Preparation of the thermally stable conducting polymer PEDOT - Sulfonated poly(imide)

We describe the template polymerization of EDOT with sulfonated poly(amic acid) (SPAA), resulting in a stable conducting polymer aqueous dispersion, PEDOT-SPAA, with particle size ca. 63 nm. In films of PEDOT-SPAA, the sulfonated poly(amic acid) template undergoes imidization within 10 min at temperatures greater than 150 °C, resulting in PEDOT-sulfonated poly(imide) (PEDOT-SPI) with 10-fold conductivity enhancement. This material is highly thermally stable as compared to PEDOT-PSS. Thermal stability is necessary for many processing applications of conducting polymers, including annealing for OPVs and melt-processing of polycarbonate for device encasement. Isothermal TGA experiments were run at 300 °C for PEDOT-PSS and PEDOT-SPAA and we found that PEDOT-SPAA had a smaller slope for degradation. Annealing of films at 300 °C for 10 min caused the conductivity of PEDOT-PSS films to be unmeasurable (<1 × 10⁻⁵ S/cm), while those of PEDOT-SPAA increased 6-fold. Secondary doping of the PEDOT-SPAA system with additives commonly used for PEDOT-PSS was also investigated.     

Surfactant‐dispersed carbon black in polyimide nanocomposites: Spectroscopic monitoring of the dispersion state in the polymer matrix

The effects of an anionic surfactant on the dispersion of carbon black (CB) for the purpose of forming conducting composite films were examined with ultraviolet–visible (UV–vis) absorption spectroscopy. To obtain a good dispersion and size reduction of aggregated CB in a polymer matrix, sodium dodecyl sulfate (SDS), used as a surfactant, was introduced into a CB suspension. A set of concentrations with various ratios of CB to SDS (ranging from 1 : 0.4 to 1 : 10) was established before mixing with poly(amic acid) (PAA), a precursor of pyromellitic dianhydride and oxydianiline, was performed. The CB/PAA solution mixtures were submerged under an ultrasonic bath for several hours, then cast onto dry plate glasses, and finally subjected to thermal imidization to produce CB/polyimide (PI) nanocomposite films with various CB weight fractions ranging from 0.025 to 0.50 wt %. A method for evaluating the absorbance at 500 nm of the CB/PI nanocomposite films was established. The absorbance of CB/PI nanocomposite samples of various thicknesses was also normalized to get rid of the effects of the different thicknesses. UV–vis spectra showed that the minimum weight ratio of CB to SDS in the nanocomposite films that achieved well‐dispersed CB and still had transparent properties was 1 : 2.0. Transmission electron microscopy demonstrated that CB was dispersed homogeneously in the PI matrix, and the size of the aggregated CB was affected by the amount of the surfactant. The dielectric properties of the nanocomposite films without the surfactant increased by approximately 2 orders of magnitude with an increasing mass weight fraction of CB and decreased when the surfactant was added. The surfactant also reduced the tensile strength of the CB/PI nanocomposites when the CB/SDS ratio was higher than 1 : 2.0. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dielectric properties and solubility of multilayer hyperbranched polyimide/polyhedral oligomeric silsesquioxane nanocomposites

Multilayer hyperbranched polyimide/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized by the reaction of a bromide‐hyperbranched polyether/POSS and a main‐chain polyimide containing hydroxyl‐functional groups. The first layer was formed through the direct reactions of the main‐chain hydroxyl groups with monochloroisobutyl polyhedral oligomeric silsesquioxane (POSS–Cl). The second and third layers were prepared by the repeated reactions of bromine ether branches that incorporated POSS–Cl with 3,5‐dihydroxybenzyl alcohol. Regardless of the fixed amount of POSS, the higher layers yielded lower dielectric constants. Even when the amount of the POSS loading was reduced 4‐fold, the third layer still had the lowest dielectric constants. The lowest dielectric constant of 2.54 was found in the third layer of the hyperbranched polyimide/POSS nanocomposite because of the large free volume and loose polyimide structures. The densities of the hyperbranched polyimide/POSS nanocomposite corresponded to the dielectric constants. The lower the density was, the higher the free volume was and the lower the dielectric constant was. The experimental results indicated that the hyperbranched polyimide/POSS nanocomposite exhibited increased solubility in comparison with pure polyimide. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

