The Preparation Of POSS Modified Z-N Catalyst And The Synthesis Of Weakly Entangled UHMWPE

Ultra-high molecular weight polyethylene(UHMWPE)is a high molecular polymer with a relative molecular weight exceeding 1×10⁶g/mol.UHMWPE is widely used in plates,pipes,fibers,films,etc.Owing to its excellent impact resistance,wear resistance,and corrosion resistance.At present,commercial UHMWPE contains a large number of chain entanglements because macromolecular chains are entangled with each other.Chain entanglement is a very important physical structure of UHMWPE,which increases the melt viscosity and particle fusion defects,thereby reducing the processing efficiency and mechanical properties of UHMWPE.Therefore,reducing the degree of chain entanglement is vital to expand the UHMWPE application market.Since the 1950s,the three main types of catalytic systems in the olefin polymerization industry are Ziegler-Natta catalysts,metallocene catalysts and late transition metal catalysts.At present,Ziegler-Natta catalyst is still dominant because of its high activity,low cost,and easy control.Polysilsesquioxane(POSS)can be used to modify polyolefin catalysts because of its temperature resistance,spatial cage structure,etc.At present,the catalysts that have been developed for the synthesis of weakly entangled UHMWPE,such as FI catalysts,are only used at low temperatures(?15°C).The activity of FI catalyst is far from the industrial demand,which makes it unable to be applied to existing industrial equipment.Therefore,POSS modified Ziegler-Natta catalyst has become an important direction for industrial production of weakly entangled UHMWPE.Based on the“Separation of catalyst active centers to prepare separated polyethylene segments”,a new Ziegler-Natta catalyst with discrete“polymerization micro-zones”was designed and synthesized by using POSS/MgCl₂nano-aggregates with a particle size of 40-60nm to separate the active centers on SiO₂support.The weakly entangled UHMWPE was successfully synthesized by the catalyst at 80°C.The properties and polymerization process of weakly entangled UHMWPE were studied.And the polymerization reaction is amplified in industrial equipment.The specific work includes three aspects:(1)Preparation of SiO₂/MgCl₂/POSS/TiCl₄catalyst and research on ethylene polymerization;(2)Optimizing components of catalyst and the polymerization process of weakly entangled UHMWPE;(3)Research amplification polymerization on industrial equipment.1.POSS/MgCl₂nanoaggregates with steric barrier are synthesized by POSS coordinated MgCl₂molecules.POSS/MgCl₂builds"polymerization micro-zones"by isolating active centers on the SiO₂ framework.The structure of the catalyst shows that POSS/Mg Cl₂ forms nano-aggregates with a particle size of 40-60 nm on the surface of SiO₂.Combined with the research results of rheology,POSS/MgCl₂nano-aggregates successfully separated the polyethylene chain.Combined with the research results of mechanical properties,weakly entangled polyethylene molecular chains are easier to diffuse during processing,which can effectively reduce the defects of the fusion interface of UHMWPE particles and improve the impact strength.2.We made a research about the properties and polymerization process of weakly entangled UHMWPE.The effects of catalyst components and polymerization conditions on polymerization activity,molecular weight,chain entanglement,mechanical properties,etc.were investigated by controlling TiCl₄,MgCl₂,SiO₂,time,temperature and co-catalyst.According to the requirements of industrial production,we selected the best polymerization conditions of weakly entangled UHMWPE.3.Based on the polymerization conditions selected in the previous chapter,we conducted polymerization reactions in 1 L,10 L and 300 L reactors to investigate the industrial application potential of the catalyst.The activity of ethylene polymerization is 20 kg PE/(g Cat·h)in a 300L reactor.A series of UHMWPE with a viscosity average molecular weight of2.1-7.6×10⁶g/mol has been synthesized.They not only have weaker chain entanglements but also stronger mechanical properties.Compared with industrial UHMWPE,it's tensile strength,impact strength and elongation at break are increased by 23.9%,22.1%and 15.4%.