Research On Synthesis And Thermal Stability Of Polycarbonate By Copolymerization Of CO₂ Under Cocatalyst Supported Double Metal Cyanide Catalysts

In recent years,to solve the environmental problems caused by carbon dioxide?CO₂?,the research and development of carbon dioxide polymer has been a hotspot in the green comprehensive utilization area of CO₂.The key factor restricting the CO₂ and heterocyclic molecules?such as epoxy compounds,cyclic nitrogen derivatives,epithio compounds,etc.?polymerization is the catalyst in the polymerization process.Among the developed catalyst systems,double metal cyanide?DMC?complexes are well-known heterogeneous catalysts for the effective utilization of CO₂ to prepare polycarbonates.But the catalytic activity of the catalyst is relatively low and the thermal stability of the polymer product is poor.With an objective of improving the catalytic activity of DMC,the paper is committed to introduce four different co-catalysts to the DMC catalyst for the copolymerization of CO₂ and epoxy compounds.Zn-Fe???DMC and Zn-Co???DMC catalysts were synthesized by ball milling using ZnCl₂/ZnBr₂ and K₃Fe?CN?₆/K₃Co?CN?₆.Subsequently,poly propylene carbonate?PPC?were prepared by Zn-Fe???DMC/Zn-Co???DMC with different proportions of ?-Al₂O₃ as co-catalyst.The structure and thermal stability of PPC were characterized by FTIR,1H-NMR,13C-NMR,GPC,TGA and DTG.The results show that DMC with ?-Al₂O₃ can improve catalytic performance,and enhance the thermal stability of PPC.GPC analysis indicate the average molecular weight?Mn?of PPC is up to 8,873,and the molecular weight distribution PDI is 1.55,TON?turn-over-number?is 321.83.The resultant thermogravimetric analysis curves show that the maximum decomposition temperature Tmax of PPC is up to 329.3 ?.The copolymerization of CO₂ and PO,as well as the tercopolymerization of CO₂,PO and lactone??-butyrolactone/?-ester?/anhydride?methyl nadic anhydride and NA-anhydride?was polymerized by Zn-Fe???DMC supported with co-catalyst nano-SiO₂.The structure and thermal stability of the polymer products were characterized by FTIR,1H-NMR,13C-NMR,GPC,TGA and DTG.The results show that DMC with nano-SiO₂ can improve catalytic performance,and enhance the thermal stability of products.GPC analysis indicate the average molecular weight of PPC is 2.3⁶.3K and the molecular weight distribution is 1.06¹.25.The introduction of the third monomer can effectively improve the structure and thermal stability of the polymer products.GPC analysis also show that the average molecular weight of the ternary polymer is 2.3⁵.0K,and the PDI is 1.06⁵.11.And TGA curves indicate that the maximum decomposition temperature Tmax of products is up to 384.7 ? and the thermal decomposition temperature of T50% is up 344.2?.Zn-Fe???DMC catalysts were synthesized by ball milling with adding four different cocatalyst surfactants,dodecyltrimethylammonium bromide?DTAB?,cetyltrimethylammonium bromide?HTAB?,tetrabutyl bromide?TBAB?and tetrabutylammonium fluoride?TBAF?.The CO₂,PO and 3,3',4,4'-benzophenone tetracarboxylic dianhydride?BTDA?tercopolymerization was catalyzed by Zn-Fe???DMC with different surfactants as co-catalyst.Its average molecular weight of PPC is 3.4 to 4.2K,PDI is 1.17 to1.20.The catalytic activity of cocatalyst TBAF was the highest,which TOF?turn-over-frequency?,Mn and PDI is10.69,4084,and 1.19,respectively.With the surfactant TBAB as the co-catalyst,the maximum thermal decomposition temperature of ppc is up to 375.2?.The tercopolymerization of CO₂,PO and succinic anhydride?SA?/phthalic anhydride?PA?was catalyzed with Zn-Fe???DMC with graphene oxide?GO?as a cocatalyst.The polymer has a number average molecular weight of 3.2⁵.9K,a PDI of 1.04².73,and TOF is 14.51.The catalytic activity of the catalyst and the thermal stability of the polymerization product can be effectively improved by using GO as the cocatalyst.When the DMAP and EDC were added in different ways,the thermal stability of the polymeric material was further increased and the maximum pyrolysis temperature was up to 363.1°C.The addition of different cocatalysts to DMC catalyst not only can effectively improve the catalytic activity,but also improve the thermal stability of the polymer.Thereby,employing co-catalysts to the DMC catalyst provides a new approach for the copolymerization of CO₂ and epoxy compounds.