Synthesis of monomers and polymeric precursors to impart processability and patternability to conducting polymers

Date of Completion

January 2006


Chemistry, Polymer




Low band gap conducting polymers (CPs) have relatively low absorption in the visible region, in their conducting states, making them promising candidates for optically transparent electrode and hole-injection layer for light-emitting diodes. The monomer, thieno[3,4-b]furan, was electrochemically and chemically polymerized to produce a new conducting polymer, poly(thieno[3,4- b]furan) (PT34bF), having a low band gap of 1.03 eV. The polymer shows good stability and optically properties for its application as an optically transparent conductor. Theoretical data in correlation with the experimental results indicate that connectivity of poly(thieno[3,4-b]furan) is through C4-C6, resulting in predominantly linear PT34bF. ^ CPs are generally insoluble and infusible owing to their rigid backbone, which makes them difficult to process. Sotzing et al. reported a new technique termed as solid-state oxidative conversion (SCC) to enhance the processability of CPs, where precursor homopolymer was converted in the processed form into conducting polymer. Here, thermal and physical properties of precursor polymers were controlled by synthesizing various compositions of random precursor copolymers having pendant electroactive, and non-electroactive units. Two different electroactive groups, dioxythiophene)-N-alkyl-carbazole, were used in this study. Precursor copolymers were processed into thin film via spin, spray, and drop casting and into nanofibers via electrostatic spinning. The optical and electrical properties of CPs obtained from precursor copolymers were tuned by varying the copolymer compositions or using different electroactive groups. The precursor copolymer approach was further extended to introduce additional functionality such as photocrosslinkable groups, methacrylate or cinnamate. The precursor terpolymers having pendant photocrosslinkable units were micro-patterned via photolithography, and then converted into conducting polymer pattern via SOC. Photocrosslinking at the precursor stage can be used to perform SOC in other solvents which may change the polymerization or redox behavior of CPs by having different degree of swelling during SOC. ^ In a different approach, alternate poly(arylsilane) copolymer precursor was prepared via condensation polymerization. The advantage of this method over the previous one is the easy, inexpensive, and single-step synthesis of precursors from monomers. The precursor was converted into conjugated polymer in solid-state via electrochemical and chemical desilylation followed by coupling. The resulting CPs showed electrochemical and optical properties similar to that obtained from monomer solution using conventional electropolymerization. Both SOC processes mentioned above were performed with conducting or insulating, and rigid or flexible substrates. ^