摘要:

AbstractWe studied alcoholysis of vinyl acetate and itaconic acid (up to 8.5 mol %) copolymers. We obtained the copolymers both by single and continuous addition of the second comoner, and carried out the alcoholysis in methanol and methanol‐gasoline medium at temperature 30°C using sodium hydroxide as catalyst. We established that the presence of itaconic sequences in the vinyl acetate polymer chain in an amount of 1.5–2 mol % causes significant reduction in the viscosity of methanol solutions without greatly affecting the molecular weight of the copolymer. The alcoholysis of random copolymers, containing not more than 4 mol % itaconic sequences takes place at a higher rate. The vinyl acetate‐vinyl alcohol copolymer, containing groups of itaconic acid has better surface activity. This is more clearly expressed in the case of random copo

ISSN:0021-8995    

DOI:10.1002/app.1990.070390701

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe objective of the research is to investigate epoxy resins where crosslinks formed in curing reactions can be cleaved and reformed without significant sacrifice in resin properties. In this phase of the investigation, experimental disulfide‐containing crosslinking agents have been studied, including dihydrazides of dithiodicarboxylic acids(aliphatic and aromatic) and dithio‐aromatic diamines. Conditions for curing reactions and for subsequent cleavage of crosslinks by reduction have been determined in model systems and confirmed for a prototype epoxy resin. A preliminary comparative evaluation of cure kinetics and of crosslink density and thermal and mechanical properties has been carried out for this resin cured with aromatic curing agents (4,4′‐dithiodianiline and methylene dianiline) and with aliphatic compounds (3,3′‐dithiopropionic acid dihydrazide and hexamethylene diamine). It has been shown that in a resin fully cured with disulfide‐containing crosslinking agents, crosslinks could be ruptured by reduction, and reestablished by oxidation under mi

ISSN:0021-8995    

DOI:10.1002/app.1990.070390702

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractEpoxy resins of varying epoxy equivalent weight were crosslinked with 4,4*‐dithiodianiline (DTDA) at a 2/1 mole ratio. Resin of equivalent weight 190 (Epon 828) was cured with DTDA at mole ratios varying from 2/1 to 1.25/1. Properties of cured resins were evaluated and their reduction was investigated. Under the conditions used, reduction to the point of complete solubilization was possible providing crosslink density did not exceed a threshold value tentatively established asMc= 400 −; 500. Recurring of reduced resins was accomplished by oxidation and by reaction of thiol groups with polyfunctional reagents, including bismaleimides and polyepoxi

ISSN:0021-8995    

DOI:10.1002/app.1990.070390703

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractIn an attempt to toughen the epoxy resin matrix for fiber‐reinforced composite applications, a chemical modification procedure of a commercially available bisphenol‐A‐based epoxy resin using reactive liquid rubber HTBN [hydroxy‐terminated poly(butadiene‐co‐acrylonitrile)] and TDI (tolylene diisocyanate) is described. The progress of the reaction and the structural changes during modification process are studied using IR spectroscopy, viscosity data, and chemical analysis (epoxy value determination). The studies support the proposition that TDI acts as a coupling agent between the epoxy and HTBN, forming a urethane linkage with the former and an oxazolidone ring with the latter. The chemical reactions that possibly take place during the modification ar

ISSN:0021-8995    

DOI:10.1002/app.1990.070390704

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractRefractive index and microhardness of drawn samples of poly(ethylene terephthalate) were measured by means of an Abbé refractometer and a microindentation hardness equipment. The optical and mechanical anisotropies determined from these measurements were compared with the birefringences obtained by using compensators and fitted to the affine deformation scheme, showing that microhardness anisotropy is a suitable technique for studying the overall orientation in polymers

