Study On The Preparation Of Poly (Propylene-co-1-butene) And Its Relationship Between Structure And Properties

Propylene copolymers with small amounts of 1-butene can greatly improve the properties of polypropylene material, such as low temperature toughness, printing performance, transparency, process ability and so on, leading to the expanding of its application. Poly (propylene-co-l-butene)s performance intensely relies on its composition and chain structure. The copolymerization catalyzed by Ziegler-Natta (Z-N) catalyst, which is a multi-active central system, resulted in copolymers with quite wide composition distribution. Thus well-distributed copolymers may be obtained by regulating active centrals through the improvement of catalyst structure. Copolymers are separately obtained from highly effective ball DQ (TiCl₄/MgCl₂/DIBP) catalyst and LiCl doped (TiCl₄/MgCl₂/LiCl/DNBP) catalyst.The copolymerizations used different main catalyst (as above), different comonomer ratios, the cocatalysts AlEt₃ (TEA), Al(i-Bu)₃ (TIBA) and external donors Diphenyl, dimethoxysilane (DDS), Dicyclopentyl dimethoxysilane (DCPDMS) are investigated. The analyses of microstructure of copolymers by using the graduation method, the fractions were characterized by ¹³C-NMR, FTIR, and DSC.The influence of different comonomer ratios on the copolymerizationon catalyzed by DQ catalyst had been investigated. It was found that the catalytic efficiency was higher than homopolymerization and increased along with the 1- butene mol% in the feed, gradually maximized and then dropped. As 1-butene mol% in the feed increased, the content of 1-butene in the poly (propylene-co-1-butene)s was heightened. When TIBA-DCPDMS used as cocatalyst system, the content of 1-butene in copolymers changed from 1.86 mol% to 18.72 mol% along the 1-butene in the feed changing from 5 mol% to 30 mol%. Copolymer samples were fractioned by n-hexane and n-heptane. The quantities of C₆S, C₇S enlarged along with the increasing of 1- butene ratio, but the content of C7I fraction gradually decreased. As the 1- butene mol% was fixed at 30, changing TEA and TIBA coordination proportion was 50/50, copolymerizations using two kinds of external donors caused lowest catalysis efficiency. Copolymerizations obtained a series of copolymers with higher 1-butene content thanseparately using TEA or TIBA as cocatalyst.When different LiCl doped (TiCl₄/MgCl₂/LiCl/DNBP) catalyst (0, 4.1 wt. %, 5.3 wt. %, 8.6 wt. %, 17.7 wt. %) were applied to propylene homopolymerization, it can be found that small amounts of doped catalyst produced polypropylene with two peaks in its molecule weight distribution curve, while the doping amount increased, two peaks changed to one again. The stereoregularity of polypropylene decreased a little.The LiCl doped (TiCl₄/MgCl₂/LiCl/DNBP) catalysts were then applied to propylene /1-butene copolymerization. The result indicated that several different doped quantities catalyst produced different amounts of 1 - butene units inserted in polypropylene chain. The content of 1- butene units in copolymer chains increased with the quantity of LiCl doped, and then got down. The contents of three fractions' of poly (propylene-co-1-butene) from different doped catalyst system are well-distributed.The influences of catalysts, cocatalysts, external donor for determining the concentration of the active sites in copolymerization of propylene/1-butene by DQ and TiCl₄/MgCl₂/LiCl/DNBP catalyst system were investigated in this thesis. The obtained results are helpful to the control copolymerization system to obtain copolymers with wonderful properties. It not only has important application prospect, but also could instruct the actual production.