Linear polymers with sulfur in the main chain. IV. Synthesis of thermotropic liquid‐crystalline polythioesters based on 4,4′‐biphenyldithiol with excellent adhesive properties

A series of sulfur‐containing linear polythioesters were synthesized from 4,4′‐biphenyldithiol (BPT) and bifunctionally aliphatic acyl dichlorides (ACs) by means of polycondensation. Polycondensations of BPT with azelaoyl chloride or sebacoyl chloride chosen as a model reaction system were investigated in several solvents by solution polycondensation, to find an optimal solvent to achieve high molecular weight and quantitative yield. Thus, all the polythioesters from BPT and AC (methylene number of 3–10) were synthesized in chloroform and their structures were confirmed by ¹H‐NMR and Fourier transform infrared spectrophotometer. They were also evaluated by thermogravimetry and differential scanning calorimeter (DSC). Almost all of the BPT, polythioesters exhibited two distinct exothermic and endothermic peaks on first cooling and second heating in their DSC curves, respectively. Polarized microscope (PLM) observation clarified that the higher transition temperatures were isotropic temperatures (T_is). The odd–even effect between T_i and the methylene number was observed in these BPT polythioesters. Furthermore, almost all of the polythioesters showed thermotropic liquid‐crystalline behavior, as evidenced by a PLM observation. To know the effect of introduction of sulfur on adhesive properties of the polythioester/copper junction, a single lap shear test was carried out in comparison with corresponding 4,4′‐biphenyldiol (BPH) polyesters derived from BPH and ACs. It was clarified that the BPT polythioesters have greatly higher adhesive strengths in comparison with the BPH polyesters. POLYM. ENG. SCI., 47:262–269, 2007. © 2007 Society of Plastics Engineers.