Study On Ring Opening Polymerization Of Lactide Efficiently Catalyzed By Organic Catalyst

Aliphatic polyester materials are one kind of environmentally friendly polymer material.Polylactide(PLA)is one of aliphatic polyesters and has been extensively applied in many fields because of their good mechanical property,good biocompatibility and excellent biodegradability.Therefore,to develop novel efficient catalytic system and prepare PLA containing controlled structure becomes one hot topic in polymer synthesis.In this paper,a series of novel catalytic systems composed of organic catalysts with different topological alcohol initiators was researched in detail for the ring-opening polymerization(ROP)of L-lactide.The effects of polymerization conditions and the topologies of initiators on the ring opening polymerization activity of lactide and the topologies of polymers were systematically investigated by these novel organic catalytic systems.Meanwhile,the mechanism of ROP was carried on the preliminary exploration.The main results are as follows:1.The effect of polymerization conditions(monomer concentration,catalyst content,solvent types,polymerization temperature and time)and the topologies of initiators(monoalcohols,diols,triols and macromolecules alcohols)on the polymerization activity,molecular weight,molecular weight distribution and the topologies of polymers were investigated in detail via 1,8-diazabicyclo [5.4.0]undecano-7-ene(DBU)as catalyst and N-[3,5-bis(trifluoromethyl)phenyl]-N'cyclohexylthiourea(TU)as cocatalyst.The results showed that the efficient and controllable ring opening polymerization of lactide was realized by optimizing the amount of catalyst,the type of solvent,polymerization temperature and polymerization time.By regulating the steric hindrance,functional groups and topological structure of various alcohol initiators,polylactide containing diverse structures and functionalized end groups can be obtained.Using the reasonable matching between organic catalyst and alcohol initiator,the efficient and even "immortal" polymerization of lactide could be achieved for the first time for organic catalysts,which provided theoretical support and new synthetic route for the construction of topological degradable polyester materials.2.A series of novel macromolecular alcohols PVP-OH and PIP-OH were synthesized by free radical polymerization and reversible addition-fragmentation chain transfer polymerization(RAFT)with different unsaturated olefin monomers.Then,combing the “graft from” and ROP method,the amphiphilic copolymers with different grafting length and grafting density were synthesized by DBU/TU/macromolecular alcohols catalytic systems.Disappointedly,the polymerizations of lactide were not realized by this catalytic system,which might be attributed to the following three reasons: 1)strong hydrogen bonds were formed between the hydroxyl groups in the macromolecular initiators,resulting in the low content of free hydroxyl groups that can participate in the catalytic reaction;2)strong binding between hydroxyl group in the macromolecular initiator and water in the air,leading to the deactivation of the catalyst;3)The poor matching between organic small molecules and macromolecular initiators cannot effectively activate the initiators,resulting in the failure of ring opening polymerization.In this paper,a variety of functional and topological polylactide were synthesized efficiently by optimizing the polymerization conditions and regulating the topological initiators,which provides an efficient and simple synthetic route for ROP of lactide and laids a new theoretical foundation for expanding the application field of PLA.These research design and experimental results provide data support and guiding significance for the synthesis of polyesters via highly efficient catalytic ring opening polymerization of lactones.