AROMATIC COPOLYESTERS WITH STILBENE MESOGENIC GROUPS .1. LIQUID-CRYSTALLINE PROPERTIES OF COMPOUNDS CONTAINING A STILBENE, TEREPHTHALOYL, OR HYDROQUINONE CENTRAL GROUP

Model compounds (S(n)) of stilbene-unit containing copolymers are stud ied and compared with compounds T(n) and H(n) derived from terephthali c acid and hydroquinone, respectively. They have the following structu res: Ar[COOC6H4COO(CH2)nCH3]2, where Ar = -C6H4CH=CHC6H4- (S(n)) and A r = -C6H4- (T(n)); Ar[OOCC6H4COO(CH2)nCH3]2, where Ar = -C6H4- (H(n)). Their liquid crystalline behaviors are established by DSC, optical mi croscopy, and X-ray diffraction. The lower homologues in the T(n) and H(n) series show only a nematic phase. When the alkyl group is lengthe ned, both nematic and S(A) phases are formed. In the higher homologues purely S(A) behavior is observed, with compound H7 exhibiting a monot ropic S(C) phase. All the S(n) compounds studied give N and S(C) phase s, with compounds S2, S3, and S6 exhibiting a S(C)-S(A) transition. Th e effects of the central unit of the mesogenic group on liquid crystal properties are illustrated by reference to compounds T(n), H(n), S(n) , and N(n) (containing a 2,6-disubstituted naphthalene central ring). The effects of relatively small structural changes are illustrated by reference to compounds in which the n-alkyl chains are connected to th e mesogenic groups by ester (T(n), H(n)), ether (T(on), H(on)), and di rect (T(dn), H(dn)) linkages.