Acceptor monomers interaction with Lewis acids

If the nucleophilicity of the anion is decreased, then an increase of its stability proceeds the excessive olefine can compete with the anion as a donor for the carbenium ion, and therefore the formation of chain molecules can be induced. The increase of stability named above is made possible by specific interactions with the solvent as well as complex formations with a suitable acceptor 112). Especially suitable acceptors are Lewis acids. These acids have a double function during cationic polymerizations in an environment which is not entirely water-free. They react with the remaining water to build a complex acid, which due to its increased acidity can form the important first monomer cation by protonation of the monomer. The Lewis acids stabilize the strong nucleophilic anion OH by forming the complex anion (MtXn(OH))- so that the chain propagation dominates rather than the chain termination. 

The study of the interaction mechanism of thin films of BACY prepolymer on different surface states of Si and oxidized Al employing advanced techniques such as XPS, UPS, MIES, IR reflection spectroscopy, and AFM was undertaken by Possart and Dieckhoff [364]. The trioxy triazine was the only moiety identified to have adhesive interaction with the substrate. On a Si surface, the mechanism was identified as donor-acceptor interaction where the lone pairs of electrons on N and O atoms of trioxy triazine were involved in the electron donor process for the Si cation. On aluminum oxide, the Lewis acidic OH groups act as electron acceptors, withdrawing electron density from the lone pairs of O and N of the trioxy triazine. Back donation of electron density from Al metal to the organic layer is operative beneath the oxide layer. The dicyanate monomer doesn t adhere at all and desorbs quickly out of the interphase region on the substrate. It was concluded that thermosetting reaction of the prepolymer is thus hampered and the resulting network will be less dense near the substrate than in the bulk. 

Two classes of acceptor substituents have been studied for the possibility of stabilizing N(, substituents with vacant u-orbitals, but with no electron pairs capable of interacting with the n-system (i.e. H, Lewis acids), and substituents with both vacant u-orbitals and potentially interacting 7t-systems (i.e. carbenes and nitrenes). The former class destabilize the ring, rendering the three separate monomers (e.g. more stable the latter stabilize the ring relative to the separate... 

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