.4980180502

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractA new procedure for the glycidylation of aromatic amines has been developed recently, which leads to resins of lower viscosity, longer shelf‐life and higher purity than methods used previously. Resins made by the new process show considerable processing and applications advantages over those made by earlier methods. The new process has also made accessible high purity glycidyl derivatives of amines which have hitherto proved difficult to glycidylate effectivel

ISSN:0007-1641    

DOI:10.1002/pi.4980180503

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe effect of structure, composition, and cure on the water absorption andTgof amine‐cured epoxies was investigated. Water absorption is considered to depend on the polar group concentration and type, and on the amount of free volume in the polymer network. The contribution of polar groups in terms of their hydrogen bonding capabilities is reflected by the effect ofmeta(with respect to the diglycidylamino group) chloro, bromo, and methyl substituents on the water absorption of bis[N,N‐bis(2,3‐epoxypropyl)‐4‐aminophenyl]methane cured with 4,4′‐diaminodiphenylsulphone. The observed water absorptions are in line with the expected electronic effects of the substituents on the basicity of the amine group. Substituents in theorthoposition adversely affect the hydrogen bonding capability of the amine group and limit the extent of reaction by steric interference. Examination of fourO‐glycidyl systems (Epon 825, Epon 1153/114, Epon 1031, and Dow XD‐7342) cured with 4,4′‐diaminodiphenylsulphone has revealed quite a good linear relationship between the equilibrium water absorption andTgfor a particular hardener concentration irrespective of the epoxy compound employed. Networks ranged from those of lowTg(110°C) and water absorption (1.3%) to those of high values (300°C and 6.1%) for these parameters. Differences in slope for low (50‐65%) and high (100%) stoichiometric amounts of hardener are attributed to differences in the relative importance of OH/epoxy and NH2or NH/epoxy reactions. The theoretical polar group concentrations and polar group type are much the same for these different systems and thus, free volume is considered to be a function ofTgand to play an important part in determining the

ISSN:0007-1641    

DOI:10.1002/pi.4980180504

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe effect of relatively severe hygrothermal aging on the sorption and also the diffusion of water at 40°C has been studied for a number of epoxy networks comprising tetraglycidyl 4,4′‐diaminodiphenyl methane, and the curing agent 4,4′‐diaminodiphenyl sulphone, 4,4′‐diaminodiphenyl methane and 2,2′‐dichloro‐4,4′‐diaminodiphenyl methane. Aging at high temperatures is accompanied by a pronounced increase in sorptive capacity at 40°C consistent with a significant expansion of the network. Dry annealing of the aged network at sub‐Tgtemperatures collapses the expanded structure to recover the sorptive capacity of the unaged network. Preliminary studies of the sorption‐desorption kinetics for aged networks indicate that the effective diffusion coefficie

ISSN:0007-1641    

DOI:10.1002/pi.4980180505

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe development of low toxicity rigid epoxy foams as an alternative to polyurethane foams for electronics encapsulation is described. The basic foam components ‐ epoxy resin, hardener, accelerator, blowing agent and surfactant ‐ are blended to form a two part system which is mixed and foamed when required. Each foam component is selected for its contribution to the foaming reaction and the final foam properties. The balance of component miscibility, viscosity, reaction rate and exotherm determine foam quality. Foam properties are affected by (1) density (2) cell structure and (3) the molecular structure of the reactants. Initial foam development utilised epoxy/amine chemistry and produced two foams, Feldex F3 and F4. Subsequently, use of a more reactive polymercaptan hardener improved foam strength and process times, resulting in Feldex F5 and F6 which have been used successfully to prepare quality mouldings and encapsulated electronics. Recently, development has been extended to new areas of application, e.g. high temperature foams. The mechanical, electrical, thermal and chemical properties of the best epoxy foams have been evaluated; selected results are reported. The epoxy foams developed offer low density, high strength, low dielectric constant and loss tangent, high volume resistivity, good thermal insulation, low corrosivity and low toxicity. In addition, epoxy foams soften in acetone, an advantage over their polyurethane counterparts since encapsulated electronics may be retrieved without employing corrosive solvents. (Feldex is a registered trade mark of THORN EMI Electroni

