Research On Novel Late Transition Metal Asymmetric Double Schiff-base Catalysts And Their Catalysis For Olefin Polymerization

As a kind of very important petrochemical products, polystyrene (PS), polymethyl methacrylate (PMMA) and methyl methacrylate-styrene copolymer (MS) are widely used in food packaging, medical apparatus, stationery, etc. for their good transparency and strength, and the optical properties. The performance of polymer depends on the microstructure, and one of the effective ways for the regulation of the microstructure of the polymers is to build appropriate structure of catalysts.Through the condensation reaction from aldehyde and amine and the coordination reaction from the late transition metal ions and the Schiff-base ligands, two series of20new asymmetric double Schiff base catalysts were obtained, respectively. They were characterized by element analysis (EA), infrared spectra (FT-IR), nuclear magnetic resonance (NMR), X-ray single-crystal diffraction (XRD), powder X-ray diffraction (PXRD) and thermogravi-metric analysis (TGA). All these catalysts were used for the polymerization of nonpolar monomer styrene (St) and polar monomer methyl methacrylate (MMA) as well as copolymerization of MMA and St after activated with azodiisobutyronitrile (AIBN) by solution polymerization. The relative molecular weight (Mn or Mw) and the relative molecular weight distribution (PDI) of the obtained polymers were determined by gel permeation chromatography (GPC). Furthermore, the microstructures of polymers were characterized by the FT-IR and1H NMR, and thermal stability was studied by TGA. Through the polymerization experiment, the relationship between the catalysts structures and the properties of polymers was analyzed. For a given catalyst, the influencing factors of the molar ratio of monomer and catalyst, polymerization temperature, polymerization time and the molar ratio of cocatalyst and catalyst were systematically investigated for the requirement of the controlled molecular weight size and the narrow molecular weight distribution.Firstly, the asymmetric Schiff base ligand OL or CL was synthesized through the condensation reaction of aldehyde and a single-NH2of diamine and then four new asymmetric Schiff base intermediates were obtained by the coordination of Cu+/Ni2+with the designed ligand. Furthermore, on the condition of suitable solvent and appropriate reaction temperature, salicylaldehyde,5-bromo-2-hydroxy-benzaldehyde,3,5-dibromo-2-hydroxy-benzaldehyde, o-vanillin or5-bromo-3-methoxy-2-hydroxy-benzaldehyde was added, and then20new asymmetric double Schiff-base catalysts, including OL-Cu catalysts system, OL-Ni catalysts system, CL-Cu catalysts system or CL-Ni catalysts system, were obtained respectively after appropriate reaction time.Secondly, the polymerization behaviors of nonpolar monomer styrene (St) were studied in detail by using OL-Cu/AIBN catalysts system, OL-Ni/AIBN catalysts system, CL-Cu/AIBN catalysts system or CL-Ni/AIBN catalysts system. The results showed that all catalysts have the medium activity for the polymerization of styrene, the Mn of PS is in the magnitude of103-104and PDI is between1.4-5.0. The activity of the catalysts is clearly influenced by the steric effects and the electronic effects of the catalysts:the electronic effects of the catalysts play an important role, and the input of electron withdrawing groups can increase the catalytic activity. The catalytic activity of nickel catalysts is about5times higher than that of copper catalysts in the same series catalysts. For the CL-Ni-5/AIBN catalyst system, when the condition of the molar ratio of monomers and catalyst of2000:1, the polymerization temperature of100℃, the polymerization time of6h and the molar ratio of catalyst and cocatalyst of1:2is selected, the activity is the highest (17.35×103g·mol-1h-1), the Mn of the polystyrene is the highest (41.417×103g·mol-1), and PDI is lower (1.43). These facts indicate that the polymerization can be controlled. Furthermore, the polymer is syndio-enriched atactic polystyrenes (82%).Thirdly, the polymerization behaviors of polar monomer methyl methacrylate (MMA) were also studied in detail by using OL-Cu/AIBN catalysts system, OL-Ni/AIBN catalysts system, CL-Cu/AIBN catalysts system or CL-Ni/AIBN catalysts system. The results showed that all catalysts have medium activity for the polymerization of MMA and the Mn of PMMA is in the magnitude of104and PDI is about2.0. The activity of the catalysts is clearly influenced by the steric effects and the electronic effects, and the electronic effects play an important role, and electron withdrawing groups can increase the catalytic activity. The catalytic activity of nickel catalysts is higher than that of copper catalysts in the same series catalysts. With the OL-Cu-5/AIBN catalyst system, when the conditions of the molar ratio of monomers and catalyst of1200:1, the polymerization temperature of90℃, the polymerization time of12h and the molar ratio of catalyst and cocatalyst of1:4are selected, the activity is the highest (16.640×103g·mol-1h-1), Mn=29.671×103g·mol-1and PDI=1.85. These facts indicate that the reaction can be controlled. Furthermore, the polymer is syndio-enriched atactic PMMA(61%).Finally, the copolymerization of polar monomer methyl methacrylate (MMA) and nonpolar monomer styrene (St) was investigated by using the OL-Cu/AIBN catalysts system and CL-Cu/AIBN catalysts system. The results showed that all catalysts are efficient for the copolymerization and the Mn of copolymer is about8000g·mol-1and PDI is about1.7. The activity of the catalysts is clearly influenced by the steric effects and the electronic effects, and the electronic effects play an important role, and electron withdrawing groups can increase the catalytic activity. The obtained copolymer is methyl methacrylate-styrene random copolymer.