Study On Terpolymerization Of PO,CO₂ And The Third Monomer Catalyzed By SalenCoX

Carbon dioxide is a renewable and C1 resource that is abundant and cheap.The conversion of carbon dioxide covers the product from fuels to bulk and commodity chemicals,and even special products with biological activity.Coupling carbon dioxide with epoxides to produce polycarbonates and their derivatives is a good example.Carbon dioxide-based polycarbonate has good biocompatibility and biodegradability,and has potential application in many fields.Among them,polypropylene carbonate that can be produced from copolymerization of propylene oxide and carbon dioxide has attracted wide attention of researchers.The improvement of the thermal and mechanical properties of poly(propylene carbonate)and the functionalization of polycarbonate are currently hot research topics.In this study,SalenCoX(X=Cl,CN)catalysts were synthesized and characterized by NMR spectroscopy,electrospray ionization mass spectrometry and infrared spectroscopy.Dicyclopentadiene dioxide(EP1),1,2-Cyclohexanediol diglycidyl ether(EP2)were added into the copolymerization of carbon dioxide and propylene oxide as the third monomer.Both of the third monomers contain two epoxy groups and can undergo ring-opening copolymerization with CO2,which could link in the polymer chains and change the property of PPC in different ways.EP1 has a rigid structure with multiple rings,while EP2 has two arm branches containing a flexible group ether bond.The effects of different amount of third monomers added,reaction time,and temperature on the activity and selectivity of the catalyst,the molecular weight and its distribution of the polymer product,the content of carbonate units and the ratio of head to tailstructures were investaged.The thermal stability and rheological properties after polymer modification were also investigated.For both third monomers,the optimal reaction conditions for the polymerization were as follows:[PO]/[EP]/[Cat]/[PPNCl]= 2000/10/1/1,CO2 pressure was 2 MPa,the polymerization temperature was 50 ℃,and the polymerization time was 1 h.The two third monomers did not much affect on the activity and the selectivity of the catalyst that the product can maintain a high content of carbonate units and a head-to-tail structure.With EP1 as the third monomer,the molecular weight of the polymerization product decreased slightly.The molecular weight distribution broadened.The glass transition temperature reached a maximum of 40.02 ℃,and the thermal stability slightly reduced.The storage modulus G’ and the loss modulus G" were both increased,the viscosity also increased.For the case of EP2,the maximum molecular weight of the polymerization product reached 22.0 kg/mol,and the molecular weight distribution broadened significantly.It suggested that the EP2 was intergrated into the polymer chain and formed a "micro-crosslinking" structure.The maximum Tg of the polymerization product was 39.17 ℃,originating from the combined effects of the increase in molecular weight and the presence of flexible ether linkages in the polymer chain introduced by EP2.This study provides a reference for the optimization of polycarbonate property by using the third monomer with different properties.