New synthesis methods for polypropylene‐co‐ethylene‐propylene rubber

In this research, the reinforcement of polypropylene (PP) was studied using a new method that is more practical for synthesizing polypropylene‐block‐poly(ethylene‐propylene) copolymer (PP‐co‐EP), which can be used as a rubber toughening agent. This copolymer (PP‐co‐EP) could be synthesized by varying the feed condition and changing the feed gas in the batch reactor system using Ziegler–Natta catalysts system at a copolymerization temperature of 10°C. The ¹³C‐NMR tested by a 21.61‐ppm resonance peak indicated the incorporation of ethylene to propylene chains that could build up the microstructure of the block copolymer chain. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA) results also confirmed these conclusions. Under these conditions, the morphology of copolymer trapped in PP matrix could be observed and the copolymer T_g would decrease when the amount of PP‐co‐EP was increased. DMA study also showed that PP‐co‐EP is good for the polypropylene reinforcement at low temperature. Moreover, the PP‐co‐EP content has an effect on the crystallinity and morphology of polymer blend, i.e., the crystallinity of polymer decreased when the PP‐co‐EP content increased, but tougher mechanical properties at low temperature were observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3609–3616, 2007     

Enhancement of poly(3,4-ethylenedioxy thiophene)/poly(styrene sulfonate) properties by poly(vinyl alcohol) and doping agent as conductive nano-thin film for electronic application

In this work, the integration of the useful concepts of polymer blending and doping agent to simultaneously improve various properties of poly(3,4-ethylene dioxy thiophene) poly(styrene sulfonate) (PEDOT:PSS) nano-thin films was shown. According to the polymer-blending concept, insulating poly(vinyl alcohol) (PVA) has a good deal of potential to be utilized as a filler to improve the critical properties of the PEDOT:PSS matrix, especially conductivity, wettability, and thermal and mechanical properties. At the appropriate amount of PVA, 0.08 wt%, it acts as a binder to improve the connection network between PEDOT:PSS chains, leading to a maximum conductivity of 1.18 S/cm, and also providing a good contact angle of 8.8°. The transmission of the films decreased with increasing PVA content; however, all specimens still showed excellent transmittance values of more than 80 %. The thermal stability and the resistance to abrasion of the nano-thin conductive films were improved by strong covalent bonds between PVA and PSS, which were verified by TGA and a scratching test, respectively. In addition, the relationship of PEDOT:PSS properties versus various amounts of insulating PVA for practical usage for specific electronic fields were shown. Use of the doping agent quinoxaline was aimed to particularly enhance the conductivity of PEDOT:PSS. The highest conductivity (2.75 S/cm) was achieved when 0.5 wt% quinoxaline was added into 0.08 wt% PVA/PEDOT:PSS while the other properties were not significantly altered.     

Modification of Novel Conductive PEDOT:Sulfonated Polyimide Nano-Thin Films by Anionic Surfactant and Poly(vinyl alcohol) for Electronic Applications

Conductive poly(3,4-ethylenedioxythiophene):sulfonated polyimide (PEDOT: SPI) nanoscale thin films were successfully developed by addition of anionic surfactant and poly(vinyl alcohol) (PVA) for potential application in electronic devices. In this work, sodium dodecyl sulfate (SDS) surfactant was introduced into PEDOT:SPI aqueous suspensions to improve the dispersion stability of the particles in water, leading to high transparency and low contact angle of PEDOT:SPI thin films. All of the conducting polymer thin films showed high transparency of more than 85% transmission. Conductivity enhancement and good film-formation properties of PEDOT:SPI were achieved by adding various amounts of PVA to each polymer aqueous suspension because of the resulting conformational changes. The highest conductivity of 0.134 S/cm was achieved at 0.08 wt.% PVA in PEDOT:SPI2/SDS/PVA film, increased by a factor of 3.5 compared with the original material. In addition, PVA also improved the thermal stability of the conductive films, as verified by thermogravimetric analysis (TGA). The interactions between conducting polymers, PVA, and SDS surfactant affecting nano-thin film properties were revealed and investigated. Moreover, the interactions between SDS and SPI were proven to be different from those between SDS and poly(styrenesulfonate) (PSS) in conventional PEDOT:PSS solutions.     

