Novel Chain-End Modification of Polymer Iodides via Reversible Complexation-Mediated Polymerization with Functionalized Radical Generation Agents.

The modification of polymer chain ends is important in order to produce highly functional polymers. A novel chain-end modification of polymer iodides (Polymer-I) via reversible complexation-mediated polymerization (RCMP) with different functionalized radical generation agents, such as azo compounds and organic peroxides, was developed. This reaction was comprehensively studied for three different polymers, i.e., poly (methyl methacrylate), polystyrene and poly (n-butyl acrylate) (PBA), two different functional azo compounds with aliphatic alkyl and carboxy groups, three different functional diacyl peroxides with aliphatic alkyl, aromatic, and carboxy groups, and one peroxydicarbonate with an aliphatic alkyl group. The reaction mechanism was probed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The combination of PBA-I, iodine abstraction catalyst and different functional diacyl peroxides enabled higher chain-end modification to desired moieties from the diacyl peroxide. The dominant key factors for efficiency in this chain-end modification mechanism were the combination rate constant and the amount of radicals generated per unit of time.

Surface Modification of Carbon Fiber for Enhancing the Mechanical Strength of Composites.

The surface of carbon fibers (CFs) is often modified by multi-walled carbon nanotubes (MWCNTs), and the effect of the interface on the mechanical properties has been reported mostly for epoxy matrices. We achieved effective surface modification of CFs by a simple two-step process to graft a large amount of MWCNTs using a highly reactive polymer to enhance the bonding between CFs and MWCNTs. The first step was the reactive mono-molecular coating of a reactive polymer (poly-2-isopropenyl-2-oxazoline; Pipozo) that has high reactivity with COOH from CFs and MWCNTs. The high reactivity between the oxazoline group and COOH or phenol OH was confirmed for low-molecular-weight reactions. The second step was the coating of MWCNTs from a dispersion in a solvent. This simple process resulted in a substantial amount of MWCNTs strongly bonded to CF, even after washing. The MWCNTs grafted onto CFs remained even after melt-mixing. The effect on the interface, i.e., physical anchoring, led to an improvement of the mechanical properties. The novelty of the present study is that Pipozo acted as a molecular bonding layer between CFs and MWCNTs as a physical anchoring structure formed by a simple process, and the interface caused a 20% improvement in the tensile strength and modulus. This concept of a composite having a physical anchoring structure of MWCNTs on CFs has potential applications for lightweight thermoplastics, such as in the automotive industry.

Development of Electrically Conductive Thermosetting Resin Composites through Optimizing the Thermal Doping of Polyaniline and Radical Polymerization Temperature.

This work developed an electrically conductive thermosetting resin composite that transitioned from a liquid to solid without using solvents in response to an increase in temperature. This material has applications as a matrix for carbon fiber reinforced plastics. The composite comprised polyaniline (PANI) together with dodecyl benzene sulfonic acid (DBSA) as a liquid dopant in addition to a radical polymerization system made of triethylene glycol dimethacrylate with a peroxide initiator. In this system, micron-sized non-conductive PANI particles combined with DBSA were dispersed in the form of conductive nano-sized particles or on the molecular level after doping induced by a temperature increase. The thermal doping temperature was successfully lowered by decreasing the PANI particle size via bead milling. Selection of an appropriate peroxide initiator also allowed the radical polymerization temperature to be adjusted such that doping occurred prior to solidification. Optimization of the thermal doping temperature and the increased radical polymerization temperature provided the material with a high electrical conductivity of 1.45 S/cm.

Removal of Trithiocarbonyl End Group of RAFT-Polymerized Poly(stearyl acrylate) and Effect of the End Group on Thermal and Structural Properties.

