Study On The Synthesis Of PE In-situ Alloys By Gas-phase And The Relationship Between Its Properties And Structure

The first PE/PP and PE/PP/EPR in-situ alloys were synthesized by spherical Ziegler-Natta catalyst in gas-phase.The polymerization process consists of three or four stages: the first stage is pre-polymerization, the second stage is gas-phase ethylene homo-polymerization, and the third stage is gas-phase propylene homo-polymerization, if necessary the fourth stage is co-polymerization of ethylene and propylene. The alloy ?particles, which are big with narrow diameter distribution, have good morphology and large hole. They have special phase morphology and chain structure. That results in excellent mechanical properties.Firstly the pre-polymerization technique was systematically investigated under different conditions. The best condition of pre-polymerization fit for synthesizing spherical PE granule was found.The kinetics of homo-polymerization of ethylene has been investigated thoroughly. The influence of polymerization temperature, monomer pressure and consumption of H2 on the kinetics were studied. And the mechanism of particle growth was disclosed.The conditions of synthesizing PE/PP and PE/PP/EPR alloys were optimized. Under these conditions a series of PE/PP and PE/PP/EPR in-situ alloys were synthesized directly in the reactor. The content of propylene of PE/PP alloys can be changed in the field of 6~65mol%. And that of PE/PP/EPR alloys is in the field of 33~42mol%.All of the PE/PP alloys and PE/PP/EPR alloys possess excellent mechanical properties; it shows that synthesizing alloys in-reactor can evidently improve the mechanical properties of polyolefin materials. PE/PP alloys and PE/PP/EPR alloys have not only high impact strength but high flexural modulus. For example, the impact strength of the PE/PP alloys which contains 73.9wt% propylene is 90. 2 kJ/m2 and its flexural modulus is2633. 5 MPa; the impact strength of the PE/PP/EPR alloys which contains 49.4wt% propylene is 160.3 kJ/m2 and its flexural modulus is as high as 3235.8 MPa. The mechanical properties of these two kinds of alloys are almost similar to some engineering plastics and better than the other materials based on PP and PE.Characterized by IR, DSC and 13C-NMR, it shows that the PE/PP alloys and PE/PP/EPR alloys comprise multiple fractions that are different in composition and chain sequence structure. It is clear that the alloys are made up of five portions: ethylene-propylene random copolymer, multi-block ethylene-propylene copolymer,PE-PP bi-block copolymer, PE and PP. The main section of the alloys is PE-PP bi-block copolymer. For example, the content of PE-PP bi-block copolymer in PE/PP alloys is in the field of 25. 4-67.0wt%; the content of PE-PP bi-block copolymer in PE/PP/EPR alloys is near 50wt%. Abound of PE-PP bi-block copolymer results in good compatibility between PP, PE and EPR. The characterization results show the compatibility between continuous phase and dispersed phase of the alloys is good.To expand the utility of polyethylene alloy, we modified the alloys by solid graft co-polymerization with polar monomer, for example MMA to improve its adhesion, printing, and dyeablity. For high porosity as much as 49.9wt%, the grafting degree of PE/PP alloy was 42wt% synthesized with appropriate condition and it could be controlled in the field of 0~42wt%. By TGEF, FT-IR, PLM, DSC and 13C-NMR, the modified PE/PP alloy was fractionated and characterized. It found that PMMA is mainly grafted no the chain of PP.Finally, the chain structure and phase morphology of PP in-situ alloys (PP/PE alloys and PP/EPR alloys) have been studied. Compared with PE in-situ alloys, there are resemblance and difference between PP in-situ alloys and PE in-situ alloys. They are all mainly made up of three portions: ethylene-propylene random copolymer, multi-block ethylene-propylene copolymer and PE-PP bi-block copolymer. But the distribution of these compositions is different to each other.