Supramolecular main-chain liquid crystalline polymers and networks with competitive hydrogen bonding: flexible bis-cinnamic acids as hydrogen bond donors in thermoreversible networks and polymers

Abstract

A series of novel liquid crystalline supramolecular networks formed through competitive hydrogen bonding has been synthesised. These networks are composed of a flexible bis-cinnamic acid and two types of pyridyl species – a small rigid bipyridyl capable of forming liquid crystalline phases and polyfunctional non-mesogenic pyridyl species capable of forming thermoreversible networks. It was found that the networks display a monotropic nematic character at relatively high concentrations of disrupting netpoints – up to 30% for tetrapyridyls, 25% for tripyridyls and 15% for bipyridyls. Very strong crystallisation enthalpies occurred almost immediately after the formation of mesophases, in some cases masking the liquid crystalline phase during thermal analysis. It is believed that the increased mesogen length and rigidity is inducing crystallisation from the mesophase. Completely networked systems – containing no rigid bis-pyridyl – formed glassy materials with no anisotropy.