Room Temperature Sulfur Curing Agents

These curatives are useful, but they have some significant limitations. The major drawbacks are the relatively poor environmental resistance of the cured adhesives and a characteristic mercaptan odor. 

A recent example of a cationic-catalyzed room temperature cured adhesive involves the mixing of trialkoxyboroxine catalysts (27) with poly- 

While water is typically considered to be harmful to cationically curing systems, this is not always the case. Cationic dionato (from acetylacetone, acetylcyclohexanone, etc.) complexes of Si, B, Ge, and P have been prepared and studied as hydrolytically activated Bronsted acid precursors (31).  

Complex hydrolytic instability and liberated Bronsted acid strength decrease in the order of P B Si Ge for the cations and SbF AsFe PF BF4 CIO4 for the anions. Both aromatic and aliphatic epoxy resins can be used, with the aliphatic resins being the more reactive. Interestingly, the cures are only activated by the small amounts of water absorbed by a resin under ambient conditions. Addition of bulk water inhibits the resin cure, presumably by acting as a chain transfer agent. These Bronsted acid precursors can also be decomposed thermally and under UV irradiation. 

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In the one-stage vulcanization process, NR and EPDM are first masticated separately and then mixed with each other. Additives such as ZnO, stearic acid, carbon black (or silica), and process oil are added. The mix thus obtained is allowed to cool to room temperature. Finally, coupling agent known as DIPDIS and sulfur are added to the mix on the cooled mill. The stocks are finally cured under pressure at 160°C (32-33). In the two-stage process, NR and EPDM are first masticated separately. Then, additives such as ZnO, stearic acid, DIPDIS, and sulfur are incorporated in the EPDM. The compounded EPDM mix is then heated at 160°C in the hydraulic press for the predetermined time to yield the grossly undercured mix. The undercured mix is then blended with NR to the required blend ratio. The blend compound is finally vulcanized to the optimum cure time values (32-33). 

Epoxy resins based on biphenyl F have some important advantages over the bis A epoxies. Compared with bis A epoxies, bis F epoxies have a lower room-temperature viscosity a crystallization time twice as long better resistance to sulfuric acid, acetone, and methanol but at twice the price. The cured epoxy bis F is generally tougher than bis A epoxy cured with the same curing agent, but it will have a lower glass transition temperature, (Tg). 

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