Novel Metathesis Polymerization Approach Toward A New Family Of Metathesis Polymers With Multifunctionality

Grubbs’ ruthenium carbene catalyst could initiate ring-opening metathesis polymerization (ROMP) and acyclic diene metathesis (ADMET) polymerization effectively due to the versatile and well catalytic activity, good stability in air and the endurance of functional groups. Ruthenium-catalyzed olefin metathesis polymerization is an attractive and powerful tool to synthesize highly functionalized polymers, which has attracted considerable research attention recently in the field of polymer chemistry. This dissertation described the research work on obtaining a series of metathesis polymers with different structure and functionality via olefin metathesis polymerizations. Besides, as expected to explore new metathesis reactions, we originated a facile tandem ROMP and ADMET polymerization method to prepare long-chain highly branched polymers (LCHBPs) in one-pot procedure under certain conditions. These reactive LCHBPs could be effectively further functionalized to form unimolecular functional polymer nanoparticles and hybrid nanomaterials. The details are followed as:A combination of ROMP and click chemistry approach was utilized for the first time in preparation of multiblock copolymers. The dibromo-functionalized telechelic poly(butadiene)(PBD) was synthesized firstly by ROMP of1,5-cyclooctadiene in the presence of a symmetrical difunctional chain transfer agent and transformed into diazido-telechelic PBD, which was then reacted with a dialkynyl-containing azobenzene compound via click reaction, producing novel multiblock PBDs collected by azobenzene groups and newly formed triazole moieties. The monomer and polymer were characterized by FTIR, UV-vis, MS, and NMR techniques. The morphologies of multiblock PBDs were also investigated by AFM. The multiblock PBDs containing many azo groups and triazole moieties with or without hydrogen-bonding interreaction with4,4’-dihydroxybiphenyl molecule exhibited different photoisomerization efficiency from trans to cis as observation in UV-vis spectroscopy.Hyperbranched azo-polymer was successfully prepared through ADMET polymerization under conventional conditions based on a newly designed azo moiety-contained AB2monomer, which functionalized with one electron-rich terminal alkene, and two electron-poor acrylates. When treated with Grubbs’catalyst, electron-poor olefins do not homodimerize (or do so very slowly) but do participate in a secondary metathesis reaction with homodimers of more reactive olefins, that can be polymerized into a hyperbranched structure. The structure of hyperbranched azo-polymer was confirmed by IR, UV-vis, and NMR measurements. UV-vis spectra show that this kind of azobenzene-functionalized hyperbranched polymer could keep long photoactivated lifetime in cis form.A novel route to one-pot synthesis of LCHBPs was revealed by a tandem ROMP and ADMET polymerization procedure. A deliberately designed telechelic polymer bearing two electron-rich terminal allyloxy groups at the polymer chain ends and many electron-poor pendent acrylates along the polymer chain was synthesized by ROMP-CT, and then utilized as an A2B2n-type macromonomer in subsequent ADMET polymerization between allyloxy and acrylate triggered by Grubbs’catalyst, yielding finally the new type of LCHBPs. The structures and molecular weights of macromonomer and the resulting LCHBPs were characterized by NMR, MALD1-TOF MS and MALLS-GPC measurements. Moreover, different initiator combinations were selected for investigation of their propensity to initiating tandem ROMP-CT and ADMET polymerization, respectively. The different reactivity of initiators for various monomer architectures under appropriate reaction conditions were identified, and a series of LCHBPs containing acrylate and/or azobenzene groups were prepared in light of a controlled process.A benefit of these LCHBPs was that lots of pendent acrylate groups could be crosslinked covalently with the functional cross linker of dithiol or tetrathiol through thiol-Michael addition click reaction to actualize a controlled intramolecular crosslinking process, forming finially unimolecular functional polymer nanoparticles with finely tuning the number of thiol groups. GPC curves showed a shift to smaller hydrodynamic volume than that of uncrosslinked LCHBP, indicating that LCHBPs performed an intramolecular crosslinking reaction and formed the unimolecular polymer nanoparticles. These nanostructures take an approximately spherical shape, and well particle dispersion with no aggregated structures, as characterized by DLS, AFM, and TEM measurements. Furthermore, the effect of molecular weights and architectures of highly branched polymers upon the size of the unimolecular nanoparticles were also investigated.Utilizing these thiol-functionalized unimolecular polymer nanoparticles as template for the covalent attachment of Au nanoparticles on their surface, nanohybrids with the compact Au NPs arrays were readily obtained with high stability and marked difference in Au nanoparticle loadings, the more thiol group in polymer NPs is, the higher loading of Au nanoparticles on the surface of nanohybrids. The structures and optical properties of these nanostructures were characterized by FTIR, NMR, XPS, XRD, and UV-vis measurements. The morphologies of nanohybrids were investigated via DLS, AFM, TEM and cryo-TEM. The results revealed that hybrid nanostructures with various surface coverages of Au nanoparticles displayed unique morphology changes going through sphere, chainlike assembly, and nanorod as increasing the concentrations. Besides, the investigation of catalytic reaction showed that the hybrid nanomaterials could be used as a good recoverable catalyst for the reduction of nitro compounds with an excellent efficiency.