Yeong Soon Gal

Synthesis and properties of conjugated cyclopolymers bearing fluorene derivatives

Fluorene-containing, spiro-type, conjugated polymers were synthesized via the cyclopolymerization of dipropargylfluorenes (2-substituted, X=H, Br, Ac, NO2) with various transition metal catalysts. The polymerization of dipropargylfluorenes proceeded well using Mo-based catalysts to give a high polymer yield. The catalytic activities of the Mo-based catalysts were found to be more effective than those of W-based catalysts. The palladium (II) chloride also increased the polymer yield of the polymerization. The polymer structure of poly(dipropargylfluorene) s was characterized by such instrumental methods as NMR (1H-,13C-), IR, UV-visible spectroscopies, and elemental analysis as having the conjugated polymer backbone bearing fluorene moieties. The13C-NMR spectral data on the quaternary carbon atoms in polymers indicated that the conjugated cyclopolymers have the six-membered rings majorly. The poly(dipropargylfluorene) derivatives were completely soluble in halogenated and aromatic hydrocarbons such as methylene chloride, chloroform, benzene, toluene, and chlorobenzene. The poly(dipropargylfluorene) derivatives were thermally more stable than poly(dipropargylfluorene) itself, and X-ray diffraction analyses revealed that the polymers are mostly amorphous. The photoluminescence peaks of the polymers were observed at about 457–491 nm, depending on the substituents of fluorene moieties.

Cyclopolymerization of α-methylbenzyl dipropargylamine by transition metal catalysts

π-Conjugated oligomers and polymers are intensively studied mainly because of their interesting electrical and optical properties and, more importantly, their potential utility in electronics and photonic applications. Among the π-conjugated polymers, the polyacetylene (PA) is structurally the simplest one, and it can be made freestanding thin film by using Shirakawa catalysts [Ti(OC4H9)4Al(C2H5)3]. 6 However, the drawbacks are that PA is insoluble, infusible, and unstable to air oxidation. Thus it was difficult for practrical applications to opto-electronic devices as an active material. To overcome these problems of PA itself, more stable heterocycle-based polymers such as polypyrrole and polythiophene were prepared, and these materials can be easily obtained in their oxidized conducting form by means of one-step electrochemical synthesis. And also, a number of substituted PAs has been prepared by the simple linear polymerization of the corresponding acetylene monomers by various catalyst systems. The polymers having a conjugated backbone are expected to show unique properties such as electrical conductivity, paramagnetism, migration and transfer of energy, color, and chemical reactivity and complex formation ability. Because of these properties, polyacetylene and its homologues have been promising as organic semiconductors, as membranes for gas separation and for liquid-mixture separation, as chiro-optical materials, as side-chain liquid crystals, and as materials for nonlinear optical property and for photoluminescence and electroluminescence properties. Cyclopolymerization of nonconjugated diynes is very interesting method for the synthesis of conjugated polymer system via an alternating intramolecular-intermolecular chain propagation. 1,6-Heptadiyne itself has been polymerized by various transition metal catalysts into a polyene of cyclic structure. The resulting poly(1,6-heptadiyne)s obtained were dark red or black, which indicates a high order of conjugation in the polymer. However, the poly(1,6-heptadiyne)s were also insoluble in any organic solvent and unstable to air oxidation as like with that of PA. Introduction of substituents at 4-position of 1,6-heptadiyne can help enhance the processibility and stability of the polyene systems, thus a variety of substituted poly(1,6-heptadiyne)s were designed and synthesized. In recent years, nitrogen-containing polymers have received unabated attention in the design and synthesis of multifunctional polymers. Unlike other π-conjugated polymers, they contain nitrogen heteroatom either in the main chains or in the side chains that provide facile quaternarization reaction and protonation of the nitrogen sites. Now, we report the synthesis of new conjugated cyclopolymer by the cyclopolymerization of a dipropargylamine derivative and the characterization of the resulting conjugated polymer.

