Study On Preparation, Characterization And Properties Of Novel Hyperbranched Polyolefins

Polyethylenes(5 kinds) with different branching density and composition were synthesized usingα-diimine nickel complex/MAO catalyst system in the presence of ZnEt₂.In polymerization process,the branching density and composition of polyethylene were controlled by the competitive reaction of chain walking and chain transfer.Polyethylene with 140.0 branches per 1000 carbons was produced when Ni/Al/Zn =1/1000/0,and among these branches,88.5%was methyl.However,the branching density of the polyethylene prepared when Ni/Al/Zn =1/1000/200 decreased to 97.0 branches per 1000 carbons and the methyl percentage increased to 93.7%.By varying the MAO concentration inα-diimine nickel complex/MAO,polyethylenes(4 kinds) with different branching density were obtained.The results indicated that ZnEt₂ showed high capability for adjusting the branching density of resultant polyethylene.Furthermore,α-diirnine nickel complex/MAO/ZnEt₂ afforded higher activity thanα-diimine nickel complex/MAO for ethylene polymerization and it was possible that ZnEt₂ facilitated the reactivation ofα-diimine nickel complex.Seven samples of polyethylenes with different microstructures were produced usingα-diimine nickel complex/ansa-ethylenebis-(1-η⁵-indenyl) zirconium dichloride/MAO/ZnEt₂ alone from ethylene and the microstructures of resultant polymers indicated that the novel linear -hyperbranched multiblock polyethylene was successfully obtained.The possible mechanism was thatα-diimine nickel complex/MAO produced chain with hyperbranched architecture via chain walking,while ansa-ethylenebis-(1-η⁵-indenyl) zirconium dichloride/MAO afforded linear chain. Then chain transfer agent(ZnEt₂) facilitated chains shuttling between two kinds of active metal centres,as a result,the novel multiblock polyethylene was synthesized by chain shuttling polymerization.In addition,EPR signals of 16 types of the catalyst system suggested that excess MAO might undermine the activity of catalyst system,the possible reason was thatα-diimine nickel complex was distinctly reduced into Ni(I) by MAO and Ni(I) showed no activity in ethylene polymerization.Six kinds of hyperbranched-star poly[ethylene-co-2-(2-bromoisobutyryloxy) ethyl acrylate]- g-poly(tert-butyl methacrylate)[P(E-co-BIEA)-g-P^tB_uMA]with different molecular weight were prepared via the combining strategy of coordination polymerization and atom transfer radical polymerization,then cleaving P(E-co-BIEA)-g-P^tB_uMA afforded poly[ethylene-co-2-(2-bromoiso butyryloxy) ethyl acrylate]-g-poly(methacrylic acid)[P(E-co-BIEA)-g-PMAA].Mono-molecular micelles evidently formed in the P(E-co-BIEA)-g-PMAA solution using water as solvent and the reversible variation of the micelle size in the range of 30～80nm was exclusively attributed to variation of pH value of the polymer solution.Three kinds of hyperbranched-star poly[ethylene-co-2-(2-bromoisobutyryloxy) ethyl acrylate] -g-poly(ferrocenyloxy ethyl acrylate)([P(E-co-BIEA)-g-PFcEA]) with different PFcEA chain lengths were prepared via coordination polymerization and atom transfer radical polymerization. In addition,four kinds of hyperbranched poly(ethylene-co-ferrocenyloxy ethyl acrylate)[P(E-co-FcEA)] containing different FcEA content were synthesized with direct copolymerization of ethylene with FcEA.The investigation of P(E-co-BIEA)-g-PFcEA in CH₂Cl₂ via CV and UV-Vis indicated that P(E-co-BIEA)-g-PFcEA in CH2C12 was an appropriate receptor for anion recognition.Furthermore,a series of carbon nanomaterials were successfully synthesized with P(E-co-FcEA) as precursor via self-catalysis.The novel hyperbranched-star poly[ethylene-co-2-(2-bromoisobutyryloxy) ethyl acrylate]-g -poly(hydroxyl ethylacrylate)[P(E-co-BIEA)-g-PHEA]and poly[ethylene-co-2-(2-bromoiso butyryloxy) ethyl acrylate]-g-poly(hydroxyl ethylacrylate)-g-poly(ε-caprolactone)[P(E-co-BIEA) -g-PHEA-g-PCL]were successfully synthesized via coordination polymerization,atom transfer radical polymerization and ring-opening polymerization.The DSC curves and the polarized optical images of P(E-co-BIEA)-g-PHEA-g-PCL indicated that the crystal size of P(E-co-BIEA) -g-PHEA-g-PCL was much smaller than that of poly(ε-caprolactone).Furthermore,the rnicelles with the size of 50～200nm were effectively obtained from P(E-co-BIEA)-g-PHEA -g-PCL solution using ethanol as solvent.