Preparation And Characterization Of Nanoreactors Based On Grafted Polymers

Inorganic nanomaterials are widely applied in many fields such as light,electricity,biology and catalysis because of their unique properties.Throughout the development of nanotechnology,the design and preparation of nanomaterials is crucial.How to prepare nanomaterials with controlled size and shape by a simple and effective method has always been the research focus in the realm of nanotechnology.Researchers have prepared various nanomaterials by physical techniques such as ultraviolet infrared radiation,aerosol technology,photolithography,and hydrothermal methods,micro emulsions,etc.,although with their own shortcomings.In recent years,researchers have also developed a simple and economical process technology,namely polymer template method to produce nanomaterials with controllable and stable dispersion of size and morphology.The key to this technique is to introduce functional groups onto one segment of the block polymer to provide orientation sites for nucleation and growth of the nanoparticles,and the another segment acts as a capping ligand to prevent aggregation of the nanoparticles.It is endowed with excellent controllability and exceptional stability.Generally,the polymer template can be present as a single molecule or as a self-assembled micelle.In this work,based on the graft copolymers,we have attempted to prepare a series of novel single-molecule or micellar nanoreactors.The main results are as follows:（1）Study on single-molecule nanoreactor based on hyperbranched polyglycidyl（HPG）graft polymerFirst,the HPG was synthesized by ring-opening polymerization（ROP）of glycidyl（Gly）monomer,and the atom transfer radical polymerization（ATRP）macro-initiator（HPG-Br）was prepared by esterification of hydroxyl groups on HPG with 2-bromoisobutyryl bromide.Then,the poly（t-butyl acrylate）（Pt BA）and polymethyl acrylate（PMA）blocks were sequentially introduced onto HPG by ATRP method,and the graft polymer HPG-g-（PtBA-b-PMA）was obtained.The PtBA block was selectively hydrolyzed by trifluoroacetic acid and the polyacrylic acid（PAA）segment was generated,which produce the HPG-based amphiphilic graft copolymer HPG-g-（PAA-b-PMA）.The results of nuclear magnetic resonance（¹H NMR）,gel permeation chromatography（GPC）and differential scanning calorimetry（DSC）showed that HPG-g-（PAA-b-PMA）was successfully synthesized.Finally,using ferrous chloride（FeCl₂）/ferric chloride（FeCl₃）or silver nitrate（AgNO₃）as precursors,the metal ions was incorporated onto carboxyl groups on the PAA segment and in-situ reduced for magnetic ferroferric oxide（Fe₃O₄）and silver（Ag）nanoparticles.The transmission electron microscopy（TEM）measurement showed that the obtained magnetic Fe₃O₄ nanoparticles have an average diameter of 12 nm and nano-Ag particles have an average diameter of 15 nm.The diameters measured by dynamic light scattering（DLS）was slightly larger than those by the TEM measurement.The PMA segment coated by the periphery of the nanoparticle could contribute the increasing of the hydrodynamic radius of nanoparticles,further demonstrating that the nanoreactor was successfully prepared.（2）Study on single-molecule nanoreactor based on polyglycidyl methacrylate（PGMA）graft polymerFirst,the PGMA with narrow molecular weight distribution was synthesized by ATRP,and three hydroxyl groups were introduced on each GMA unit by the ring opening reaction of the thiol glycerol with the epoxy groups on PGMA.The macroinitiator PGMA-Br with three grafting sits on each GMA units was obtained by the esterification of hydroxyl groups with 2-bromoisobutyryl bromide.Then,the PtBA and PMA segments were sequentially introduced on the PGMA backbone to give the graft polymer PGMA-g-（PtBA-b-PMA）,which was further selectively hydrolyzed by trifluoroacetic acid to give graft copolymer PGMA-g-（PAA-b-PMA）.The structure and composition of the obtained graft polymer were characterized using GPC,¹H NMR,and DSC measurements.Similarly,the magnetic Fe₃O₄ nanowires were prepared by FeCl₂/FeCl₃ precursors,and the morphology of the nanoparticles was characterized by TEM and DLS measurements.（3）Study on micellar nanoreactor based on PGMA graft polymerBased on the research on the above-mentioned single-molecule graft copolymer nanoreactor,the micellar nano-reactor based on PGMA graft polymer was also attempted.First,using a ring opening reaction of dodecyl mercaptan(C₁₂H₂₅SH)with an epoxy group on PGMA,the dodecyl group was introduced.The introduced hydroxyl group was further esterified with 2-bromoisobutyryl bromide esterification reaction.Subsequently,the hydrophilic carboxyl groups were introduced by a reaction between bromine and mercaptopropionic acid and the graft copolymer PGMA-g-C₁₂/COOH was generated.Alternatively,the PtBA segment was introduced by ATRP of tBA monomer and aimed to graft copolymer PGMA-g-C₁₂/PtBA.The PtBA segment was also selectively hydrolyzed by trifluoroacetic acid to give graft copolymer PGMA-g-C₁₂/PAA.Both of the prepared PGMA-g-C₁₂/COOH and PGMA-g-C₁₂/PAA have amphiphilic characteristics and are expected to form a micellar nanoreactor by self-assembly.The structure and composition of the grafted product were characterized by ¹H NMR,DSC and thermogravimetric analysis（TGA）measurements.The results gave solids evidence that the graft copolymer was successfully synthesized.In summary,we have successfully synthesized a series of single-molecule nanoreactor and the micellar nanoreactor based on HPG and PGMA graft copolymers using the post-modification technology,ROP and ATRP techniques.The application of these polymer templates were preliminarily exemplified for Fe₃O₄ and Ag nano nanoparticles.The progress in this thesis is expected to provide theoretical basis and guidance for the versatile preparation and wide application of novel nanomaterials.