ISSN:0007-1641    

DOI:10.1002/pi.4980180506

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe reaction between phenylglycidyl ether and a number of substituted imidazoles has been investigated using a combination of tritium nuclear magnetic resonance spectroscopy and radio‐high performance liquid chromatography, two methods that have not been used previously in this area. For more volatile catalysts such as aromatic amines radio‐gas chromatography can be employed to good eff

ISSN:0007-1641    

DOI:10.1002/pi.4980180507

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractCarefully designed resin precursors of high purity, viz.N,N‐bis‐(2,3‐epoxypropyl)‐N',N‐dimethyl‐4,4′‐diaminodiphenylenemethane (G2A) andN,N‐bis‐(2,3‐epoxypropyl)‐N,N‐dimethyl‐4,4′‐diamino‐diphenylenemethane (G2S) were used in combination withN,N,N',N‐tetrakis‐(2,3‐epoxypropyl)‐4,4′‐diaminodiphenylene methane, TGDDM, and cured with stoichiometric amounts of 4,4′‐diamino‐diphenylene methane (DDM) to produce networks with a range of controlled crosslink density. The tensile moduliEof the networks in the rubbery state, atTg+30°C,Tg+45°C andTg+60°C, were measured using a thermal mechanical analyser. Using the statistical theory of rubber elasticity and the observed values ofE, the number average molecular weights between crosslink pointsMcfor the cured resins were deduced. The experimentalMcvalues were then compared with those derived by calculations based on a probabilistic model of the network proposed by Chu and Seferis.1The experimentalMcvalues were 2.5 to 5.5 times larger than the calculated ones. The differences were attributable to a consumption of only 40% of the available secondary amino hydrogen via epoxy‐amine reaction. A direct relationship was established between the glass transition temperature and the crosslink density 1/Mcfor the resins, and the dynamic mechanical properties were studied. The thermal stability of cured resins studied by thermo‐gravimetric analysis indicated an enhancement of stability as 1/Mcwas reduced. The amount of water

ISSN:0007-1641    

DOI:10.1002/pi.4980180508

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper deals with the modelling of the hydrolysis of benzylpenicillin to 6‐aminopenicillanic acid (6‐APA) and phenyl acetic acid (PAA) in a small pilot plant batch recirculated reactor by an immobilised penicillin amidase preparation. By using the following linearised form for an integrated Michaelis‐Menten equation Et/V0X=α+β| In (1‐X)/X| where α and β are reaction kinetic parameters, good correlations are obtained of α and β with linear velocity across the reactor, substrate concentration and temperature of operation. A process to determine α and β from initial velocity measurements is outlined. The applicability of the above equation to published data i

ISSN:0007-1641    

DOI:10.1002/pi.4980180509

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper is concerned with the development of a model to plan a strategy for an enzymatic batch process whereby the enzyme is subjected to deactivation as described by the exponential (first‐order) decay model. The particular system used was the enzymatic hydrolysis of penicillin to 6‐aminopenicillanic acid, but the model can be utilised with other batch systems, provided that decay of the immobilised enzyme preparation is described by the exponential decay model. The model developed is eminently practical and simple, and several examples of its application are given. Experimental data obtained in a small pilot plant batch recirculated reactor could, on average, be well fitted by this mo

ISSN:0007-1641    

DOI:10.1002/pi.4980180510

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe effects of crosslink enhancement by the presence of acetylene during gamma irradiation, on the physical and mechanical properties of polypropylene film are reported. Gel contents show that crosslink enhancement is considerably greater if the sample is highly annealed (PPA) than if it is quenched (PPQ). For PPA, thermal analysis suggests only minor damage to the crystalline lamellae, but significant stabilisation of lamellae by crosslink formation in the lamellar surface regions. This is supported by an increased resistance to the yielding process observed in tensile stress/strain and creep tests. The effects in PPQ is less.

ISSN:0007-1641    

DOI:10.1002/pi.4980180511

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY