LIQUID-CRYSTALLINE POLYETHERS BASED ON CONFORMATIONAL ISOMERISM .18. POLYETHERS BASED ON A COMBINED MESOGENIC UNIT CONTAINING RIGID AND FLEXIBLE GROUPS - 1-(4-HYDROXY-4'-BIPHENYL)-2-(4-HYDROXYPHENYL)BUTANE

The synthesis of the racemic mesogenic unit 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)-butane (TPB) which represents a combination based on rigid and flexible groups is presented. The "polyethers" based on TPB and alpha,omega-dibromoalkanes (TPB-X) containing from 4 to 20 methylenic units (X) were synthesized by phase-transfer-catalyzed polyetherification and characterized by a combination of differential scanning calorimetry and thermal optical polarized microscopy. All polymers are soluble in conventional solvents at room temperature. TPB-X polyethers are copolymers containing four different constitutional isomeric structural units derived from the two enantiomers of TPB. TPB-5 is glassy. TPB-4 to TPB-10 exhibit only an enantiotropic nematic mesophase. TPB-11 to TPB-15 and TPB-17 exhibit a crystalline and an enantiotropic nematic mesophase and TPB-16 a crystalline phase and a monotropic nematic mesophase, while TPB-18 to TPB-20 are only crystalline. The phase behavior of TPB-X was explained by analyzing the various trends of the dependences of the glass transition, nematic-isotropic, isotropic-nematic, melting, and crystallization temperatures as a function of X.