CHIRAL SMECTIC LIQUID-CRYSTALLINE POLYACRYLATES WITH VARIOUSLY SPACED AND SUBSTITUTED BIPHENYLENE UNITS

Four new classes of chiral liquid-crystalline polyacrylates A-n to D-n based on variously spaced and substituted biphenylene mesogens have been prepared. Spacer segments of n (= 5-11) methylene groups were used, and the chiral substituents were the (S)-2-methylbutoxy (A-n), (S)-l-methylheptyloxy (B-n), (S)-2-chloro-3-methylbutanoyloxy (C-n), or (2S,3S)-2-chloro-3-methylpentanoyloxy (D-n) groups. The polyacrylates exhibited a strong tendency to form the smectic A mesophase, sometimes in polymorphic sequences. In particular, on varying the length of the alkylene spacer of polyacrylates A-n the structure of the chiral smectic A phase evolved from bilayer (n less-than-or-equal-to 6) to interdigitated (n=7) and to monolayer (n>7). Depending on the nature of the chiral substituent, chiral smectic C and chiral nematic mesophases were also observed in a few samples. The polyacrylates appeared to be suitable candidates for studies of the electroclinic response in the chiral smectic A phase.