Cross-linking effect after operation

The major benefit with this approach is that some degree of toughness can be given to inherently brittle cured epoxy matrices designed to operate at service temperatures above about 135 to 150°C, that is, highly cross-linked adhesives. Further, as most of the thermoplastics used also have TgS at these levels or considerably above, should some polymer remain in the continuous phase after cure, the effect on the final thermal properties will not be as deleterious as with RLP or elastomeric toughening. 

A closer look at the system, however, does pique curiosity. The initial pH within the chamber is not 7 but 2-3, and the reactions are non-equilibrium, often irreversible, and involve other intermediates that can become important end products. The acidic pH represents a problem in that thiolates, not thiols, are the operative reductants, thus cannot reduce at pH values below their typical i.e. 8-9. This is resolved by proteins, including mfp-6, by sequence specific effects such as flanking cationic groups that reduce the Cys pK, e.g. redox active Cys-59 in DsB-A has a p Tg of 3.5. Several Cys residues in mfp-6 are acidic, but specific p Tg values have yet to be measured. The non-equilibrium, irreversible nature of the oxidation reactions is a particular problem with Dopa and other catechols. Indeed, the chemical fate of catechols in mussel byssus is highly dependent on their location. In the cuticle, the fate of Dopa appears to be tris catecholato-Fe complexes in the thread and plaque core, Dopa forms covalent cross-links after oxidation to quinones, whereas at the plaque-substratum interface, it is some combination of metal chelates and reduced H-bonded Dopa on metal oxide surfaces. The reducing capacity of mfp-6 plays a role in maximizing the latter and is astonishingly sustained, i.e. >21 days. ... 

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