Towards supramolecular side-chain liquid crystal polymers - 4. Blends of low molar mass mesogens with amorphous polymers

The thermal behaviour of blends of two low molar mass mesogens, 6-(4-methoxyazobenzene-4′-oxy)hexanoic acid, 1, and 6-(4-methoxyazobenzene-4′-oxy)hexane, 2, with polystyrene (PS), poly(4-vinyl pyridine) (P4VP) and poly(2-vinyl pyridine) (P2VP) has been characterised. 1 and 2 are enantiotropic nematogens; the clearing temperature of 1 is considerably higher than that of 2. This is attributed to the ability of 1 to form hydrogen-bonded dimeric materials. 1 is essentially immiscible with PS and thus, the transition temperatures are independent of blend composition. In contrast, a strong modification of the transition temperatures is observed on blending 1 with either P4VP or P2VP. Molecular mixing occurs in these blends below approximately 0.2 mole fraction acid. 2 is essentially immiscible with both P4VP and P2VP. The miscibility of 1 with P2VP and P4VP may be attributed therefore to the formation of hydrogen-bonded complexes. Phase separation occurs on increasing the acid concentration and this is attributed, in part, to the interaction between the mesogenic unit and the pyridyl groups. The relevance of this observation to the design of supramolecular liquid crystal polymers is discussed.