Synthesis And Properties Of Linear Polyesters Containing 1,3,4-oxadiazole And Azobenzene Unit

In this paper, a new compound 5-[4-(hexadecane alkoxy) phenylazo]-1,3-benzene-bis(2-1,3,4-oxadiazole) thiophenols (7) is synthesized by nitrification, esterifation, reduction, diazotization, alkylation, ammoniation, cyclization with 1,3-benzenedicarboxylic acid as raw material. Three new linear polyesters(P1～P3) containing azobenzene and 1,3,4-oxadiazole units are synthesized by condensation polymerization with 5-[4-(hexadecane alkoxy) phenylazo]-1,3-benzene-bis(2-sulfide-1,3,4-oxadiazole) methyl acetate (8) which is synthesized by substitution with compound 7 as starting material and different glycols (ethylene glycol,1,3-propylene glycol,1,6-hexylene glycol). The structure of the intermediates and polyesters(P1～P3) are confirmed by IR, UV-vis and 1H NMR. The intrinsic viscosities of polyesters(P1～P3) in tetrahydrofuran are 0.3213 dL/g(Pl),0.4107 dL/g(P2), 0.5613 dL/g(P3). The Mn are 6584 g/mol(P1),7499 g/mol(P2),7562 g/mol(P3). The Mw are 9548 g/mol(P1),11774 g/mol(P2),12554 g/mol(P3). PDI are 1.45(P1),1.57 (P2), 1.66(P3).The thermal stability of the polyesters(P1～P3) are characterized by TG, the 5% weight loss temperature of P1～P3 are 239℃,245℃,264℃.Polyesters(P1～P3) with azobenzene and oxadiazole unit are solubled in common organic solvents such as tetrahydrofuran and chloroform, which display well solubility. The monomers and polyesters(P1～P3) take place trans-cis photoisomerization under the radiation of 365 nm UV light. The efficiency of trans-cis photoisomerization(R), the content of cis-isomer(Y) and the rate constant of photoisomerization (kp) of monomers and the polyesters(P1～P3) are calculated, R are 83.14%(6),80.95%(8),76.33%(P1),75.20%(P2),74.17%(P3); Y are 87.34%(6),84.99%(8),80.15%(P1),78.97%(P2),77.88%(P3); kp are 0.7613 min-1(6), 1.3389 min-1(8),1.1881 min-1(P1),1.2081 min-1(P2),1.1790 min-1 (P3). The R, Y and kp of monomers are greater than the polyesters(P1～P3), which is attributed to the increased steric hindrance in polymer and the trans-cis photoisomerization of azobenzene is limited.The emission peak of the polyesters have a broad peak, which is azobenzene and oxadiazole structures. The results indicated that the polymers emitted purplish blue fluorescence at 402 nm. The polyesters (P1～P3) with azobenzene and oxadiazole unit show excellcent solubility, good thermal stability, trans-cis photoisomerzation property and fluorescence property, which can be used in the field of optical functional polymer materials.