Tóm tắt
AbstractSyndiotactic polystyrene (SPS) is a new crystalline engineering thermoplastic. With a melting point of 270 °C and its crystalline nature, SPS has high heat resistance, excellent chemical resistance and water/steam resistance. Since SPS has excellent dielectric properties, it is useful as a capacitor insulation material. The rate of crystallization is very fast in comparison with isotactic polystyrene (IPS), thus, SPS can be used in a number of forming operations, including injection molding, extrusion and thermoforming.A system composed of a homogeneous titanium compound and methylaluminoxane (MAO) is an effective catalyst for syndiospecific polymerization of styrene. On the other hand heterogeneous titanium compounds containing halogen make a mixture of isotactic and syndiotactic components. The amount of syndiotactic polystyrene obtained is dependent on the mole ratio of Al to Ti. The result of ESR measurement suggests the Ti3+ species are important as a highly active site for producing syndiotactic polystyrene.A comparison of the stereoregularities of polypropylene and polystyrene formed by various metallocene catalysts is studied. The (C6H6)2C(η5‐C5H4)(η5‐C9H6)TiCl2/MAO system gives a homogeneous catalyst for the polymerization of propylene giving isotactic rich polypropylene and of styrene to give syndiotactic polystyrene.
