Study of Structure-property Relationships of Poly(benzobisthiazole) and it’s Derivatives

Abstract

Poly(p-phenylene benzobisthiazole) (PBZT) and a series of new derivatives, poly(benzobisthiazole-1,4-diphenylene etherylene) (PBTPE), poly(bisbenzothiazole-2,2’-phenelyene-6,6’-(4-tert-butyl)cyclohexylidene) (PBTPBCH) and poly(bisbenzothiazole-2,2’-phenelyene etherylene-6,6’-(4-tert-butyl)cyclohexylidene) (PBTPEBCH), were synthesized by polycondensation of 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT·2HCl) or 1,1-bis(4-amino-3-mercaptophenyl)-4-tert-butylcyclohexane dihydrochloride (BAMPBCH·2HCl) with terephthalic acid or 4,4’-dicarboxydiphenyl ether in poly (phosphoric acid) (PPA). The inherent viscosity, thermal stability, solubility, morphology and photophysical properties of them were investigated and compared in detail. The introduction of etherylene or 4-tert-butylcyclohexylidene both decreased the inherent viscosity of PBZT. Although the decomposition temperatures of these derivatives were lower than PBZT, they still had good thermal stability. In addition, the thermogravimetric analysis showed PBTPBCH and PBTPEBCH containing 4-tert-butylcyclohexylidene had the lower thermal stability than PBTPE containing etherylene. The solubility of them was all enhanced. Especially, PBTPBCH and PBTPEBCH showed better solubility. X-ray diffractograms of all the derivatives showed that they were amorphous. Compared with PBZT, the absorption maximum (λmax) of all the derivatives prepared was blue shifted in different degree according to their structure respectively. The excitation and emission peaks were also blue shifted. Furthermore, both of the substituting groups incorporated into the polymer backbone could improve the photoluminescence quantum yield to a certain extent. Finally we established the structure-property relationships of this class of poly(benzothiazole)s by investigating and comparing these properties in detail.