| Polyolefin materials take the biggest share of global plastic market, duo to the widely available raw materials and high cost performance. Thereinto, ethylene/a-olefin copolymers, such as linear low density polyethylene (LLDPE) and polyolefin elastomer (POE), with excellent properties, are very popular in the market. China is a latecomer to the development of polyolefin industry, and cannot produce POE so far. And a significant portion of the LLDPE is 1-butene based copolymer with lower performance. Therefore, it is urgent to improve the present production technology of LLDPE and develop the production technology of POE with China’s own intellectual property.Tandem catalysis technology applies one reactor, uses ethylene as the only feedstock, generates the comonomer (high a-olefin) in situ with oligomerization catalyst, and makes copolymerization happen with copolymerization catalyst. In comparison to traditional polymerization process, it has a great cost saving in comonomer production, transportation and storage. Many tandem catalysts system were reported, however, most of them did not focus on the present industrial equipments and conditions for the production of ethylene/a-olefin copolymers. Polyethylene byproducts were also easily produced by a lot of the oligomerization catalysts applied.In this thesis, based on SNS-Cr as the ethylene trimerization catalyst, which had high activity, high selectivity and very low amount of polyethylene byproduct, we tried to combine it and supported Z-N catalyst with mixed co-catalysts of TEA and MAO, to prepare 1-hexene based LLDPE with well kept partical morphologies. With low amount of co-catalyst, SNS-Cr exhibited high activity and high trimerization selectivity. In comparison to the run of ethylene homopolymerization, the tandem catalytic polymerization had slightly higher activity, and the molecular weight of polymer product could be adjusted by varying the ratio of the two catalysts. The molecular weight of the resultant copolymer decreased with increasing the usage of SNS-Cr, and the melting point also decreased slightly. The crystallinities of products ranged in 50-60%, belonging to the feature of commercial LLDPEs. The adhesions of subparticles became more severe when the 1-hexene content in the polymer was increased, but 1-hexene based LLDPE with a melting point of 122.3℃ still kept good particle morphology without obvious agglomeration of particles. This tandem catalysis system is applicable for the present industrial equipments and meaningful to guide the development of slurry polymerization process.Furthermore, the ethylene trimerization catalyst SNS-Cr was combined with constrained geometry catalyst (CGC-Ti) that had high activity and high copolymerization ability under high temperature, using MAO as co-catalyst, to develop another tandem catalysis system. The runs under 75℃ and atmospheric pressure were firstly investigated. Ethylene/1-hexene copolymers ranged from semi-crystallite to completely amorphous could be prepared. The highest 1-hexene content in the copolymer could reach 14.9 mol%. Then the runs under 110℃ and high pressure were carried out. It was found that SNS-Cr still had high selectivity in 1-hexene and high activity, and the amount of PE byproduct was quite low.The resultant copolymer had a 1-hexene content of 3.1 mol% and exhited the feature of thermal plastic elastomer. It had close mechanical properties to commercial POE samples. A mathematical model, describing the kinetics of tandem catalysts system of SNS-Cr and metallocenes, in CSTR for preparation of ethylene/1-hexene copolymers, was developed. The simulation results showed that pre-trimerization could shorten the transition term. Increasing the [Cr]in/[M]in ratio could improve the comonomer content in copolymer, but lower the molecular weight. Raising the ethylene pressure could solve this problem. This tandem catalysts system has good stability. After several reaction condition switches, the system could reach stability again.Based on the recent progress in olefin living coordination polymerization, two new fluorinated FI-Ti catalysts, PFI and AFI, were synthesized. The NMR and XRD analysis could clearly and definitely describe their structures. PFI is a homogeneous catalyst, and AFI is a self-immobilized catalyst. PFI and AFI had good livingness of ethylene polymerization. AFI had faster chain propogation rate than PFI. Self-immobilization would induce chain transfer reaction, broadening the MWD. Then the living copolymerization of ethylene and 1-hexene with PFI was investigated. PFI had good potential in preparation of UHMW ethylene/1-hexene copolymers. The resultant copolymer had Mw> 1.4×106 g/mol, F2> 25 mol% and PDI< 1.5. The molecular weight could continue increasing by extending the polymerization time. In comparison to commercial 1-octene based POE, the UHMW ethylene/1-hexene copolymers exhibited higher modulus and recovery properties. The completely amorphous copolymer had an elongation of>1700% without break, and its glass transition temperature could reach-61℃, also comparable with commercial POE. The reactivity ratios were r1～47, r2～0.02, and the product of reactivity ratios was very close to 1, indicating random unit distribution. PFI had comparative copolymer ability with many metallocene catalysts. Based on a developed kinetics model, the true kinetic parameters of PFI in ethylene/1-hexene copolymerization in toluene at 50℃ were calculated::ki1=0.376±0.008,kp11=3920±933, kp12=83.9, kp21=30.5 kp22=0.671±0.006 (unit: L·mol-1·s-1). The predictive results could match the experimental results very well.At last, a novel tandem living catalysts system of SNS-Cr/PFI/dMAO was firstly developed. Under 50℃, with 12 min polymerization, the resultant LLDPE could have molecular weight close to 1 million g/mol. Extending the polymerization time would make a higher molecular weight. However, with a relatively high usage of SNS-Cr, the resultant copolymers were still LLDPEs. |
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