Hohyoun Jang

Synthesis and characterization of polycarbonates containing terminal and chain interior siloxane

Silicone polycarbonates having polydimethyl siloxane (PDMS) and heptamethyl trisiloxane (HMTS) were synthesized by the interfacial polymerization. Instead of common chain terminator p-tert-butyl phenol (PTBP), eugenol capped HMTS, and PDMS were used. PDMS was also attached into the chain interior of the polymer in different molar ratios. PDMS and HMTS were capped with eugenol through the hydrosilylation reaction using Karstedt’s catalyst. Both monohydroxy and dihydroxy terminated eugenosiloxanes were synthesized in order to use as chain terminator and interior subunit of polymer, respectively. Structural characterization and the study of the properties, such as thermal behavior, thermooxidative stability, surface morphology, wettability of the synthesized polymers were investigated. Flexibility and wettability of the synthesized polymers increases with increasing of silicone content. Polymers showed satisfactory thermo oxidative stability and transparency as good as bisphenol-A-polycarbonate.

Anion conductive aromatic ionomers containing a 1,2-dibenzoylbenzene moiety for alkaline fuel cell applications

Novel anion-exchange membranes with high conductivities have been prepared for application to alkaline fuel cells. A quaternary ammonium poly(dibenzoylbenzene ether sulfone) membrane was synthesized by chloromethylation, followed by substitution with trimethylamine with an ion-exchange reaction. The quaternary ammonium groups were selectively substituted in the para-position of the pendant phenyl groups of the dibenzoylbenzene unit. The di-quaternary ammonium hydroxide polymers showed an elevated molecular weight and exhibited excellent solubility in polar aprotic solvents. Quaternization and the subsequent ion-exchange reactions were quantitative such that the obtained ionomer membranes had a high ion-exchange capacity (IEC) of up to 1.69 mmolg−1. The resultant polymer membranes were studied by 1H NMR, FT-IR, thermogravimetric analysis (TGA), IEC, water uptake analysis, and ion conductivity analysis.

Synthesis and Characterization of Polycarbonate Copolymers Containing Benzoyl Groups on the Side Chain for Scratch Resistance

The purpose of this study was to enhance the scratch resistance of polycarbonate copolymer by using 3,3′-dibenzoyl-4,4′-dihydroxybiphenyl (DBHP) monomer, containing benzoyl moieties on the ortho positions. DBHP monomer was synthesized from 4,4′-dihydroxybiphenyl and benzoyl chloride, followed by the Friedel-Craft rearrangement reaction with AlCl3. The polymerizations were conducted following the low-temperature procedure, which is carried out in methylene chloride by using triphosgene, triethylamine, bisphenol-A, and DBHP. The chemical structures of the polycarbonate copolymers were confirmed by 1H-NMR. The thermal properties of copolymers were investigated by thermogravimetric analysis and differential scanning calorimetry, and also surface morphologies were assessed by atomic force microscopy. The scratch resistance of homopolymer film (100 μm) changed from 6B to 1B, and the contact angle of a sessile water drop onto the homopolymer film also increased.

Studies of Grafted and Sulfonated Spiro Poly(isatin-ethersulfone) Membranes by Super Acid-Catalyzed Reaction

Spiro poly(isatin-ethersulfone) polymers were prepared from isatin and bis-2,6-dimethylphenoxyphenylsulfone by super acid catalyzed polyhydroxyalkylation reactions. We designed and synthesized bis-2,6-dimethylphenoxyphenylsulfone, which is structured at the meta position steric hindrance by two methyl groups, because this structure minimized crosslinking reaction during super acid catalyzed polymerization. In addition, sulfonic acid groups were structured in both side chains and main chains to form better polymer chain morphology and improve proton conductivity. The sulfonation reactions were performed in two steps which are: in 3-bromo-1-propanesulfonic acid potassium salt and in con. sulfuric acid. The membrane morphology was studied by tapping mode atomic force microscope (AFM). The phase difference between the hydrophobic polymer main chain and hydrophilic sulfonated units of the polymer was shown to be the reasonable result of the well phase separated structure. The correlations of proton conductivity, ion exchange capacity (IEC) and single cell performance were clearly described with the membrane morphology.

