Controlled Synthesis Of Polymers With Various Topologies And Modification Of Mesoporous Silica Nanoparticles

It is well known that the properties of polymers are strongly influenced by their chain architecture. The design of macromolecules is important for obtaining the polymer materials with predetermined properties. Controlling polymer properties through design and synthesis of copolymers and macromolecular architectures is a challenging theme for polymer chemistry. For studying the relationship between the architecture and properties of polymers, and further designing the polymers with predetermined properties, it is necessary to apply known controlled living polymerization mechanism to synthesize different kinds of polymer with special architecture.Hyperbranched polymers are highly branched macromolecules with three-dimensional dentritic architecture, and they have many special physical and chemical properties, such as low viscosity, high fluidity, good solubility and a large number of terminal groups in comparison of linear polymers. The synthesis of hyperbranched polymers can be classified by two main strategies:(i) step-growth polycondensation of ABX monomers and (ii) self-condensing vinyl polymerization. Utilizing these polymerization strategies, a wide variety of hyperbranched architectures have been synthesized successfully, including hyperbranched polyesters, polyamides, polycarbonates and polyurethanes. Hyperbranched polymers have been utilized in various fields such as medicine carriers, nonlinear optics, nanometer materials and catalysis.Recently, block copolymers have attracted considerable attention because of their unique behaviors and potential applications, such as thermoplastics, surfactants, modifiers, dispersants, and tackifier, etc. With the development of living radical polymerizations, such as SFRP, ATRP and RAFT, a large number of novel well-defined block copolymers with controlled molecular weights and narrow molecular weight distributions were prepared.The nanoscale coupling of organic and inorganic materials has proven to be a very efficient way to create smart hybrid materials. Due to their highly ordered structure associated with large specific surface area, high internal volume, and narrow pore size distribution, mesoporous silica nanoparticles (MSNs) are ideal inorganic nanocarriers. The increasing interest in these materials is strongly evidenced by their biomedical applications devoted for instance to biocatalysis, bone tissue engineering, or to the creation of stimuli-responsive nanovalves for controlled drug delivery. Such hybrid organic-inorganic nanosystems can be advantageously created by coupling MSNs with polymers of controlled architecture and precise properties. As a facile method to synthesize polymer grafted MSNs, surface-initiated controlled free radical polymerization (SI-CRP) provides polymer brushes grafted MSNs.Based on the researches of the precursors, this dissertation described several outspread works in the synthesis of topologically structured polymers and the modification of mesoporous silica nanoparticles. All these facts are the origin and impetus of this thesis. The main results obtained in this thesis are as follows:1) To enhance the solubility of PPE and decreaseπ-πinteractions of PPE main chains, a facile synthetic strategy for preparation of a novel conjugated polymer with hyperbranched polymer side chains-PPE-g-HPBBEA has been developed through SCATRVP in one-pot. The molecular weight of PPE-g-HPBBEA increased with increasing feed ratio of BBEA to PPE-Br. The conjugated PPE backbones are wrapped with the HPBBEA, and this structure restrains the stacking of conjugated PPE chains because hyperbranched side chains decrease theπ-πinteractions of PPE main chains. Thus, the PPE-g-HPBBEA has good solubility in normal organic solvents such as THF and chloroform. The quantum yields of PPE-g-HPBBEAs increased significantly in comparison with their precursor, PPE-OH, and the quantum yields increased with the increase of molecular weight of the HPBBEA on the PPE backbones.2) Core-shell nanostructure with a mesoporous silica nanoparticle core and a hyperbranched polymer shell has been prepared by the surface-initiated SCATRVP of BBEA using MSN with bromoisobutyryl groups as initiator. The molecular weight of HPBBEA grafted increased with the increasing ratio of inimer BBEA to MSN-Br. Hybrid nanoparticles showed better dispersibility in organic solvents than the precursor MSNs. Utilizing MSN-g-HPBBEA as macroinitiator, PDMAEMA was successfully grafted onto the hyperbranched polymer shell of MSN-g-HPBBEA. The resultant nanoparticles, MSN-g-HPBBEA-g-PDMAEMA showed pH-responsive property, which will have potential applications in biomedicine and biotechnology.3) MSN-g-PMO core-shell nanoparticles were successfully synthesized through surface-initiating ATRP technique, and the inner channels of MSNs remained. The LCST of MSN-g-PMO could be adjusted by changing the feed molar ratio of MEO2MA and OEGMA. FITC as a model guest molecule could be encapsulated in the mesopores of MSNs above LCST, and released from the mesopores in MSN when the temperature was below LCST. Through an endocytic mechanism, MSN-g-PMO could easily carry FITC into cells. The MSN-g-PMO showed good biocompatibility and very low cytotoxicity, which make it a promising material for applications in biomarkers, biosensors and controlled drug delivery systems.4) In order to achieve RAFT polymerization of MEO2MA and OEGMA in the aqueous phase, at first, we synthesized macroRAFT agent PDMAa by utilizing ascorbic acid/tert-butyl hydrogen peroxide redox initiator and CMP as the RAFT agent, in aqueous solution at room temperature. The polymers obtained were characterized by GPC. MacroRAFT agent PDMAa could enhance solubility of MEO2MA in water, while control RAFT copolymerization of MEO2MA and OEGMA in water. The obtained ABA triblock polymer-PDMAa-PMO-PDMAa exhibit thermo-sensitivity and the LCSTs rise with the increase of OEGMA content in the PDMAa-PMO-PDMAa. The initiators in polymerization exhibit better biocompatibility, which has a special value in the field of biological materials. The triblock copolymers can form micelle in different temperature, and some insoluble molecules could enter into the core of micelles. The guest molecules in core of micelle could be released through dissociation of micelle in predetermined temperature. These properties make PDMAa-PMO-PDMAa be widely used in the field of drug delivery.5) We synthesized the PEO-b-PDMAEMA diblock copolymer by RAFT polymerization in aqueous solution at room temperature, and obtained the PEO-b-PDMAEMA-(MAH-p-CD) copolymer by the reaction of PEO-b-PDMAEMA and MAH-P-CD. The copolymers have excellent biocompatibility and low cell toxicity. We confirmed that the PEO-b-PDMAEMA-(MAH-β-CD) copolymer can transfect gene into the cell and successfully expressed the GFP gene. Through the cell experiment, we found that PEO-b-PDMAEMA-(MAH-β-CD) copolymer can cause cell autophagic behavior. These outstanding properties make PEO-b-PDMAEMA-(MAH-P-CD) copolymer be potential gene treatment materials which have a wide range of applications in the treatment of cancer.