Ring-Opening Metathesis Polymerization Of Functionalized Cyclooctene And The Micellization Of Block Copolymers

Ring-opening metathesis polymerization (ROMP) is a widely used tool to synthesize well-defined and highly functionalized polymers, which has attracted considerable research attention recently in the field of polymer chemistry. Room temperature ionic liquids (RTILs), water, and supercritical CO₂ are considered as potential solvents for clean chemical processes and used widely in polymer synthesis. In this paper, we investigated the polymerization performances of functionalized cyclooctenes in ionic liquid [BMIm]PF6 and synthesized the block copolymers via ROMP in [BMIm]PF₆. The micellar characteristics of the block copolymer in selective solvent (THF) were investigated.The novel monomers of 5-substituted cyclooctene including 5-hydroxyl-1-cyclooctene (monomer 4) and 3-methyl-1-[acetyloxy-(5-cyclooctenyl)]-imidazol-1-ium tetrafluoroborate) (monomer 7) were first synthesized. The characterization of the synthesized monomer was carried out by ¹H NMR, ¹³C NMR, MS, and elemental analysis. In ¹H NMR spectroscopy, alkene protons signals of the cyclooctenyl ring appeared approximately at 5.5-5.7 ppm. Upon ring-opening and subsequent polymerization, these protons signals shifted upfield to approximately 5.38-5.39 ppm, this indicated the polymerization had occurred and the monomers had turned to be polymers. The obtained polymer was characterized via ¹HNMR spectroscopy and GPC. It was shown that the conversion of the monomer 4 was significantly higher when polymerization was carried out in ionic liquid compared to that in CH₂Cl₂, however, the conversion of charged monomer 7 performed in the ionic liquid reduced compared to that in CH₂Cl₂. The obtained polymers have markedly improved control over the molecular weights and polydispersities, which implied the higher initiation efficiency in [BMIm] PF₆.The kinetics of the initiation and propagation for ROMP of the charged monomer 7 catalyzed by Grubbs' catalyst [RuCl₂(PCy₃)(SIMes)(CHPh)] in [BMIm]PF₆ and CDCl₃ were measured by ¹H-NMR spectroscopy, respectively. The polymerization performances were much different in CDCl₃ and [BMIm] PF₆. Activation equation for the polymerization process in ionic liquid was also determined.Furthermore, a one-pot method was successfully used to synthesize block copolymers in [BMIm]PF₆. The prepared block copolymers can self-assemble spontaneously in THF to form polymeric micelles, which was confirmed by DLS, AFM, and TEMmeasurement.