Ring-opening(Co)polymerization Of Lactones Catalyzed By Benzoheterocyclic Urea/MTBD

Aliphatic polyesters are a kind of recyclable,biocompatible,and degradable environmentally friendly materials,which have been used in biomedicine,food packaging,agricultural film,etc.Organic catalysts have received a lot of attention due to the advantages of green,low toxicity,low cost and easy availability.However,some existing organic catalysts exhibit the disadvantages,such as poor activity or insufficient controllability,which have limited the production capacity of aliphatic polyesters.It is of great significance to develop new high-efficiency organic catalytic systems to increase the production capacity of aliphatic polyesters and alleviate the increasingly severe environmental problems.In this thesis,a series of new and efficient catalysts have been developed to catalyze the ring-opening(co)polymerization of lactones.The main content of the thesis includes:(1)The benzoheterocyclic-urea catalysts were successfully synthesized by "one-pot method" at room temperature by the reaction between amino benzoheterocycle and isocyanate as raw materials.Their structures were characterized by EA,FT-IR,1H NMR,and 13C NMR to verify the accuracy of the catalysts structure.(2)A series of benzoheterocyclic urea catalysts containing N,O or S heteroatoms were very efficient for the ROP of ?-VL in combination with MTBD.Among these catalysts,the benzoxazolyl urea(NO)catalyst showed the highest activity and the existence of N-H group in heterocyclic rings was unfavorable for the ROP of ?-VL.The effect of catalyst concentration and reaction temperature on activity was explored,and the reaction conditions for NO/MTBD catalyzed ROP of ?-VL were optimized.Only 0.25 mol%of catalyst concentration can quickly catalyze the ROP of ?-VL and NO/MTBD have good activity at 25-60?.The ROP of different equivalents of ?-VL were processed at 25? using NO in combination with MTBD.When the molar ratio of[?-VL]0/[BnOH]0 changed in the range of 10-400,the produced PVLs had well-defined Mn and narrow D for each case.Both kinetic experiments and chain extension reaction verified the "living" characteristic under solvent-free conditions or in solution.A series of PVLs with different topological structures were also prepared by NO/MTBD catalytic system with different alcohols as the initiators and their properties were investigated by 1H NMR,GPC and DSC analysis.Without the addition of alcohol initiator,cyclic PVLs with Mn of 123.6 kg/mol and D of only 1.15 can be generated within 30 min.The possible reaction mechanism was proposed and predicted by NMR.In addition,the NO/MTBD system can also quickly catalyze the polymerization of ?-CL and L-LA with good controllibility.(3)The NO/MTBD system was used for solution ring-opening copolymerization of ?-VL and L-LA.The sequence structure of copolymers was analyzed by NMR and the randomness R of the polymer prepared under the pre-mixing of the raw materials was about 0.5,which was between completely random copolymerization and block copolymers.When the ratio of the two monomers was close,no melting peak could be observed and the sample was rubbery at room temperature as an amorphous polymer.As the VL segment decreased,the glass transition temperature of copolymers increased.In addition,the block copolymers PLLA-b-PVL were synthesized through the "one-pot method" and "chain extension method".The molecular sequence was controllable and the randomness R approached zero.The thermal properties were analyzed by DSC and compared with the random copolymers.It was found that when the two contents were close,the random copolymer did not have a melting point and only had a glass transition temperature;while the block copolymer PLLA-b-PVL had a melting peak at about 160?.