A series of supramolecular networks and polymers created through competitive hydrogen bonding of a pair of bis-benzoic acid hydrogen bond donors and a mixture of hydrogen bond acceptors: a series of liquid crystal-forming flexible bi-pyridyl species and polyfunctional (tetra, tri and bi) pyridyl-containing species. The associative chain structures displayed mesogenic characteristics at loadings dependant on the flexibility of the ethylenglycoxy chains and the functionality of the crosslinking agents. 4EOBBA/3EOBSB/2PD complexes lost liquid crystallinity at 17.5% loading. The same acid and mesogenic acceptor when crosslinked with 3PD eliminated liquid crystallinity at 20%, while four-fold networks utilizing 4PD lost mesogenicity at 22.5%. When the more flexible 5EOBBA hydrogen bond donor was used and 5EOBSB acceptor were used, networks and random copolymers formed displayed higher loadings of crosslinking agent: 22.5% for the 4PD- containing species, 30% for 3PD and 35% for 4PD.  It is supposed that the decreasing loading concentrations are a function of decreasing melting temperatures of the crosslinking agent. It is supposed that this increased tolerance for disruptive agents can be attributed to the flexibility possessed in the bis-acid molecule reported here. The increased flexibility allows for the chains to realign and maintain mesogenicity by overcoming localized structural defects and disruptive agents. While this observation may be unique to supramolecular liquid crystalline macromolecules (with the ability to form/break hydrogen bond associations), this general trend is in keeping with previous works involving main-chain and side chain liquid crystalline polymers.

Supramolecular main-chain liquid crystalline polymers and networks with competitive hydrogen bonding: A study of flexible bis-acids and a mixture of flexible mesogenic bispyridyls and flexible polypyridyls

243rd National Meeting (2012)

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