The Homopolymerization Of DTC And Copolymerization Of DTC With ε-caprolactone Catalyzed By Imidazolium-based Carbenes

1-isopropy-3-p-methoxyphenylimidazol-2-ylidene has been synth-esized and used to catalyze the polymerization of2,2-dimethyltrime-thylene carbonate (DTC) and the copolymerization of DTC withε-caprolactone (ε-CL) in the presence of benzyl alcohol (BnOH) as theinitiator in THF. And the polymerization conditions has been studied indetail, such as reaction time (t), the monomer concentration ([DTC] or[DTC]+[CL]), catalyst concentration([C]), reaction temperature (t),initiator concentration ([I]) as well as the ratio ([DTC]/[CL]) of thecomonomer of the copolymerization of DTC with ε-CL. Theexperimental results show the optimum conditions for DTCring-opening homopolymerization and the ring-openingcopolymerization of DTC with ε-CL. the reaction kinetics, thermo-dynamics of ring-opening homopolymerization and reactivity ratiosof the copolymerization of cyclic esters have been studied in detail.The structures of the polymers have been characterized and themechanism of the two polymerizations have been speculated by1HNMR,13C NMR and IR.The optimum conditions of the homopolymerization of DTC catalyzed by IopBnimy/BnOH system can be described as:[CL]=2.0mol/L,[DTC]/[C]=300(molar ratio),[CL]/[I]=200(molar ratio),15°C,15min, in THF. The experimental data shows that the IopBnimyis a potent organic catalyst for the ring-opening polymerization ofDTC. The polymers (PDTC) have heen produced by thepolymerization with high molecular weight (Mn=42,300g/mol),narrow polydispersities (PDI=1.49) and high conversion rate(98.2%). The kinetic studies indicate that the polymerization rate isfirst-order with respect to monomer and catalyst concentration.The overall activation energy of DTC polymerization initiated byIopBnimy/BnOH system amounts to29.42KJ/mol. The DSC curve ofPDTC shows a melting peak at115.4°C. the analysis of1H NMR andIR on the polymer demonstrates that the ring-openingpolymerization of DTC initiated by IopBnimy/BnOH system proceedsaccording to activated monomer mechanism with acyl-oxygen bondcleavage of the monomer.The experimental data shows that the optimum conditions forthe ring-opening copolymerization of DTC with ε-CL catalyzed byIopBnimy/BnOH system can be described as:[CL]:[DTC]=50:50infeed,[CL+DTC]=3.0mol/L,[CL+DTC]/[I]/[C]=500:2.5:1,25°C,30min,in THF. The copolymers (P(DTC-co-CL)) have heen produced by thecopolymerization with high molecular weight (Mn=36,600g/mol),narrow polydispersities (PDI=1.56) and high conversion rate(95.1%). Several copolymers with various feed ratios were quenchedat low comonomer conversions (10%-15%) and characterized by1HNMR. It can be seen the ring-opening polymerization of DTC will bemuch faster than ε-CL in the copolymerization. The ring-opening copolymerization of DTC with ε-CL via activated monomermechanism.