LIQUID-CRYSTALLINE PHASE-TRANSITIONS OF THE '-ALKOXYBIPHENYL-4-YL)-5-(4-METHYLPHENYL)PYRIDINES

The mesomorphic phase transitions have been studied for a series of 4' -alkoxybipheny1-4-yl)5-(4-methylphenyl)pyridines (4R-Pn; the carbon nu mber, n, of the alkoxy group is 1-10) by use of DSC and polarizing opt ical microscopy. The 4R-Pn compounds showed only a nematic phase for n = 1 and 2, but underwent characteristic polymesomorphic sequences whe n n greater than or equal to 3; Cr reversible arrow CrH reversible arr ow SmF reversible arrow SmC reversible arrow SmA reversible arrow N re versible arrow I with n = 3 and 4, and Cr reversible arrow CrH reversi ble arrow SmF reversible arrow SmA reversible arrow N reversible arrow I with n = 5-10. This mesomorphic phase transition behaviour was simi lar to that of the 2-(4-alkoxyphenyl)-5-(4-methylphenyl)pyridine (3R-P n) series reported previously and it is proposed that the 4R-Pn and 3R -Pn compounds have a minimum terminal alkoxy length (critical alkoxy l ength) for the generation of LC polymorphism.