Stereoregular Polymerization Of Biomass-derived ?-methyl-?-methylene-?-butyrolactone

With the continuous depletion of fossil resources and the increasingly serious environmental problems such as the greenhouse effect,chemists have begun to work on the development of bio-based polymers to replace traditional petroleum-based polymers.The development of biomass-derived monomers that are simple and easy to synthesize and have excellent polymer properties after polymerization is the basis of research in this field.?-methyl-?-methylene-?-butyrolactone(?-MMBL)is derived from a bio-based platform molecular itaconic acid,the polymer of which has similar properties to poly(methyl methacrylate)(PMMA).The monomer can easily obtain the highly isotactic polymer through stereoselective polymerization.Since the highly isotactic polymer has excellent thermodynamic properties and solvent tolerance,the preparation of the highly isotactic polymer can further improve the performance of P_?MMBL.The development of efficient catalyst polymerization systems is another important research direction of producing bio-based polymers.Lewis pair polymerization(LPP),as an efficient,highly controllable,and chem-or regio-selective polymerization method,plays an important role in catalyzing the polymerization of polar olefins.Although LPP has developed rapidly and has many advantages,it still faces many problems to be solved.For example,the Lewis pair(LP)-catalyzed stereoselective polymerization has not yet been realized.Therefore,this paper selects?-MMBL as the monomer,hoping to develop a Lewis pair that can catalyze stereoselective polymerization,thereby obtain bio-based polymer materials with excellent properties.The specific research content is divided into the following two parts:In the first part,strong lewis acid organoaluminum and borane compounds are used as Lewis acid(LA),N-heterocyclic carbene and organophosphine are used as Lewis base(LB)firstly.Through regulating the structure of Lewis pair,optimizing the Lewis pair systems,which can efficiently catalyze the lewis pair polymerization of?-MMBL.The study found that the isotacticity(mm)of the polymer catalyzed by the Bis(2,6-di-tert-butyl-4-methylphenoxy)methylaluminum(MAD)/1,3-Di-tert-butylimidazole-2-idene(I^tBu)system was the highest,up to 78%.For the first time,the iso-rich atactic poly(?-methyl-?-methylene-?-butyrolactone)(P_?MMBL)catalyzed by the LP system under mild conditions was obtained.Mechanism studies show that it is an intermolecular Lewis pair polymerization mechanism.In the second part,the Zn(C₆F₅)₂/PCy₃ catalyst system was used to realize the high stereoselective polymerization of?-MMBL for the first time,and P_?MMBL with isotacticity of 93%was obtained.High-isotacticity P_?MMBL is a bio-based cyclic acrylate polymer material with excellent solvent tolerance and thermodynamic properties.Through the mechanism study,it is found that the high stereoselectivity is due to the fact that Zn(C₆F₅)₂ not only stabilizes the active center,but also activates another molecule of?-MMBL in the reaction,following the intramolecular Lewis pair polymerization mechanism,and leads to the steric hindrance interaction between the active center and the momomer enhanced.So it is inclined to stereoselective polymerization to obtain polymers of high isotacticity.In the end,P_?MMBL was successfully thermally depolymerized at 350°C for 0.5 h to obtain high-purity?-MMBL with a weight loss percentage of 95.4%,which was close to quantitative recovery,and a polymerization-depolymerization cycle was established.This also provides a strategy to recover monomers by thermal depolymerization for other bio-based polymer materials.