ISSN:0021-8995    

DOI:10.1002/app.1990.070390705

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe radiation‐induced graft polymerization of 4‐vinyl pyridine to styrene–butadiene–styrene triblock copolymer (SBS) was investigated. Relations between the rate of grafting and the dose rate when SBS was irradiated in 4‐vinyl pyridine–methanol solution, and between the rate of grafting and 4‐vinyl pyridine concentration of 4‐vinyl pyridine–methanol solution have been investigated. An experiment that had been carried out on SBS immersed in various 4‐vinyl pyridine concentration of 4‐vinyl pyridine–methanol solutions showed that the extent of swelling of SBS by the various 4‐vinyl pyridine–methanol solutions increased with increasing 4‐vinyl pyridine concentration. The largest rate was found at 20 vol % 4‐vinyl pyridine–methanol solution. The rate was smaller at the volume percent of 4‐vinyl pyridine higher or lower than 20 vol %. On the assumption that the theory of homogeneous homopolymerization could be applied to this grafting reaction, the value ofkp2/ktwas obtained, wherekpandktare the propagation and termination constant, respectively. The value ofkp2/ktgreatly decreased with increasing adsorbed concentration of vinyl pyridine–methanol solution. This decrease ofkp2/ktwas explained by the fact that 4‐vinyl pyridine and methanol absorbed in SBS acted as a plasticizer which increased the molecular motion of the polymer. The solvent effect on the graft polymerization was also investigated. The result was explained by solubility parameter. When the chosen solvent had better solubility with the polymer, the degree of grafting was smaller. That was connected with t

ISSN:0021-8995    

DOI:10.1002/app.1990.070390706

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe electrical properties, such as dielectric properties and volume resistivity, of chlorinated atactic polypropylene(CAPP), obtained by thermal chlorination of APP, have been studied. The results show that dielectric constant, loss tangent, and volume resistivity of the chlorinated samples increase with the increase in degree of chlorination. The effect of CAPP as secondary plasticizer in the PVC–DOP system has also been studied. Dielectric study of PVC compounds shows a single relaxation peak, indicating no phase separation. In the case of PVC compounds, it has been observed that with the increase in CAPP content in PVC compounds dielectric constant and loss tangent decrease whereas volume resistivity increases. The increase in volume resistivity was further supported by the increase in activation energy value, obtained from volume resistivity vs. 1/Tplo

ISSN:0021-8995    

DOI:10.1002/app.1990.070390707

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe impedance characteristics of parchment‐supported inorganic precipitate model membranes have been analyzed in order to understand the mechanism of ionic diffusion through biomembranes. The observed values of membrane capacitance and resistance were found to be dependent on the concentration of bathing electrolyte and applied oscillator frequency. The change in membrane capacitance and resistance values with the change in electrolyte concentration and oscillator frequency has been interpreted in terms of changes produced in the electrical double layer at the membrane–solution interface. The values of interfacial double layer capacitance derived by the equations of Armstrong and Longer were found to be different due to the presence of polarising charge and other structural details of membrane matrix. Different model‐equivalent electrical circuits have been analyzed using the experimental data. The complex impedance spectra have been found to deviate from the theoretical predictions at low frequencies due to nonhomogenous and rough surface of the mem

ISSN:0021-8995    

DOI:10.1002/app.1990.070390708

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe synthesis of casein‐g‐poly(methyl acrylate) was studied using the potassium peroxydisulfate–ascorbic acid redox system. The effect of synthetic variables has been investigated in the light of rates of conversion of monomer, graft copolymerization and homopolymerization, percent grafting, and grafting efficiency. The results are compared with the system initiated by pure potassium peroxydisulfate

ISSN:0021-8995    

DOI:10.1002/app.1990.070390709

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractRemoval of calcium and magnesium ions in a salt solution with the macroreticular chelating resin containing aminomethylphosphonic acid groups was investigated. The resin (RMT‐P) exhibited high affinity for calcium and magnesium ions in a salt solution containing 200 g/dm3of sodium chloride. In the column method, calcium and magnesium ions in a salt solution were preferentially absorbed on the RMT‐P, when the salt solution containing 100 mg/dm3of calcium or magnesium ion was passed through the RMT‐P column at a space velocity of 15 h−1. The calcium and magnesium ions adsorbed were eluted by allowing 1 mol/dm3hydrochloric acid to pass through the column. The recycle of adsorption and elution was found to be satis

ISSN:0021-8995    

DOI:10.1002/app.1990.070390710

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY