Preparation Of Metalloporphyrins And Their Catalytic Properties For Ring Opening Polymerization Of Lactide

Metalloporphyrins not only have the advantages of easy preparation,but also have the characteristics of electron rich and large volume.They can be used as catalysts to catalyze the ring opening polymerization of lactide.Not only the polymerization can be controlled,but also the polylactic acid with certain stereoregularity can be prepared.In this paper,four series of aluminum compounds based on porphyrin derivatives were designed and synthesized,and they were used as catalysts for ring opening polymerization of lactide to obtain polylactic acid.The chemical structures of the pre-ligands and aluminum compounds based on porphyrins were characterized by ¹H NMR,¹³C NMR,IR and elemental analysis.The stereoselective ring opening polymerization of racemic lactide catalyzed by these aluminum porphyrins was discussed.The polymerization kinetics was studied and the mechanism of ring opening polymerization was explored.The specific work is as follows:1.Three tetraphenylporphyrin derivative pre-ligands and three tetraphenylporphyrin based aluminum compounds were prepared:methyl-5,10,15,20-tetraphenylporphyrin aluminum(compound 1),methyl-5,10,15,20-tetra(p-tert-butylphenyl)porphyrin aluminum(compound 2)and methyl-2,3,7,8,12,13,17,18-octamethyl-5,10,15,20-tetraphenylporphyrin aluminum(compound 3).The pre-ligands and aluminum compounds were characterized by¹H NMR,¹³C NMR,IR and elemental analysis.The catalytic properties of these aluminum compounds for the polymerization of lactide to polylactic acid were investigated.In the ring opening polymerization of racemic lactide,compound 3 showed high stereoselectivity and obtained isotactic polylactic acid.The kinetic data showed that both the monomer and the catalyst were first-order reaction kinetics for the polymerization initiated by aluminum compound 3.The NMR spectrum showed that the coordination insertion mechanism was used in the ring opening of lactide.2.Three porphyrin containing bis Schiff base pre-ligands and three corresponding porphyrin based bis Schiff base aluminum compounds were prepared and characterized:methyl-5,15-bis(4-phenylmethyleneamino)-10,20-diphenylporphyrin aluminum(compound4),methyl-5,15-bis(4-tert-butylphenylmethyleneamino)-10,20-diphenylporphyrin aluminum(compound 5)and methyl-5,15 bis(4-nitrophenylmethyleneamino)-10,20-diphenylporphyrin aluminum(compound 6).Compound 5 showed high stereoselectivity in the catalysis of racemic lactide and obtained isotactic poly(lactic acid)with the degree of isotacticity of 0.69.The kinetic study showed that both monomer and catalyst were first order reactions.The molecular weight distribution of the polymers is narrow,ranging from 1.10 to 1.26,which indicates that the ring opening polymerization of lactide can be controlled when the porphyrin based bis Schiff base aluminum compounds are used as catalysts.3.Three porphyrin based four Schiff base pre-ligands and corresponding three porphyrin based four Schiff base aluminum compounds were prepared and characterized:methyl-5,10,15,20-tetra(4-phenylmethyleneimino)porphyrin aluminum(compound 7),methyl-5,10,15,20-tetra(4-tert-butylphenylmethyleneimino)porphyrin aluminum(compound 8)and methyl-5,10,15,20 tetrakis(4-nitrophenylmethyleneamino)porphyrin aluminum(compound 9).Their catalytic properties for stereoselective polymerization of lactide were investigated.The ring opening polymerization of lactide catalyzed by aluminum compound 8 showed high stereoselectivity,and the isotactic poly(lactic acid)with Pm of 0.72 was obtained.The polymerization kinetics showed that the polymerization rate of aluminum porphyrin compound 8 was first order reaction kinetics with respect to the concentration of monomer and catalyst.4.A tetra-p-nitrophenyl porphyrin aluminum compound was prepared and characterized:5,10,15,20-tetra(4-(nitro)phenyl)porphyrin methyl aluminum,(compound10)and a copper porphyrin compound(Cu THMP).Compounds 1,2 and 10 catalyzed the polymerization of lactide in the presence of Cu THMP.The highest monomer conversion was 93.0%.The kinetic data showed that the polymerization rate of the system was first-order reaction kinetics with respect to the concentration of monomer and catalyst.Copper porphyrin based four arm star shaped polylactic acid has photocatalytic degradation of Rhodamine B in the presence of hydrogen peroxide.