Synthesis Of Aliphatic Polyester/Polycarbonate Catalyzed By Aryl Phosphonium Functionalized Organoboron

Plastic products have become an indispensable part of people’s lives with their excellent performance,but the environmental problems caused by traditional petroleum-based plastics are becoming more and more serious.On one hand,it is a pollution problem caused by improper disposal of plastic waste.On the other hand,it is difficult to abandon such high-quality materials that bring great convenience to people’s lives.With the development of science and technology,the preparation of biodegradable plastics to replace the refractory petroleum-based plastics commonly used in people’s daily life has become an effective method to alleviate the problem of white pollution in current society.As a class of degradable polymer materials and partial replacement existing petroleum-based plastics with aliphatic polyesters and polycarbonates offer a more conducive pathway to the green and sustainable development of current society.In the past few decades,metal-based catalysts have flourished and made great contributions to the preparation of aliphatic CO₂-based polycarbonates.Compared with the limitations of metal-based catalytic systems,organic catalysts have sprung up in recent years,and have become a research hot-topic because of their advantages such as simple synthesis and no metal residues.In addition,compared with the pursuit of high activity and high molecular weight polymers,there are relatively few studies on low molecular weight polycarbonate diols（M_n<10 kg/mol）that can be used as raw materials for polyurethane industry.In addition,aliphatic polyester,as an excellent degradable material,can be prepared by ring-opening polymerization of epoxides and anhydrides.This polymerization method has the advantages of atomic economy,wide monomer source and high molecular weight control.However,the preparation of aliphatic polyester materials with narrow molecular weight distribution and well-defined terminal functional groups by organic catalytic system is still a challenge.Different from the previously reported bifunctional organic boron Lewis acid-base pair system as an initiator to realize the alternating copolymerization of epoxides and CO₂ to prepare polycarbonate or to initiate the alternating copolymerization of epoxides and anhydrides to prepare polyester,the purpose of this thesis is to design and synthesize a new type of bifunctional intramolecular P/B Lewis acid-base pair system,and to explore its application as a catalyst in the ring-opening copolymerization of CO₂ and epoxides,epoxides and anhydrides,especially under the condition of water as a chain transfer reagent.Finally,the preparation of low molecular weight polycarbonate diol with clear structure and aliphatic polyester with clear end functional groups is realized.The specific research content is divided into the following two parts:1.We developed a bifunctional intramolecular P/B Lewis acid-base pair synergistic catalyst.By integrating Lewis acid and Lewis base into one molecule,we transformed the two-component Lewis acid-base pair into a single-component Lewis acid-base pair,and successfully synthesized the catalyst PB1-PB8.In the second chapter,the bifunctionalized intramolecular P/B Lewis acid-base pair PB1-PB8 was used to catalyze the ring-opening copolymerization of CO₂ and cyclohexene oxide（CHO）to prepare poly（cyclohexene carbonate）（PCHC）.Firstly,the effects of carbon chain length and counter anions on the catalytic activity were studied.PB3 was found to act as a dual initiator and catalyst for CHO and CO₂ copolymerization in the presence or absence of water.Theα,ω-hydroxyl PCHC diol with clear structure can be prepared by introducing water as chain transfer agent into the catalyst PB8 with CF₃COO group as counter anion.The role of trifluoroacetic acid group in the polymerization process was studied in detail,and a reasonable mechanism was proposed.PCHC diols with different molecular weight（1.5 kg/mol-7.5 kg/mol）,low molecular weight distribution（（?）<1.2）and carbonate content（>99%）can be conveniently obtained by changing the amount of water and catalyst loading.The obtained low molecular weight PCHC diol can be used as a bifunctional macroinitiator for the ring-opening polymerization of L-lactide（L-LA）.The ABA-type triblock copolymer was prepared by one-pot method.2.In the third chapter,we used the bifunctionalized intramolecular P/B Lewis acid-base pairs as a synergistic catalyst to catalyze the ring-opening alternating copolymerization of anhydrides and epoxides.The microstructure of the obtained copolymers was elucidated by detailed MALDI-TOF-MS analysis.The experimental results show that both Br^-and 1,2-cyclohexanediol（CHD）in the polymerization can serve as initiators.The polymerization mechanism was further elucidated by kinetic studies and in situ ¹¹B{¹H}NMR experiments.The C5-bridged Lewis acid-base pair PB3 showed high activity(TOF=1920 h^-1),thermal stability（120℃）and good alternating selectivity（>92%）in the ring-opening polymerization of phthalic anhydride（PA）and cyclohexene oxide（CHO）.Under the feed ratio of CHO/PA/PB3=15000:10000:1,the catalyst PB3 achieved 96%conversion within 5 hours at 150℃.The M_nvalue of the high molecular weight fraction of the prepared P（PA-alt-CHO）was 51.8 kg mol^-1with（?）=1.10,and the lower molecular weight fraction wasattributed to Br^-initiated copolymerization.In addition,P（PA-alt-CHO）with a single peak distribution can be prepared by adding additional water as a chain transfer reagent.