Preparation and characterization of sulfonated poly (ether sulfone)s containing hexabenzocoronene graphene moiety for PEMF

The novel sulfonated poly(ether sulfone)s containing hexabenzocoronene moiety that is partial graphene structure (SPGHPs) for polymer electrolyte membrane were synthesized and characterized their properties. Graphene is an allotrope of carbon and one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Poly(ether sulfone)s containing hexaphenylbenzenes on polymer backbone were synthesized by poly condensation and followed intra-cyclization by friedel-craft reaction with lewis acid (FeCl3) to form partial graphene structure. The sulfonation was taken selectively on hexabenzocoronen units with concentrated sulfuric acid. The structure properties of the sulfonated polymers were investigated by 1H-NMR spectroscopy. The resulted ion exchange capacities (IEC) were 1.09~1.61 meq./g. The water uptakes were 8.84~15.27% at 30 °C and 18.27%~42.38% at 80 °C with changing the ion exchange capacities. The SPGHP membranes exhibit proton conductivities (80 °C, RH 90) of 78.3~105.7 mS/cm compared with 106.2 mS/cm of Nafion 211®.

Anion conductive imidazolium-based Parmax alkaline membrane for fuel cell applications

The anion exchange polyphenylene membrane containing imidazolium hydroxide ionic functional group was synthesized by sequential chloromethylation, substitution with 1-methylimidazole and ion exchange. The imidazolium hydroxide Parmax 1200 membrane has all carbon-carbon bonds without ether linkages, which would be chemically strong. The polyphenylene structure of Parmax provides a stiff and resistant backbone, whereas the pendant benzoyl group provides sites for chemical modifications. The resulting ionomer membrane showed ion exchange capacity (IEC) of 2.14 mmol g-1 with maximum chloromethylation yield. The imidazolium-functionalized copolymer membrane showed lower water affinity and high durability in alkaline condition. It exhibited hydroxide ion conductivity above 10-2 S cm-1 at room temperature and good chemical stability for up to seven days without significant losses of ion conductivity. The structural properties of the synthesized polymer membrane were investigated by 1H NMR spectroscopy and FT-IR. The membranes were studied by IEC, water uptake, and conductivity assessment.

Synthesis and properties of sulfonated poly(N-methylisatin-biphenylene) proton exchange membrane by superacid-catalyzed polymerization

A series of poly(phenylene)-based polyelectrolytes were synthesized from trifluoroacetophenone and N-methylisatin by superacid catalyzed polyhydroxyalkylation reaction. Postsulfonation of this high molecular weight and thermochemically stable poly(phenylene) with concentrated sulfuric acid resulted in homogeneous polyelectrolytes with controllable ion content (IEC: 1.40–2.39 meq./g). All these membranes were casted from dimethylsulfoxide (DMSO). The structural properties of the synthesized polymers were investigated by 1H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability and proton conductivity assessment by comparing with Nation. The polymers containing fluoro group without ether linkage on polymer backbone were chemically stable towards nucleophiles (H 2 O, hydrogen peroxide, hydroxide anion and radical).

Characteristics of Fe powders prepared by spray pyrolysis from a spray solution with ethylene glycol as the source material of heat pellet

Fe powders as the heat pellet material for thermal batteries are prepared from iron oxide powders obtained by spray pyrolysis from a spray solution of iron nitrate with ethylene glycol. The iron oxide powders with hollow and thin wall structure produce Fe powders with elongated structure and fine primary particle size at a low reducing temperature of 615 °C. The mean size of the primary Fe powders with elongated structure decreases with increasing concentration of ethylene glycol dissolved into the spray solution. The heat pellets prepared from the fine-size Fe powders with elongated structure have good ignition sensitivities below 1 watt. The heat pellets formed from the Fe powders obtained from the spray solution with 0.5 M EG have an extremely high burn rate of 26 cms−1.