Preparation Of Nano-objects By Polymerization Induced Self-assembly Based On RAFT Dispersion Polymerization And The Application

There is considerable interest in polymerization-induced self-assembly and reorganization(PISR)as a versatile and efficient route to fabricate various types of block copolymer nano-objects.The mechanism of PISR and the factors that affect the morphology of aggregates in PISR have been investigated in detail.While the expansion and application of the PISR system still need further study.In this dissertation,we prepare diblock copolymer nano-objects with various morphologies via PISR method,and the problem of low conversion in the classical alcoholic dispersion polymerization of St system is improved.The PISR method is combined with the photo-mediated polymerization to prepare the polymeric nano-objects at room temperature.Taking advantages of efictive fabrication of polymeric nano-objects via PISR,silica-based nanocontainer is fabricated for drug delivery.The main results are as follows:1.A novel nanocontainer,which has silica nanotube(SNT)core and pH-sensitive polymer shell attaching on the exterior surface of silica nanotube,is presented.Polymer nanorods,which are conveniently fabricated though polymerization-induced self-assembly and reorganization method,are used as templates for the deposition of silica to fabricate hybrid nanorods.Calcination of as-synthesized silica hybrid nanorods leads to hollow SNT.SNT is functionalized with RAFT agent,then surface RAFT polymerization is conducted to get PDEAEMA-b-POEGMA-coated SNT(SNT-PDEAEMA-b-POEGMA).Doxorubicin(DOX)can be encapsulated in SNT-PDEAEMA-b-POEGMA,and controlled release of loaded DOX is achieved by adjusting pH of the medium.In vitro cell viability and cellular internalization study confirm the potential application of this nanocontainer in drug and gene delivery.2.RAFT dispersion copolymerization of St and MMA is conducted in methanol using PHEA as a macro chain transfer agent(macro-CTA).Compared with the general macro-CTA mediated alcoholic dispersion polymerization of St,RAFT dispersion copolymerization of St and MMA can promote the morphology transition of di-block copolymer nano-objects.Three phase diagrams are constructed by changing the molar ratio of St/MMA to reflect the relationship between the degree of polymerization(DP)of P(St-co-MMA),solids concentration and morphology of obtained nano-materials,and it is found that the phase diagrams could be affected by the molar ratio of St/MMA.Ultra-sensitive differential scanning calorimetry(US-DSC)is employed to determine the glass transition temperature(Tg)of polymeric nanoobjects in methanol,and the result shows that the Tg values decrease with the increase of the molar content of MMA units in copolymers.Introduction of MMA units into the solvophobic block can enhance its mobility in methanol,which is beneficial for the morphology transition of di-block copolymer nanoobjects.3.A visible light mediated RAFT dispersion polymerization of BzMA is conducted in ethanol using PDMAEMA as a macro-chain transfer agent(macro-CTA),affording polymeric nanomaterials with various morphologies.Unlike the PISR process initiated by thermal stimuli,the photo-controlled PISR can be performed under more mild conditions,such as visible light and room temperature.Photoredox catalysis is employed to regulate the polymerization via a photo induced electron transfer(PET)process.It is observed that the polymerization can be affected by catalyst concentration and light intensity,and"ON/OFF" control over polymerization is also demonstrated4.RAFT dispersion copolymerization of St and NMAS is carried out in methanol using PI-IEA as a macro chain transfer agent(macro-CTA).Compared with the dispersion polymerization of St under same conditions,the rate of polymerization is accelerated when a little NMAS is introduced in the polymerization system,and the morphology transition of di-block copolymer nano-objects is promoted.Various nano-objects,including sphere micelles,nanowires and vesicles are observed.The intermediate state of lamellas and jellyfish-like nano-objects are formed during the transition from nanowires to vesicles.A series of polymer nano-objects are prepared by changing the solids content and the degree of polymerization of P(St-co-NMAS),and the phase diagram is constructed enabling the reproduction of targeted morphology of di-block copolymer nano-objects in large amounts.