Synthesis and Properties of Poly[2-ethynyl-N-(p-hydroxyphenylethyl) pyridinium bromide] and Poly[2-ethynyl-N-(p-hydroxyphenylethyl) pyridinium tetraphenylborate]

A new hydroxyl group-containing conjugated ionic polymer, poly[2-ethynyl-N-(p-hydroxyphenylethyl)pyridinium bromide], was synthesized by the activated polymerization of 2-ethynylpyridine withp-(2-bromoethyl) phenol without any additional initiator or catalyst. The polymerization proceeded well to give a moderate yield (65%) of polymer at a reaction temparature of 90°C. Another polymer, poly[2-ethynyl-N-(p-hydroxyphenylethyl)pyridinium tetraphenylborate], was readily prepared by the ion-exchange reaction of poly[2-ethynyl-N-(p-hydroxyphenylethyl)pyridinium bromide] with sodium tetraphenylborate. These polymers were completely soluble in organic solvents such as DMF, DMSO, and acetone, but insoluble in water and ether. Instrumental analyses, such as NMR, IR, and UV-Vis spectroscopies, indicated that the new materials have conjugated polymer backbone systems with the designed substituents and counter anions. X-Ray diffraction analyses of the polymers indicated that they were mostly amorphous.

Polymerization of bis(3-trimethylsilyl-2-propynyl)ether and its copolymerization with diethyl dipropargylmalonate

The polymerization of a cyclopolymerizable disubstituted dipropargyl ether, bis(3-trimethylsilyl-2-propynyl)ether (BTPE), was attempted by various transition metal catalysts. The yield for the polymerization of BTPE was generally low, which is possibly due to the steric hindrance of bulky substituents. In general, the catalytic activities of Mo-based catalysts were found to be greater than those of W-based catalysts. The highest yield was obtained when the MoCl5-EtAlCl2 (1:2) catalyst system was used. The copolymerization of BTPE and diethyl dipropargylmalonate yielded a random copolymer with conjugated polymer backbone. However the polymers were partially desilylated, depending on the reaction conditions. The thermal and morphological properties of the resulting polymers were also discussed.

Synthesis of Poly(ϵ-caprolactone) Grafted Poly(2-hydroxyethyl methacrylate) Functionalized Hydroxyapatite by RAFT and ROP

Poly(ϵ-caprolactone) grafted poly(2-hydroxyethyl methacrylate) functionalized hydroxyapatite (HAP@PHEMA-g-PCL) nanocomposites were synthesized by the combination of reversible addition fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). The RAFT agent was anchored on the surface of hydroxyapatite nanocrystals (HAPs) through the silane condensation process of 3-chloropropyltrimethoxysilane followed by reaction with potassium xanthogenate. Poly(2-hydroxyethyl methacrylate) (PHEMA) was covalently functionalized on the surface of HAPs by RAFT polymerization. Then, poly(ϵ-caprolactone) (PCL) was grafted on HAPs by ROP based on the hydroxyl groups of PHEMA to afford HAP@PHEMA-g-PCL. The structure and composition of HAP@PHEMA-g-PCL nanocomposites were characterized by FT-IR, XRD, and TGA analyses. The morphology and formation of the polymer encapsulating HAPs were demonstrated from SEM and TEM images, while the 1H MNR analysis of the cleaved PHEMA-g-PCL confirmed the grafting.

Preparation of Silica/Poly(divinylbenzene) Composite Particles by Dispersion Polymerization in Supercritical Carbon Dioxide

Silica/poly(divinylbenzene) (PDVB) composite particles were synthesized by the dispersion polymerization of divinylbenzene (DVB) with ultrafine silica particles in supercritical carbon dioxide (scCO2). Silica particles of average diameter 130 nm were pretreated with 3-(trimethoxysilyl) propyl methacrylate in order to be well dispersed in CO2 and participated in the polymerization. Random copolymeric dispersant, poly(diisopropylaminoethyl methacrylate-co-heptafluorobutyl methacrylate) was used as a stabilizer to provide sufficient stabilization to latexes in scCO2 and the silica/PDVB composite powder was obtained in high yield from the polymerization. SEM analysis revealed that the composite particles prepared at 5% silica loading ratio and 6% stabilizer concentration with respect to monomer have the average diameter of 1.60 μm with uniform and spherical morphology. The composites were also characterized by FTIR spectroscopy and TGA.

