Side chain liquid crystal copolymers containing electron rich and electron deficient mesogenic groups. The synthesis and characterization of the poly[ω-(4-cyanobiphenyl-4′-oxy)alkyl methacrylate]s-co-poly[6-(4-butylazobenzene-4′-oxy)hexyl methacrylate]s

The synthesis and characterization of a new series of side chain liquid crystal copolymers, the poly[ω-(4-cyanobiphenyl-4′-oxy)alkyl methacrylate]s-co-poly[6-(4-butylazobenzene-4′-oxy)hexyl methacrylate]s, is described. These copolymers contain electron rich 4-butylazobenzene-based mesogenic groups and electron deficient 4-cyanobiphenyl units. The spacer attached to the electron rich units is held at 6 methylene units while that attached to the 4-cyanobiphenyl groups is varied in length from 3 to 12 methylene units. All the copolymers exhibit a smectic A phase and, in addition, the homologues containing a pentyl spacer or spacer lengths ≥7 methylene units exhibit either a crystal B or smectic B phase. The clearing temperatures of the copolymers are significantly greater than the average values for the corresponding homopolymers. This behaviour is interpreted in terms of a favourable specific interaction between the unlike groups in the copolymer. By comparison, the clearing entropies exhibited by the copolymers are lower than the average values of the corresponding homopolymers and it is suggested that this reflects a disruption of the efficient packing of the 4-butylazobenzene groups by the 4-cyanobiphenyl units. The sole exception to this is the copolymer containing a pentyl spacer for which the clearing entropy is greater than the average value for the homopolymers; this copolymer also exhibits the largest deviation in the clearing temperature. This strongly suggests that the specific interaction is maximized for this particular combination of spacer lengths.