Enzymatic synthesis of water‐soluble conducting poly(3,4‐ethylenedioxythiophene): A simple enzyme immobilization strategy for recycling and reusing

Abstract

The field of intrinsically conducting polymers has attracted high attention due to their interesting electrical and optical properties. Since their discovery in 1977, they have been investigated for many technological applications, such as organic lightweight batteries, microelectronics, optical displays, antistatic coatings, sensors, direct metallization, all-polymer actuators, and electromagnetic shielding. These highly promising materials have traditionally been synthesized by monomer oxidation in the presence of a strong oxidant and, once synthesized, they usually show high insolubility and intractability. The use of enzymes as biocatalysts for the synthesis of conducting polymers has been studied in last years as a ‘‘green synthesis process’’ alternative. Enzymes can offer environmentally benign reaction conditions, a high yield of polymerization, and higher control in regioregularity and stereochemistry, consequently resulting in soluble and processable conducting polymers. In most cases, the research was focused on the synthesis of polyaniline (PANI). According to this biocatalytic approach, the aniline is coupled together by horseradish peroxidase (HRP) or another peroxidase catalyzed oxidation in the presence of an anionic polyelectrolyte or a micellar template leading to a PANI aqueous dispersion. Moreover, in general, the expensive enzymes must be recovered and reused after the reaction for practical applications. This is the main reason behind the well established strategy of immobilization of enzymes into solid supports which was applied to the HRP enzyme. Recently, our group reported the first enzymatic polymerization of 3,4-ethylenedioxythiophene (EDOT), demonstrating that this green synthesis process can be applied to other technologically interesting polymers besides PANI. In this work, a pH of 2 and a Temperature of 4 C were established as optimum conditions for the adequate synthesis of PEDOT. And even if some previous researches reported an abrupt decrease of the enzymatic activity in acidic media (at pH 1⁄4 4, the HRP activity is around 0 after 1 h), in our case, the reaction was observed to proceed uninterruptedly throughout 16 h. Then, we proved that the enhanced enzyme activity was due to the presence of an excess of EDOT in the media (monomer droplets), where the HRP was more preferentially localized. Monomer droplets would act, consequently, as (a) enzyme protectors against deactivation as well as (b) a monomer feed to keep a constant EDOT concentration in the reaction media. In another previous contribution by the authors a biphasic catalytic system was employed as a way to recover and reuse the enzyme several times after aniline polymerization. In this case, the enzyme was encapsulated inside an ionic liquid while the aniline monomer, the H2O2 oxidant, and the template stayed in aqueous Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 306–309 (2009)