Studies On The Ring-opening Polymerzation Of Rac-lactide And Carbonate Catalyzed By Bifunctional Squaramide Derived Organocatalysts

Polyester and polycarbonate materials are new types of green materials,which have attracted people's attention.Among them,polylactide is a research hotspot.Polylactide is a completely biodegradable plastic.With its excellent properties,it can be used as an ideal substitute for traditional polymer materials.It has been widely used in daily life.The three-dimensional structure of PLA affects its properties,and isotactic PLA shows excellent mechanical properties.At present,significant progress has been made in the research of metal-free catalysts for the ring-opening polymerization of racemic lactide,but the development of organic catalysts that can be used for the stereoselective ring-opening polymerization of racemic lactide at room temperature remain the main challenge.Therefore,the research and synthesis of catalysts with low toxicity,high activity and high stereoselectivity is still a problem to be solved.This dissertation mainly studies the synthesis of series of bifunctional squaraamide catalysts and the ring-opening polymerization of racemic lactide and cyclic carbonate.The main contents are as follows:1.The first part of the work used 3,5-bistrifluoromethyl-aniline and 1-adamantane as raw materials with different chiral amines to synthesize six bifunctional squaramid catalysts SQ-1?6.The structure was characterized by ¹H NMR and ¹³C NMR,and then preliminary experiments were carried out on the ring-opening polymerization of rac-LA to study the solvents and organic bases required for the reaction.2.The second part of the work uses squaraamide SQ-1 as a catalyst to study its catalyzed stereoselective ring-opening polymerization of racemic lactide.Through experiments,it is found that at room temperature,the bifunctional squaraamide catalyst SQ-1 can catalyze the stereoselective ring-opening polymerization of rac-LA to prepare polylactide with high stereoregularity(P_i^ESC up to 0.88)and controllable molecular weight.MALDI-TOF MS analysis shows that the chemical structure of the obtained PLA sample is well controllable without the side reaction of transesterification.3.The third part of the work studied the binary catalytic system consisting of squaraamide(SQ-2 to SQ-6)and 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU)Ring-opening polymerization of rac-LA at room temperature.Experiments have proved that the organic catalyst system composed of DBU and squaraamide derivatives is an effective catalyst for the stereoselective ring-opening polymerization of rac-LA.It has been proven that it can achieve high monomer conversion in a short reaction time and prepare molecular weight For polymers with a controlled up to 22.2 kg/mol and narrow molecular weight distribution((?)=1.10-1.24),the linear polymer structure and Bn O/H chain ends were verified by MALDI-TOF MS.Among them,during the polymerization process,the squaraamide SQ-2 with the most sterically hindered substituents showed the best stereoselectivity for the ring-opening polymerization of rac-LA,and there was no transesterification side reaction.4.In addition,the study of the squaraamide catalyst/organic base binary catalyst system on the ring-opening polymerization of cyclic carbonate 6CC has been studied.The experiment proves that the effect of the organic base TBD is better than that of CTPB.Polymers with higher selectivity(M_n^GPC=7.5 kg/mol,(?)=1.34,X_reg=0.72).