Epoxy-aromatic diamine systems

Liu, H. Uhlherr, A. Varley, R.J. Bannister, M.K. (2004). Influence of substituents on the kinetics of epoxy/aromatic diamine resin systems. Journal of Polymer Science Part A Polymer Chemistry, Vol.42, No.l3, (July 2004), pp. 3143-3156, ISSN 1099-0518. 

In addition to electrical uses, epoxy casting resins are utilized in the manufacture of tools, ie, contact and match molds, stretch blocks, vacuum-forrning tools, and foundry patterns, as weU as bench tops and kitchen sinks. Systems consist of a gel-coat formulation designed to form a thin coating over the pattern which provides a perfect reproduction of the pattern detail. This is backed by a heavily filled epoxy system which also incorporates fiber reinforcements to give the tool its strength. For moderate temperature service, a Hquid bisphenol A epoxy resin with an aHphatic amine is used. For higher temperature service, a modified system based on an epoxy phenol novolak and an aromatic diamine hardener may be used. 

Other latent curing agents that are used in solid adhesives are dihydrazides and BF3-MEA complexes. These compositions are also stable at room temperature but cure when heated. Solid anhydrides can be used in one-component powder blends (e.g., 10 pph of trimellitic anhydride accelerated with 0.5 pph of 2-methylimidazole). Solid systems with aromatic diamines are prepared by comelting the solid epoxy with the amine. Typically 30 pph of curing agent is used.1... 

Covers a two-part epoxy-resin system in the form of a bisphenol "A" epoxy resin filled with fumed silica and carbon microspheres and a separate aromatic diamine curing agent. 

A linear-chained epoxy resin was formulated from phenyl glycidyl ether and nadic methyl anhydride, catalysed by benzyldimethylamine (248). An IR fibre-optic probe was used to follow the conversion of a thermosetting tetrafunctional epoxy resin in which the hardener was an aromatic diamine and a carboxylic dianhydride. A polymerisation system consisting of a cycloaliphatic diepoxide, epoxidised natural rubber (ENR), glycidyl methacrylate (GMA) and a cationic photoinitiator, triphenylsulfonium hexafluoro-antimonate, was studied (75). Multifunctional epoxy/ amine formulations (Epon 825 plus 4,4 -methylene-... 

The required temperature resistance depends on the application conditions. For the lower temperature regions, the classical systems based on diglycidyl ether of Bisphenol A (DGEBA) cured with aromatic diamines like 4,4 -diaminodiphenylmethane (DDM) or 4,4 -diaminodiphenylsulphone (DDS) and systems containing dicyandiamide have been used. To increase the bond density and the temperature resistance, polyfunctional epoxy resins have been introduced.(N,N,N, N -tetraglycidyl-4,4 -diaminodiphenylmethane (TGDDM) is an example.) The glass transition temperature, Tg, of these systems may increase far above 200 C. 

Attempts have been made to overcome some of the drawbacks of 10-cured epoxy systems by synthesizing and evaluating structurally similar species as replacements. Aromatic cyanimides, prepared from aromatic diamines and cyanogen chloride, have been evaluated as replacements for 10 with the hope that they would be soluble in epoxy resins (Eq. 21... 

Babayevs, P.G. and Gdlham, J.K. (1973) Epoxy thermosetting systems — dynamic mechanical analysis of reactions of aromatic diamines with diglyddyl ether of bisphenol-A./. Appl. Polym. Sci., 17 (7), 2067-2088. 

Grillet, A.C., Galy,)., and Pascault, J.P. (1992) Influence of a 2-step process and of different cure schedules on the generated morphology of a rubber-modifled epoxy system based on aromatic diamines. Polymer, 33 (1), 34-43. 

A very convenient system for performing this investigation consists of epoxy networks formed by reacting aromatic epoxy on aliphatic diamine. Indeed, the different nature (aromatic or aliphatic) of the units allows one to apply 13 C NMR for identifying the groups involved in the transitions and their motions. Furthermore, in the same way as for polyethylene tere-phthalate), specific small molecule additives act as antiplasticisers, which can offer an additional possibility for investigation of the molecular motions and their cooperativity. 

In the case of epoxy networks with a secondary diamine, like DMHMDA, the network architecture is such that flexible aliphatic sequences are present as chain extenders between the crosslink points. In such architectures, the motions of the HPE units can develop towards other HPE sequences (either along the chain or spatially neighbouring) without involving the crosslink points in their cooperativity. Thus, with these systems a different nature of cooperativity exists compared to the other network architectures. The introduction of an antiplasticiser in such a local packing does not affect the cooperativity as much as with the densely crosslinked architecture, for the crosslinks are not so much involved. Once more, it is important to point out that the flexible nature of the aliphatic amines does not matter since the same behaviours are observed for fully aromatic systems with identical architecture [68]. 

Epoxy adhesives are generally more resistant to a wide variety of liquid environments than other structural adhesives. However, the resistance to a specific environment is greatly dependent on the type of epoxy curing agent used. Aromatic amine (e.g., metaphenylene diamine) cured systems are frequently preferred for long-term chemical resistance. 

Fig. 9a and b. TBA spectra for a series of isothermal cures showing changes in (a) the relative rigidity and (b) the logarithmic decrement vs. time. Gelation and vitrification are evident in the 80, 125 and 150 °C scans, but only vitrification is observed in the 200 and 250 °C scans. The system studied was a trifunctional epoxy resin, XD7342 [triglycidyl ether of tris(hydroxyphenyl)-methane, Dow Chemical Co.], cured with a tetrafunctional aromatic amine, DDS (diamin iphenyl sulfone, Aldrich Chemical Co.)... 

Combined tertiary/secondary amine curatives, prepared from ter-tiary/primary diamines and epoxy resins, have been used as accelerators for primary aromatic amine cures of DGEBA-type epoxy resins. For example, diethylaminopropylamine/DGEBA resin adducts have been used in m-phenylenediamine-cured epoxy resin systems to provide relatively low temperature cures (50-160°C). The cured resin systems have good toughness and heat distortion temperatures near 130°C. 

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