Crosslinking epoxy resin

L. Mascia and T. Tang, Ceramers based on crosslinked epoxy resins-silica hybrids low surface energy systems, J. Sol-Gel Sci. Technol., 1998, 13, 405. 

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. 

In our initial studies ( ), we examined several series of cured resins using ortho and meta isomers of phenylene diamine. p-Phenylenediamlne weis not considered for stu< due to its known ceurclnog lc nature. As shown in Table I, o-phenylenediamine (OPD) used edone was found to impart inferior properties to the crosslinked epoxy resin. We subject the poor performance of OPD is attributable to intramolecular hydrogai bonding, as shown below ... 

Both anionic and cationic initiation are used to cure (polymerize and crosslink) epoxy resins (Sec. 2-12d) by ROP of the oxirane end groups. Photochemical cationic initiation (Sec. 5-2a-4) is important in various coating applications (3-4c) [Decker et al., 2001]. 

For polystyrene and related thermoplastic copolymers, this inherent brittleness has been corrected effectively by including rubbery particles, properly modified by grafting with thermoplastic chains, for energy dissipation (6). With crosslinked epoxy resins, chemical attachment of the... 

The use of the above equations is shown in Fig. 25 where the calculated and measured [45] Young s modulus of a crosslinked epoxy resin filled with silica (Si02) particles are compared. The elastic properties of the filler and matrix are [44]... 

Siebert and Riew (4) described the chemistry of the in situ particle formation. They proposed that the composition of the particle is a mixture of linear CTBN-epoxy copolymers and crosslinked epoxy resin. The polymer morphology of the CTBN toughened epoxy systems was investigated by Rowe (5) using transmission electron microscopy by carbon replication of fracture surfaces. Riew and Smith (6) supported the... 

The second type of reaction concerns the use of hydroxymethyl or, more frequently, alkoxymethyl derivatives of melamine, that is, a multifunctional amine, in aminomcthylation (or transaminomethylation) reactions. Crosslinked epoxy resins are also obtained by reaction with epoxides (Fig. 188). - -... 

The inclusion of an overall reaction order parameter greatly increases the correlation of the predicted and experimental viscosity profiles for highly crosslinked epoxy resin systems. 

Finally, it is highly desirable to improve the ability to calculate the properties of surfaces and interfaces involving polymers by means of fully atomistic simulations. Such simulations can, potentially, account for much finer details of the chemical structure of a surface than can be expected from simulations on a coarser scale. It is, currently, difficult to obtain quantitatively accurate surface tensions and interfacial tensions for polymers (perhaps with the exception of flexible, saturated hydrocarbon polymers) from atomistic simulations, because of the limitations on the accessible time and length scales [49-51]. It is already possible, however, to obtain very useful qualitative insights as well as predictions of relative trends for problems as complex as the strength and the molecular mechanisms of adhesion of crosslinked epoxy resins [52], Gradual improvements towards quantitative accuracy can also be anticipated in the future. 

Table 7.5 Results of Tg-value calculations on crosslinked epoxy resin systems...

Pigure 12. Thermal expansion behavior of fully-crosslinked epoxy resins as a function of sub-T annealing time at 140 0. 

Many different aliphatic and aromatic polyamines are available for crosslinking epoxy resins. Some of these are ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepen-... 

Many cyclic acid anhydrides are used industrially for crosslinking epoxy resins. These are mono-and polyanhydrides. Some typical, conunercially used anhydrides are shown. 

Ester and ketone solvents, which react with amines, must not be present. The adduct is a polyamine and can therefore be used to crosslink epoxy resins. It has advantages in that it is odourless (simple amines are unpleasant to handle), part-reacted (which speeds up drying) and free from simple amines (which cause exudation). It can be seen now why it is an advantage to age paints cured by simple amines amine adducts are formed during the ageing. 

A typical example of recent studies of time-temperature-modulus relationships may be found in papers by Moehlenpah et al. (1970, 1971), who examined crosslinked epoxy resins filled with glass beads, fibers, or air bubbles. The initial tangent modulus in compression was seen to increase with a decrease in strain rate flexural and tensile moduli were reported to behave in a similar fashion. The WLF shift factor was essentially independent of the type of filler used and of the mode of loading. Kerner s equation was found to hold for the particulate composites in the glassy range. 

A highly crosslinked epoxy resin was modified by reactive blending with bisphenol Apolycarbonate. The bisphenol A polycarbonate was dissolved at high temperature in the uncured epoxy resin before the curing process. The physical and chemical interactions between the two components were studied by IR. Isothermal measurements showed that the presence of polycarbonate did not affect the overall curing mechanism but decreased both the initial reaction rate and the final conversion of reactants (278). 

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