Thiophene- and silarylene-containing polyesters. Resonance effect on conductivity after polarization in an external electric field

• Published in: Polymer international 2012-05, Vol.61 (5), p.810-817
• Main Authors: González-Henríquez, Carmen M, Tagle, Luis H, Terraza, Claudio A, Leiva, Ángel, Barriga González, Andrés, Volkmann, Ulrich G, Cabrera, Alejandro L, Ramos-Moore, Esteban, Pavez-Moreno, Maximiliano
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensing; conducting polymers; conjugated polymers; Electric fields; Electrical resistivity; Energy gaps (solid state); Exact sciences and technology; Infrared; optical and thermal properties; Physicochemistry of polymers; Polyester resins; Polymer industry, paints, wood; Resistivity; Semi-solid processing; Technology of polymers; X-rays
• ISSN: 0959-8103; 1097-0126
• DOI: 10.1002/pi.4147

Polyesters were synthesized by direct polycondensation of thiophene‐2,5‐dicarboxylic acid and five different silarylene‐containing diphenols using a tosyl chloride/pyridine/N,N‐dimethylformamide system as a condensing agent. Polymers were obtained in good yields and were characterized using Fourier transform infrared and NMR (1H, 13C, 135‐DEPT and 29Si) spectroscopy and elemental analysis. All polymers were completely soluble in aprotic organic polar solvents such as dimethylformamide, dimethylsulfoxide and N‐methyl‐2‐pyrrolidone. The range of effective mass of the polymers (m/z) was 1 × 105–2 × 105, determined using electrospray ionization mass spectrometry. Asymmetry and steric hindrance prevented dense packing of the polymeric chains, showing glass transition temperatures between − 78 and − 51 °C and loss of thermal stability at 177–199 °C (10% weight loss). Additionally, the melting points of the polyesters were found to be in the range 62–67 °C. Because of this, the samples were semi‐solid at room temperature. The optical band gaps of the polymers were observed between 4.54 and 4.48 eV, corresponding in all cases to insulator behavior. The molecular structure of the samples was studied using X‐ray diffraction, showing a degree of order that was associated with two monoclinic lattices. Additionally, the conductivity was studied using a two‐point method with contacts on top of polymer films. Prior to the electrical measurement, the samples were polarized in an external electric field of 0.8 to 6.4 V cm−1, and the alignment of the dipoles increased the electrical conductivity. Copyright © 2012 Society of Chemical Industry Polyesters containing silarylene and thiophene units were synthesized. The resonance effect on conductivity after polarization by application of an external electric field was studied. According to the results, the polymers are dielectric insulators, where the chains can be broken above a threshold field, properties that are associated with a high band gap.