The effect of a long alkyl end group on the thermal and structural properties of RAFT (reversible addition-fragmentation chain transfer)-polymerized poly(stearyl acrylate) (PSA) was investigated. RAFT-polymerized PSA was prepared using 2-cyano-2-[(dodecylsulfanylthiocarbonyl) sulfanyl] propane (CDTP) with long alkyl group as a chain transfer agent and azobisisobutyronitrile (AIBN) as an initiator. The RAFT polymerization resulted in the polymerized structure having trithiocarbonyl (TTC) at one end and isobutyronitrile at the other end. RAFT-polymerized PSA was prepared with two different molecular weights. The TTC end group was replaced by isobutyronitrile using radical reaction with AIBN through optimization of the conditions, which resulted in isobutyronitrile at both ends. The effect of the end group on the thermal and structural properties was investigated using differential scanning calorimetry and X-ray diffraction, and the results indicated that the long alkyl group from TTC lowers the melting point and semi-crystalline structure in the case of low molecular weight PSA.

Interfacial Engineering in Solution Processing of Silicon-Based Hybrid Multilayer for High Performance Thin Film Encapsulation.

Solution processing of thin film encapsulation (TFE) has been a long anticipated technology to bridge the big idea of flexible organic electronics to become real world values, since only small-sized flexible devices are currently achieved with expensive multilayered TFE by complex vacuum processing. Highly demanding conditions are to carry out the process under inert gas, at a low temperature, and without aggressive chemicals to avoid damages to the organic materials. Here we show for the first time a solution-processed TFE to totally equal the level of conventional glass-cap encapsulation to achieve a "ready-to-be-used" stability of an organic light emitting diode (OLED). A seamless organic/inorganic multilayer in a structure such as polydimethylsiloxane (PDMS)/SiOx/SiNy/SiOxNy with a built-in compositional gradient, as we named "PONT", was achieved by a combination of two Si-based polymer coatings, UV-curable PDMS, perhydropolysilazane (PHPS), and their photochemical conversion under irradiation of vacuum ultraviolet (VUV) light (λ = 172 nm) in an N2-filled glovebox at room temperature. PDMS precursors diluted with decamethylcyclopentasiloxane were directly coated to OLED to form a protective layer. The presence of soft, elastic PDMS and its surface conversion to SiOx to improve wetting resulted in strong adhesion at the interfaces and relaxed strain to avoid cracks in ultrathin and high density SiOxNy to serve as a perfect barrier. A remarkably low water vapor transmission rate <10-4 g/m2/day was confirmed for a single PONT as thin as 280 nm. Standardized OLED devices with PONT TFEs have proven 3,864 and 528 h stability under atmospheric (25 °C, 50% relative humidity (RH)) and accelerated (60 °C, 90%RH) degradation tests, respectively, without formation of nonemissive dark spots in OLEDs. The fast processing of PONT TFE can be applied to roll-to-roll fabrication of various organic devices at low cost and in large areas, since direct solution coating as well as VUV irradiation do not cause any noticeable damages to sensitive organic materials.

Synthesis, characterization, and polarized luminescence properties of platinum(II) complexes having a rod-like ligand.

We have synthesized a series of platinum (Pt) complexes having a rod-like ligand: 'Pt(F(2)PPy)acac', 'Pt(12F(2)PPy)acac', and 'Pt(12F(2)PPyO4)acac'. The crystal form of Pt(12F(2)PPy)acac was successfully determined to be triclinic by single-crystal X-ray structural analysis. The molecules were parallelly aligned in the unit cell. Monomer and excimer emissions of Pt(12F(2)PPy)acac were observed in hexane solution, poly(methyl methacrylate) film, and various nematic LCs. Homogeneous LC cells with the Pt complex/LC mixtures exhibited polarized optical emission resulting from monomer and excimer states. The PL intensity perpendicular to the orientation direction was higher than the parallel one in the whole wavelength region of the Pt complex and the polarization ratio of the excimer was higher than that of the monomer. The polarization ratios of the excimers were estimated to be 1.4-2.5 in nematic LC at room temperature, and decreased gradually with increasing temperature. The polarization ratios of Pt(12F(2)PPyO4)acac were higher than those of Pt(F(2)PPy)acac and Pt(12F(2)PPy)acac in all the LCs.