Hyun Joon Kim

The fabrication of syndiotactic polystyrene/organophilic clay nanocomposites and their properties

The fabrication of nanocomposite of syndiotactic polystyrene (sPS)/organophilic clay was conducted by melt intercalation. To avoid the decrease of interlayer spacing due to desorption of organic materials at high temperature, various amorphous styrenic polymers were introduced during the melt mixing process. The nanocomposites were fabricated via two different methods, one is the stepwise mixing method, which is the melt intercalation of amorphous styrenic polymers into organophilic clay followed by blending with sPS, and the other is the simultaneous mixing method, in which all components are melt mixed together. The microstructures of nanocomposites were investigated by X-ray diffraction (XRD) and transmission electron microscopy. The mechanical properties of the nanocomposites such as tensile strength, flexural modulus and izod impact strength were measured and discussed in relation to their microstructures. Both fabrication methods yielded the nanocomposites with different microstructures ranging from intercalated structure to exfoliated structure depending on the kind of amorphous styrenic polymers, which was revealed by the increase in interlayer spacing on X-ray spectrum. Amorphous polymers intercalated into the clay gallery previously is considered to play an important role in maintaining the intercalated or exfoliated structure without any contraction of interlayer spacing even at sPS melting temperature. The fabrication method also influenced the microstructure and mechanical properties, especially tensile strength. In the case of nanocomposites having intercalation structure, the stepwise mixing method yielded more obvious intercalation structure than the simultaneous mixing method so that the former method resulted in higher tensile strength. On the other hand, the nanocomposite having exfoliated structure showed similar mechanical properties between the two fabrication methods.

Copolymerization of ethylene and propylene using catalysts based on titanium compounds modified with trimethylsilanol

Abstract Copolymerization of ethylene and propylene was performed using a catalyst based on TiCl4 modified with trimethylsilanol which is soluble in toluene (diluent used in the polymerization) even after cocatalyst addition. The copolymers were analysed and their structures were found to be very similar to those obtained with vanadium catalysts.

Polymerization of ethylene and propylene with homogeneous titanocene catalysts modified by trimethylsilanol

Abstract Polymerizations of ethylene and propylene were conducted with catalysts based on titanium compounds (TiCl4 or CpTiCl3) modified by trimethylsilanol (TMS). The convenient conditions of catalyst preparation and polymerization were investigated such as ageing time, Si/Ti mole ratio, catalyst concentration, type of alkylaluminum compound used as cocatalyst and Al/Ti mole ratio. The influence of these parameters on the homopolymerization of ethylene and propylene is then described in detail. The polymerization activities were found to be strongly dependent upon catalyst preparation and polymerization conditions. Electron paramagnetic resonance (EPR) analyses were conducted with different Al/Ti mole ratios for elucidating the influence of the Ti oxidation state on the catalyst properties. This work reports a plausible mechanism for the polymerization on the basis of these results.