UBC Theses and Dissertations
Ab initio studies of novel polymer cross-linkers Pei, Zhipeng
A polymer cross-linker is a chemical agent that can create covalent bonds between the molecular chains that comprise a polymeric material. Recently, a novel, versatile, bis-diazirine based polymer cross-linker was reported,1 but its cross-linking efficacy is relatively low and can be improved. Moreover, the details of the mechanism of cross-linking has not been reported. In this thesis, we use state-of-art computational chemistry methods to explore how carbenes derived from bis-diazirines engage in cross-linking and identify the factors that affect the cross-linking efficacy. The computational results show that bis-diazirines do not form bis-carbenes in a concerted fashion upon thermal activation. Instead, the carbene centers are generated sequentially. The use of substituents on the carbene center (i.e. p-X-C6H4-C̈-R) and para to the carbene center can significantly influence the electronic state of carbenes, as well as the barrier heights associated with carbene formation and carbene insertion. Therefore, substitution provides a general strategy to control the reactivity of the cross-linker. We also explore how tether units and different ring structures may impact cross-linker performance, and possible carbene side- and self-reactions. To the best of our knowledge, this is the first computational study on this type of polymer cross-linker, and the results provide guidance and insights for improving cross-linking performance systematically. The data obtained were used to propose a next-generation diazirine-based polymer cross-linker.
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