(226ad) Preparation of in Situ Anti-Sticking Supported Catalysts and Its Applications in Gas-Phase Polymerization
Gas-phase polymerization becomes dominant because of its economical and environmental benefits. However, the sticking characterization of the resulting polymers is a fatal problem that hinders the industrialization of gas-phase polymerization process for rubbers, such as polyisoprene and ethylene-propylene rubber.
An exploratory research was carried out on in-situ preparation of polyisoprene and ethylene-propylene rubber particles by gas-phase polymerization. A new method of preventing agglomeration of rubber particles was proposed. The selected catalyst system and nano-SiO2 were both supported on micron-size silica to prepare the anti-sticking supported catalysts. During polymerization, nano-SiO2stayed on the surface of the particles and formed a barrier layer, which should be effective for preventing agglomeration of the polymeric particles.
For the in-situ preparation of polyisoprene rubber particles, Nd(OiPr)3/MAO/tBuCl was selected as the catalyst system. Morphology of products’ particles, polyisoprene microstructure, molecular weight(MW) and molecular weight distribution(MWD), and polymerization activity were measured. It was found that with the increase of nano-SiO2, the particle agglomeration is suppressed while polymerization activity decreases, and MW and MWD increase; the content of cis-1,4-unit tends to decrease. The microstructure of polyisoprene does not change significantly.
For the in-situ preparation of ethylene-propylene rubber particles by gas-phase polymerization, rac-[Et(Ind)2]ZrCl2/MAO was selected as the catalyst system. Morphology of ethylene-propylene rubber particles, microstructure, MW and MWD, and polymerization activity were characterized. Similarly, using nano-SiO2 could effectively prevent the agglomeration of ethylene-propylene rubber particles. Polymerization activity decreased, while microstructure slightly changed when nano-SiO2was introduced.
In summary, non-sticky polyisoprene rubber particles and ethylene-propylene rubber particles were in-situ prepared successfully in gas-phase polymerization by this novel method. A path to solve the common key problem of rubber particles’ agglomeration was proposed.