Synthesis And Application Of Star-Shaped Ruthenium Olefin Metathesis Catalyst

Due to mild reaction conditions,high efficiency and controllability,olefin metathesis reaction has been widely used in the synthesis of small organic molecules and polymers.The development of various new ruthenium olefin metathesis catalysts has greatly promoted the application of olefin metathesis in varied fields.Among them,ring-opening metathesis polymerization is one of the powful tools to synthesize various complex structures and multifunctional polymers because of its high efficiency and controllability.In this article,a reactive trifunctional star-shaped ruthenium olefin metathesis catalyst was synthesized by designing a star-shaped ligand to coordinate with ruthenium,and a series of novel three-arm star functional polymers were obtained by ring-opening metathesis polymerization through the design of monomers.In addition,a biomass-based polymer is prepared by ROMP of a cyclooctene monomer with a biomass limonene derivative as a substituent.The details are listed as bellow:1.The Blechert’s catalyst,one of the powerful olefin metathesis catalysts in ring closing metathesis(RCM)due to its excellent initiation rate,is firstly demonstrated to show living ROMP towards conventional norbornene derivatives.The obtained homopolymers and block copolymers have very narrow PDIs and controlled molecular weights.The star-shaped styrene ligand is coordinated with ruthenium of the secondgeneration Grubbs catalyst to afford the trifunctional Blechert’s catalyst with high isolated yield,which was well-defined by NMR spectra.The trifunctional Blechert’s catalyst shows highly efficient activity in star polymerization of norbornene derivatives,including bulky fourth generation dendrons,to afford the tri-arm star polymers with precise molecular weight and narrow PDIs.The different solution property between the tri-arm star polymers and the linear polymers with similar molecular weight was studied by tandem GPC/light scattering.2.Norbornene macromonomers(MMs)with polystyrene(PS)or poly(tert-butyl acrylate)(PtB A)side chains were synthesized by a combination of atom-transfer radical polymerization(ATRP)and click reactions.A series of amphiphilic linear and starshaped brush block copolymers were obtained through sequential ring opening metathesis polymerization(ROMP)of MMs by the use of the highly active olefin metathesis Blechert’s catalyst and tri-functionalized Blechert’s catalyst respectively,followed by hydrolysis reaction.These well-defined diblock molecular brushes can undergo further self-assembly to form spherical micelles in solution,which have been characterized using DLS,AF4-MALLS,AFM,TEM and fluorescence spectra.The dynamic diameter increases as the hydrophilic backbone content increases for the vast majority of the linear and star copolymers.Brush-arm star diblock amphiphilic copolymers have smaller hydrodynamic diameter and aggregation number than the corresponding linear analogues.Moreover,the critical micelle concentration(CMC)values of star diblock copolymers show less sensitive to the variety of composition and more stable characteristics.3.Heterografted macromolecular brushes were highly grafted macromolecules with two different side chains attached to a norbornene monomer,consisting of a quantitative hydrophilic polyethylene glycol(PEO)graft and a hydrophobic polylactide(PLA)graft with different polymerization degrees.Using high-active Blechert’s catalyst and trifunctional Blechert’s catalyst to obtain linear and star-shaped amphiphilic double brush copolymers(DBCs)via ROMP.These polymers were characterized by tandem GPC/light scattering,and the results show that linear and starshaped double brush copolymers with narrow molecular weight distribution and controllable molecular weight were synthesized.DBCs can undergo intermolecular self-assembly in aqueous solution by DLS characterization,and the length of the PLA side chain and the length of the main chain of DBCs will affect the intermolecular selfassembly.According to TEM results,the DBCs micelles with composition structure have different morphologies in water,including three-dimensional membrane structure,vesicles and spheres.4.A new cyclooctene monomer with abundant biorenewable limonene oxide as the substituent group via simple esterification is presented,which could be polymerized by ring-opening metathesis polymerization(ROMP)using Hoveyda-Grubbs secondgeneration catalyst to afford polymer with remarkably high head-to-tail regioregularity and high trans-stereoregularity,as well as precisely placed ether branches on every eighth backbone carbon.Due to the presence of easily functional oxirane in limonene oxide side chain,the polymer can be efficiently modified with thiol to introduce rigid benzyl groups and secondary modified hydroxyl group through the nucleophilic reaction.Moreover,introducing dibutyl phosphate into the polymer to make it shows excellent flame retardant properties.The polymer even can bear pendent cyclic carbonate groups by CO2 insertion catalyzed with tetrabutylammonium bromide.In all cases,the main chains of the polymer remain intact.Differential scanning calorimetry(DSC),thermal gravimetric analyzer(TGA)and the microscale combustion calorimeter test(MCC)were used to study the thermal properties and flame retardancy.