Study On The Syndiotactic Polymerization Process Of Styrene By Metallocene Catalysts

Syndiotactic polystyrene (sPS) is a new type of thermoplastics. Recently it becomes focus of research for its excellent properties.In the thesis, a homogenous metallocene catalyst system, Cp*TiX3/MAO/TIBA was used to prepare the syndiotactic polymer. The kinetics of the solution polymerization process, the particle morphology of the produced sPS, and the rheology of the sPS suspension were studied. A seeded semi-continuous polymerization process was investigated also.The styrene syndiotactic solution polymerization were carried out respective in the presence of chlorobenzene, tolune, heptane, isooctane, naphthane and mixed solvent. The results demonstrate that elevating the polymerization temperature and agitation speed, reducing polarity of solvent or using non-solvent for amorphous polystyrene are beneficial to polymerization and raise monomer conversion. And the molecular weight of produced polymer is increased with decrease in temperature and solvent polarity, and with an increase in agitation rate.The investigation on crystallization kinetics of nascent sPS shows that the crystal of nascent sPS from solution polymerization is in 6 type and does not change with variety of solvent. The data of particle size and particle size distributions of the produced polymer during the polymerization indicates that elevating polymerization temperature and agitation speed, and using isooctane or naphthane to be solvent will improve the morphology of nascent particles.By investigating the rheology of sPS suspension, we found that the sPS-chlorobenzene suspension has Newtonian fluid properties when the polymer content is lower than -10%. But suspension will be shear-thinned and turn into the Non-Newtonian fluid with an increase in the sPS content. When the solid content is relative high, temperature rising will decrease shear stress and apparent viscosity. However, when the suspension is prepared by a non-solvent for amorphous polystyrene, such as heptane and isooctane, and the sPS content is lower than 15%,the fluid is Newtonian.The seeded semi-continuous bulk syndiotactic polymerization of styrene is achieved in a 500mL reactor. During the polymerization process, the complicated phase change, the gelation and the reactor fouling can be avoided efficiently.