Multiple Morphologies of Self-Assembled Amphiphilic Poly(FOMA-b-EO) Diblock Copolymers

A series of well defined semifluorinated diblock copolymers of poly(1H,1H-dihydroperfluorooctyl methacrylate)-block-polyethylene oxide (poly(FOMA-b-EO)) were used for the preparation of self-assembled structures. The morphologies of the poly(FOMA-b-EO) aggregates formed from solvent casting were investigated in terms of the copolymer composition, the concentrations of copolymer solutions, and the solvent type. From CHCl3, the micellar film morphologies of poly(FOMA-b-EO20k) were found to be well-ordered spherical and interconnected rods aggregates when PFOMA block sizes were 10 k (or 20 k) and 80 k. The aggregates were also found to depend strongly on the copolymer concentration. On the other hand, the morphological phase of block copolymeric micelles was inverted in trichlorofluoromethane (CFC-11) solution which is a good solvent for PFOMA, and aggregates were formed with PFOMA as a corona and PEO as a core. Morphological variations were also achieved by using different solvents such as N,N-dimethylformamide (DMF) and methanol, where the aggregates formed were vesicles and lamella with rods.

Aggregates Formed by Poly(Ethylene Oxide)-b-Poly(1H, 1H-Perfluorooctyl Methacrylate) Diblock Copolymers in Solutions

Well-defined block copolymers consisting of a hydrophilic poly (ethylene oxide) (PEO) and lipophobic poly (1H,1H-perfluorooctyl methacrylate) (PFOMA) were synthesized with controlled molecular weight via atom transfer radical polymerization (ATRP). The block copolymers formed stable micelles where PEO is the shell and PFOMA is the core in chloroform. The micellar morphology of PEO5K-b-PFOMA5K was found to be spherical with average diameter of ca. 12 nm, while meandering cylindrical with average diameter of ca. 13 nm was observed for PEO5K-b-PFOMA13K by TEM analysis. The self-assembled structures were reorganized to thermodynamically stable morphologies upon annealing above glass transition temperature (Tg). For example, spherical shape of PEO5K-b-PFOMA5K and cylindrical domain of PFOMA block in PEO5K-b-PFOMA5K became ordered cylindrical and continuous phase, respectively.

Preparation of Highly Dispersed Gold Nanoparticles on Organosilane Modified Graphene Nanosheets

In this study, we present a novel strategy for the immobilization of gold nanoparticles (AuNPs) on the surfaces of modified graphene oxide (MGO/Au) using (3-mercaptopropyl) trimethoxysilane as a bridging agent. In the fabrication process, the hydroxyl functionalized GO was covalently functionalized with (3-mercaptopropyl) trimethoxysilane through C‒O‒Si linkage and the terminal thiol groups were further used to fabricate MGO/Au hybrids via the specific interaction between ‒SH and Au. The degree of covalent functionalization and fabrication of MGO/Au hybrid materials were confirmed with Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermal gravimetric analysis and high resolution transmission electron microscopy (HRTEM) analyses. HRTEM images demonstrated that the AuNPs were homogeneously distributed on the surfaces of GO. The MGO/Au hybrid showed enhanced thermal stability due to the intrinsic properties of graphene and gold nanoparticles.

Preparation of High Molecular Weight Poly(vinyl carbazole)/Polystyrene Blend Web by Electrospinning

To prepare fine and even poly(N-vinyl carbazole) (PVCz)/polystyrene (PS) blend webs, we performed a series of experiments varying processing parameters, including the type of solvent, PVCz/PS blend ratio, applied voltage, and tip to the collector distance (TCD). It was found that the morphology and the average diameter of PVCz/PS blend web were strongly correlated with electrospinning conditions. The morphologies of PVCz/PS blend webs were beaded or fine fibre structures, depending on the blend ratio of PVCz and PS. Increasing content of PS in the spinning solution tended to produce higher spinnability and the average diameter of electrospun web became smaller. The average diameter of the PVCz/PS blend web was slightly decreased with increasing applied voltage. In the case of TCDs, there was no significant effect on the PVCz/PS blend web morphologies but on increasing the TCD, the average diameter of the PVCz/PS blend webs slightly decreased.