Structure and frustration in liquid crystalline polyacrylates I. Bulk behaviour

The phase behaviour and structure are reported of a new type of frustrated side-chain liquid crystalline (LC) polymer, a polyacrylate with phenylbenzoate mesogenic side groups and a narrow polydispersity. At a high degree of polymerisation the LC polymers show a nematic, a smectic-A_d, a re-entrant nematic and a C phase, for shorter chains only a nematic and a C phase. This constitutes a new example of nematic re-entrance for which the driving field is the length of the polymer chain. The smectic-A_d layers consist of partially overlapped side groups while in the C phase the side chains are rearranged into chevron-like blocks of bilayers. We propose an explanation of the frustrated phase behaviour in terms of these two different competing length scales and their coupling to the backbone conformations. Received 28 February 2001 and Received in final form 6 August 2001