One-Step Synthesis Of CO₂-Based Block Copolymer Via Synergistic Catalysis Of Organic Lewis Acid-base Pair

The development and application of plastics provides significant convenience for human life,however,the white pollution caused by overuse of traditional non-degradable polymers brings new challenges to human survival.Derived from copolymerization of the“green house”gas CO₂ and epoxides,CO₂-based polycarbontes show excellent biodegradability,biocompatibility as well as good barrier properties that are comparable to polyolefins.In this regard,CO₂-based polycarbontes may serve as ideal alternative for traditional non-degradable polymers and help solve white pollution.At present,the large-scale application of CO₂-based polycarbontes still faces the following problems:1)unsatisfactory mechanical or thermal properties;2)coloring problems and potential biological toxicity caused by residues of organometallic catalysts;3)higher production costs.To address these problems,this thesis focuses on facile synthesis of well-designed biodegradable block copolymers for fine-tailoring the properties of polyesters and polycarbonates via metal-free catalysis.Triethylboron(TEB)and 1,8-diazabicycloundec-7-ene(DBU)are used as inexpensive and readily available non-metallic two-component catalysts that can integrate chemoselective polymerization with kinetic controlled polymerization and enables one-step synthesis of CO₂-based block copolymers from mixtures of monomers.The main progress is as follows:The effects of catalyst ratio and CO₂ pressure on polymerization rate and selectivity have been investigated for tripolymerization of phthalic anhydride(PA),cyclohexene oxide(CHO)and CO₂ mediated by TEB/DBU pair.With TEB/DBU ratio of 1/1,alternating ring-opening copolymerization(ROCOP)of CHO/PA occurrd without insertion of CO₂,while the polymerization rate of CHO/PA ROCOP decreased with CO₂ pressure.When TEB/DBU=2/1,CHO/PA ROCOP and CHO/CO₂ ROCOP sequentially occured and tripolymerization displayed good chemoselectivity.Under optimized reaction condition of TEB:DBU:H₂O:PA:CHO=2:1:5:100:1000,CO₂pressure 2 MPa and 60?,one-step synthesis diblock poly(cyclohexene phthalate)-b-poly(cyclohexene carbonate)PCHPE-b-PCHC was achieved.Lactide(LA)was introduced into the CO₂ and CHO polymerization system,and the tricopolymerization reaction of CO₂,CHO and LA under the action of a two-component TEB/DBU catalyst was studied.The results show that LA had high polymerization activity in the system,and in a short period of time ring-opening polymerization(ROP)of LA completed.CO₂/CHO ROCOP entered the induction period,and generated cyclohexene carbonate(PCHC)in series.Increasing the ratio of TEB/DBU will inhibited the rate of LA ROP and increased the rate of CO₂/CHO ROCOP;increasing the pressure of CO₂ will reduce the reaction rate and form random copolymers.By adjusting the ratio of TEB/DBU and CO₂ pressure,under conditions of TEB:DBU:H₂O:LA:CHO=2:1:5:100:1000,CO₂ pressure of 2 MPa,and 60?,LA ROP and CO₂/CHO ROCOP with selective control,PLA-b-PCHC diblock polymer was synthesized in one step.The tetrapolymerization of PA,CHO,CO₂ and lactide(LA)was explored via cooperative catalysis of TEB and DBU.The experimental results revealed that higher TEB/DBU ration significantly improved the rates of both CHO/PA ROCOP and CHO/CO₂ ROCOP,but reduced the rate of ring-opening polymerization(ROP)of LA.Morever,higher CO₂ pressure is favorable for accelerating CHO/CO₂ ROCOP but slows both CHO/PA ROCOP and LA ROP.TEB/DBU catalytic system is resistant to water.Furthermore,kinetic controlled sequential LA ROP and CHO/CO₂ ROCOP is achieved while maintaining the chemo-selectively controlled CHO/PA ROCOP and CHO/CO₂ ROCOP via manipulating TEB/DBU ratio and CO₂ pressure.Under optimized reaction condition of TEB:DBU:H₂O:PA:LA:CHO=1.5:1:5:100:100:1000,CO₂ pressure 1 MPa and 60?,one-step synthesis triblock poly(cyclohexene phthalate)-b-polylactide-b-poly(cyclohexene carbonate)PCHPE-b-PLA-b-PCHC was achieved.