Aluminum Complexes Bearing Bidentate Amido-phosphine Ligands For Rop Of ?-CL

Polyesters and polycarbonates possess attractive characteristics including non-toxicity,renewability,degradability and biocompatibility,and thus have gained growing interest in both academia and industry.The selection and preparation of catalysts is the key for the synthesis of polyesters and polycarbonates.Alkyl aluminum catalysts have good controllability and phosphazene base catalysts has high catalytic activity,which have been widely concerned in the ring-opening polymerization?ROP?.In this thesis,the catalytic behavior of these two catalysts was studied.NMR,X-ray and elemental analysis were used to determine the molecular structure of the complex,while NMR,GPC,DSC and MALDI-TOF MS were used to determine the molecular structure and thermodynamic information of the polymer.The thesis mainly includes the following:The aluminum complexes Al1-5 have been synthesized and characterized for ring-opening polymerization of?-caprolactone.The molecular structures of Al2-4 were defined by X-ray diffraction studies,showing a distorted-tetrahedral geometry around the aluminum center in all structures.Careful comparison of these crystal structures suggested that different substituents on the ligands could lead to unignorable changed coordination environments around the Al center,thus affecting their catalytic properties.In the presence of BnOH,complexes Al1-5 efficiently catalyzed the ring-opening polymerization?ROP?of?-caprolactone??-CL?with high conversions in a controlled manner,and high molecular weights(M_n up to 118.6 kg mol^-1)of polycaprolactones?PCLs?were readily prepared.Immortal polymerizations by Al4 having bulky Ph₂CH groups were also studied with up to 20 equiv of alcohols and 2000 equiv of monomers,without sacrificing polymerization control.The long half-time of degradation and poor mechanical properties limit the practical applications of polycaprolactone.Copolymerization of different monomers is believed to be an attractive strategy to improve polymer properties.Ethylene carbonate?EC?,which has a five-membered ring,cannot achieve ring-opening homopolymerization owing to the unfavorable thermodynamics of its ring-opening reaction.EC can overcome the thermodynamic barrier when copolymerize to various cyclic esters,including?-caprolactone,?-valerolactone??-VL?and L-lactide?L-LA?.The random copolymerizations proceeded fast catalyzed by CTPB with a turnover frequency?TOF?of 19 800 h^-1 under mild polymerization conditions and afforded the corresponding copolymers without formation of the ether unit.The produced P?EC-co-CL?copolymers were characterized using ¹H NMR and ¹³C NMR.The results reveal the incorporations of EC?24–45 mol%?depend on the EC/CL ratios.With the same catalytic system and under similar conditions,the amounts of EC incorporated into EC/VL?up to26 mol%?and EC/L-LA?ca.4.8 mol%?copolymerizations were achieved.Polycarbonate/polyester copolymers with greater incorporation of EC were realized using a fast and selective process.