Synthesis and characterization of low‐dielectric photosensitive polyimide/silica hybrid materials

Photosensitive polyimide/silica hybrid materials were synthesized by reaction between 4,4′‐hexafluoroisopropylidene diphthalic anhydride (6FDA) and 4,4′‐oxydianiline. The intrachain chemical bonding and the interchain hydrogen bonding between the polyimide and silica moieties were increased by the incorporation of 2‐(dimethylamino) ethyl acrylate and 3‐aminopropyl trimetho xysilane, respectively. The photoinitiator was bis(2,4,6‐trimethyl benzoyl) phenylphosphine oxide (Irgacure‐819). The various coupling agents were utilized included tetrakis (allyloxy) silane (TAL). Most silica hybrid films showed better volume shrinkage and temperature resistance. The cooperation of octavinyl POSS, as the coupling agent, can lower dielectric constant (k) down to 2.48 but with the poorer volume shrinkage and temperature resistance than the other silica hybrid films. The addition of tetramethyl orthosilicate and 3‐methacryloxy propyltrimethoxysilane with silica content of 5.6 wt % can reduce k down to 2.26 but with worse volume shrinkage than the incorporation with TAL. The TAL hybrid film with degree of polymerization of 25 showed the best properties that optimized photolithography, dielectric constant (k = 3.81), volume shrinkage, and temperature resistance (Td5% = 378°C) with only 0.22 wt % silica content. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Alignment of carbon nanotubes in polyimide under electric and magnetic fields

Usually alignment of carbon nanotubes (CNT) in polymer composites can be induced by a single electrical or magnetic field. Here we report a comparison between the results of simultaneous application of both fields to the polyimide composite and a single field. Alignment of CNT in polyimide was performed under a 2 Tesla magnetic field and various electric fields (150, 300, 450, and 600 V/cm). Polarized Raman spectroscopy was used for assessing the degree of alignment of the nanotubes in the composites and many details of the alignment were examined. The results indicated that at the same electric field strength, incorporation of a magnetic field in a given direction will enhance the level of alignment as compared with only using an electric or magnetic field alone. The best alignment condition was for the CNT samples under parallel magnetic and electric fields. Optical microscopy observations also indicated that nanotube alignment appeared at the highest field strength and decreased when the field strength decreased. A possible mechanism for field alignment is presented. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of graft copolymers of syndiotactic polystyrene with polybutadiene and 4‐methylstyrene

The basic method for synthesizing syndiotactic polystyrene‐g‐polybutadiene graft copolymers was investigated. First, the syndiotactic polystyrene copolymer, poly(styrene‐co‐4‐methylstyrene), was prepared by the copolymerization of styrene and 4‐methylstyrene monomer with a trichloro(pentamethyl cyclopentadienyl) titanium(IV)/modified methylaluminoxane system as a metallocene catalyst at 50°C. Then, the polymerization proceeded in an argon atmosphere at the ambient pressure, and after purification by extraction, the copolymer structure was confirmed with ¹H‐NMR. Lastly, the copolymer was grafted with polybutadiene (a ready‐made commercialized unsaturated elastomer) by anionic grafting reactions with a metallation reagent. In this step, poly(styrene‐co‐4‐methylstyrene) was deprotonated at the methyl group of 4‐methylstyrene by butyl lithium and further reacted with polybutadiene to graft polybutadiene onto the deprotonated methyl of the poly(styrene‐co‐4‐methylstyrene) backbone. After purification of the graft copolymer by Soxhlet extraction, the grafting reaction copolymer structure was confirmed with ¹H‐NMR. These graft copolymers showed high melting temperatures (240–250°C) and were different from normal anionic styrene–butadiene copolymers because of the presence of crystalline syndiotactic polystyrene segments. Usually, highly syndiotactic polystyrene has a glass‐transition temperature of 100°C and behaves like a glassy polymer (possessing brittle mechanical properties) at room temperature. Thus, the graft copolymer can be used as a compatibilizer in syndiotactic polystyrene blends to modify the mechanical properties to compensate for the glassy properties of pure syndiotactic polystyrene at room temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009