Curing mechanisms with anhydride

Different behaviors and mechanisms were clearly recognized between these resins. Epoxy resin cured with amine showed no degradation during immersion because of its stable crosslinks. Epoxy resin cured with anhydride showed the uniform corrosion with the softening and dissolution of the surface and also behaved similar to the oxidation corrosion of the metal at high temperature obeying linear law. 

It is evident that relaxation studies in the solid state can look at the motions which are responsible for the mechanical properties of the cured epoxy systems 43). Therefore, Garroway, Moniz and Resing continued to do relaxation studies 61). Garroway, et al. looked at four epoxy polymers based on the DGEBA resin. Two of the epoxy resins were cured with amines and the other two were cured with anhydrides. Proton enhanced spectra of the epoxy systems were generated. The solid state spectra were compared to the solution spectra of the unreacted epoxy. The< epoxy resin of interest was again DGEBA which was reacted with ... 

Kannebley 30) and Sorokin et al. 31,32) obtained second-order rate constants for the relevant model bimolecular reactions whereas Arnold 19) and Doszlop et al.37) consider curing of epoxy resin with anhydride or reactions of monoepoxides with various proton-donor compounds to be first order (Table 1). Considering the mechanism of individual reactions which proceed during curing or in the non-catalyzed... 

The present study, by contrast, deals with toughening of cycloaliphatic type epoxies with anhydride curing agents normally used in industrial applications. In addition to developing mechanical property data, the morphological characteristics were also studied. 

The anhydrides are sometimes used alone, but more frequently in combination with such basic compounds as tertiary amine catalysts. The suggested curing mechanism is roughly as follows 14 16) ... 

Curing with anhydride hardeners requires a long curing time and a high temperature. The cured resins are excellent in mechanical and particularly in electrical properties at temperatures above Tg. Anhydride hardeners are extensively used. Many practical studies on mechanical and electrical properties 381 but few systematic studies on the structures of the cured resins and physical properties have been reported 27,39 41). The reasons why such systematic studies are scarce are as follows Most of the acid anhydride hardeners are cyclic anhydrides of dibasic acids. The main structure of the cured resins is such as shown in Fig. 1 b. Differences among the structure of the cured resins with different hardeners are only based on the differences in the R segment and consequently, cured resins with rather different mechanical properties cannot... 

CEs are known to react with phenols to form iminocarbonates which eventually lead to polycyanurates with the liberation of more acidic phenol moiety. This can be a method to alter the gel point of the resin, Tg, and thermal stability of the network by co-curing diphenol with CE. Thus, copolymerization of dicyanate with diphenols resulted in polycyanurates with altered network structure and diminished crosslink density [237]. However, an earlier report claims poly(imi-nocarbonate) by reaction of these two in equimolar quantities. The thermoplastic so formed was reported to retain the mechanical properties like a polycarbonate. This approach can produce strong, non-toxic, biodegradable films and molded plastics that are degradable at temperatures above 140 °C [169,238]. Except for a few very early reports [239], the reaction of CE with anhydrides to form poly(iminocarbamates) has not been explored much. 

AY 180-220 < 1 organics or 2-4 caprolactam 70-100 moderate mechanical properties, very good hardness and outstanding weather resistance, in the case of PUR hardening layer thickness limited due to caprolactam release AY cured with anhydride adducts forms very smooth films and can be cured at temperatures down to I40 C... 

Figure 3.4 Anhydride-curing mechanism for epoxies (a) reaction of hydroxyl group (from epoxy resin) with anhydride (b) reaction of carboxylic acid group with epoxy (c) reaction of...

The curing mechanism of an epoxy resin with an anhydride involves a number of reactions taking place simultaneously. The principal reactions are ... 

The mechanism of anhydride cure is complex and controversial because of the possibility of several competing reactions. The imcatalyzed reaction of epoxy resins with acid anhydrides proceeds slowly even at 200°C both esterification and etherification occur. Secondary alcohols from the epoxy backbone react with the anhydride to give a half ester, which in turn reacts with an epoxy group to give the diester. A competing reaction is etherification of an epoxy with a secondary alcohol, either on the resin backbone or that formed during the esterification, resulting in a -hydroxy ether. It has been reported that etherification is a probable reaction since only 0.85 eqiuvalents of anhydrides are required to obtain optimiun cross-linked density and cured properties (103). 

The following mechanism is consistent with the experimental data described in the literature [82,83] for the cure of epoxy resins with anhydrides in the presence of tertiary amines. In the first step, an activation of anhydride by the amine takes place ... 

Samper, M.D., Fombuena, V., Boronat, T., Garcia-Sanoguera, D., Balart, R., 2012. Thermal and mechanical characterization of epoxy resins (FLO and ESO) cured with anhydrides. J. Am. Oil Chem. Soc. 89, 1521-1528. 

An important appHcation is for filament-wound glass-reinforced pipe used in oil fields, chemical plants, water distribution, and as electrical conduits. Low viscosity Hquid systems having good mechanical properties (elongation at break) when cured are preferred. These are usually cured with Hquid anhydride or aromatic-amine hardeners. Similar systems are used for filament-win ding pressure botdes and rocket motor casings. 

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