Preparation Of Polyethylene/Polypropylene-Polyethylene Block Copolymer Alloy Based On Hydrozirconation And Coordination Polymerization

Over 80 million tons of polyolefins are produced currently in the world,and they comprise a large fraction of the plastics in use.Their widespread use has been made possible by important advances in production and processing technology.Among them,polypropylene(PP)as one of the most important class of high polymer materials is applied in electronic appliances?industrial?agricultural and daily life in various fields due to its various excellent performance.Nonetheless,the high crystallinity of PP results in the poor compatibility with most materials,which limits its use in industrial production.At present,the physical blending method is widely used in the modification of polymer materials.For example,the mechanical properties and performance of PP can be improved by physically blending of PP and PE.But how to improve its interface compatibility and then ameliorate performance is the key scientific problem need to be solved.This paper based on the blending modification of PP and PE,the compatibility of PP and PE was improved by the introduction of PP/PE block copolymer,which synthesized by the hydrozirconation and coordination polymerization.The results were characterized by high temperature NMR?high temperature GPC?DSC?stress-strain tests?linear melt rheological tests and SEM.The research work is as follows:Firstly,the telechelic oligopropylene(PP-TVDs)with carbon-carbon double bonds were prepared by controlled thermal degradation of PP.Then the telechelic oligopropylenes(PP-TVDs)reacted with Cp2ZrHCl via hydrozirconation to prepare the metallocene catalyst,which was the initiator of ethylene polymerization reaction.After the metallocene catalyst being activated by methylaluminoxane(MAO)cocatalyst,the single peak appeared at the initial stage of the polymerization and then the peak gradually broadened at about 5 min.Ultimately,the single peak turned to two peaks with different intensity after 10 min.The introduction of ethylene gas would produce polypropylene-polyethylene block copolymers(bPE)and ethylene homopolymers(hPE).For the bPE-hPEs produced by ethylene coordination polymerization,Xc value of hPE was 73%,while the values of bPE-hPEs samples were smaller than hPE.Among them,the lowest one was 54.8%.Moreover,the tensile strength?elongation at break?Young's modulus of bPE was improved after the introduction of ethylene homopolymers.Utimately,the rheological behavior of bPE-hPEs was affected by bPE and the relaxation of bPE-hPEs shifted to low frequency region.The ?*value of bPE0.22-hPE0.78 was the highest,reaching 107Pa·s.In addition,bPE-hPEs could be used as a compatibilizing modifier to modify the physical and mechanical properties of industrial PP.bPE-hPEs was introduced to PP via solution blend to form PP/bPE-hPEs blends.The existence of bPE makes the interface between PP and hPE smooth than PP/hPE blends,which could achieve compatibilization effect.The tensile strength and elongation at break of PP/bPE-hPEs blends were higher than those of PP/hPE blends.The tensile strength and elongation at break of PP/bPE0.45-hPE0.55 samples reached 40.2MPa and 906%respectively.From the melt linear rheology results can be seen,on one hand,the existence of bPE in PP/bPE-hPEs blends increased the entanglement of molecular chain in the system and slowed down the movement of PP and hPE phases,so that the chain relaxation time was obviously lagged and the storage modulus G' was lower than the loss modulus G" in the low frequency region.On the other hand,the composite viscosity of PP/bPE-hPEs was much higher than that of PP/hPE blends,especially in the low frequency region,the ?*value of PP/bPE0.45-hPE0.55 samples reached 2.5×104Pa s,which improved the viscoelasticity of PP/bPE-hPEs blends.