Sung Woo Nam

Preparation and properties of conducting arachidic acid/polypyrrole composite Langmuir-Blodgett films

Electrically conducting arachidic acid/polypyrrole (PPy) composite films were prepared by exposing the arachidic acid LB films containing ferric chloride to pyrrole vapor. The optimum conditions to deposit matrix LB film were the subphase temperature of 23-25°C, pH of 6.0 and ferric chloride concentration of 5.0 X 10 -5 M. The formation of PPy in the arachidic acid matrix LB films was confirmed by UV-visible spectra, FTIR spectra, and scanning electron micrographs. The average thickness of the composite LB films prepared at 0°C was 1525 A. The composite films prepared at lower temperatures have more uniform surface and exhibit higher electrical conductivity than the films prepared at higher temperatures do. The in-plain conductivity and the transverse conductivity of the composite film were 10 -3 -10 -2 S/cm and 10 -6 S/cm, respectively, and, thus, the conductivity anisotropy was about 10 3 .

Preparation, chemical, and thermal characterization of nylon 4/6 copolymers by anionic ring opening polymerization of 2-Pyrrolidone and ε -Caprolactam

Nylon 4/6 copolymers based on 2-pyrrolidone (C4) and ε-caprolactam (C6) were synthesized and characterized as part of ongoing efforts to develop thermally stable, melt-processable 2-pyrrolidone (C4) based Nylons. Copolymers of various compositions were synthesized at between 50 and 100 °C via the anionic ring opening polymerization of C4 and C6 using a potassium tert-butoxide catalyst and a benzoyl chloride initiator. The polymers were characterized by NMR spectroscopy, DSC, TGA, GPC, intrinsic viscosity measurements, and X-ray scattering (SAXS and WAXS). Their chemical compositions and sequence distributions were obtained by 1H- and 13C-NMR spectroscopies, respectively. X-ray scattering was used to investigate the lamellar morphologies and the crystal structures of solvent cast films of the copolymers. WAXS revealed the presence of α-phase crystals in the copolymers. TGA data coupled with molecular weight and sequence distribution information indicated that the polymers’ thermal stability depended on both their chemical composition and their sequence distribution.

Synthesis of poly(2,6-dimethyl-1,4-phenylene ether) with controlled molecular weight via suspension polymerization catalyzed by amine–copper (I) complexes under various reaction conditions

The oxidative suspension polymerization of 2,6-dimethyl phenol (DMP) to poly(2,6-dimethyl-1,4-phenylene ether) (PPE) was performed with the use of emulsifier in water–chloroform biphasic medium. The effects of DMP/catalyst mole ratio, ligands, emulsifiers, and 2,4,6-trimethyl phenol on polymerization were investigated in terms of molecular weight and yield. Various ligands were employed in the polymerization to investigate ligand efficiency. Intrinsic viscosity measurement data showed that the most efficient ligand was 1-methyl imidazole (Meim) in terms of molecular weight. By incorporating different amount of DMP in the monomer feed, it was possible to control the molecular weight of PPE in the oxidative suspension polymerization.

Synthesis of poly(glycolic acids) via solution polycondensation and investigation of their thermal degradation behaviors

Polyglycolic acid (PGA) was successfully synthesized via solution and melt/solid polycondensations. PGA was synthesized by solution polymerization under vacuum by using diphenylsulfone as solvent and methanesulfonic acid as catalyst and the inherent viscosity of resultant PGA was 0.2 dl/g. The intrinsic viscosity was obtained up to 0.35 dl/g of the PGA synthesized by melt/solid polycondensation. Whereas, PGA synthesized by longer hours of SSP was insoluble in most of the known solvents, which might have higher molecular weight as well as crystallinity. Crystallographic structure of PGA was confirmed by XRD and the resulting PGA polymer was similar in thermal degradation to that of commercially available polyglycolide (Kuredux), synthesized by ring opening polymerization. Both PGAs were characterized for thermal decomposition kinetic studies using thermaogravimetric analysis (TGA), to investigate the effect of end-group and molecular weight on thermal degradation behavior. TGA was performed at 6 different heating rates from 5 to 50 °C/min and data was analyzed by three different approaches to obtain activation energy. Activation energy from Kissinger’s approach was 112 kJ/mol for lab synthesized PGA and 119 kJ/mol for Kuredux, whereas from Flynn and Wall’s method, it was observed as 115 kJ/mol and 121 kJ/mol for solution-polymerized PGA and Kuredux respectively and activation energies calculated from dynamic experiment method was also comparable of both PGAs. From dynamic experiment method linearity curve starts as low as 1 % decomposition and continues as high as 97 % with decomposition temperature ranges 219 to 380 °C for PGA and 230 to 406 °C for Kuredux. Consequently, Kissinger’s method, Flynn and Walls method and the dynamic experiment method reveal that the thermal decomposition behavior of polyglycolic acids and polyglycolide is similar, regardless of end groups and synthetic routes which is supposed to be random chain cession.

Synthesis of poly(norbornene ester)s by using (η 3-substituted allyl) palladium (NHC) complex as catalyst and investigation of their chemical structure - Glass transition temperature - Refractive index relationships

The synthesis of poly(norbornene ester)s by using a (η3-substituted allyl) palladium (N-heterocyclic carbene (NHC)) complex as catalyst was performed and the relationship between chemical structure and glass transition temperature or refractive index of poly(norbornene ester)s was investigated. Norbornene ester monomers were synthesized via esterification of 5-norbornene-2-methyl alcohol and aromatic carboxylic acids. The polymerization catalyst, (η3-substituted allyl) palladium (NHC) complex, was synthesized according to a published procedure. 1H-NMR spectroscopy was performed to determine chemical structure of monomers and polymers. The molecular weight of the polymers was measured via gel permeation chromatography and the thermal properties were analyzed via thermogravimetric analysis and dynamic mechanical analysis. Refractive indices of polymer films were measured using a prism coupler. Polymers with the highest Mn (between 100 kg/mol and 300 kg/mol) were synthesized when the ratio of monomer to catalyst was 2000:1. The glass transition temperature of synthesized polymers was about 100 °C lower than that of conventional norbornene polymers. Among the six polymers of different chemical structures, four polymers exhibited a refractive index of 1.6 or more at a wavelength in the visible light region.