Preparation Of Photoreactive Polymeric Microspheres By Photoinitiated RAFT Dispersion Polymerization

Micron-sized surface-functional polymeric microspheres have broad application in different fields such as charomatography,bioassay,optoelectronic devices etc and have attracted widespread attention in both industry and academia.The preparation of monodisperse polymeric microspheres with precise sizes and precise functional groups on the surface is an important direction in the field of polymer synthesis.Dispersion polymerization is one of the most commonly employed methods that can prepare monodisperse polymeric microspheres with diameters in the range of 0.5-15μm.Compared with thermally initiated polymerization,photoinitiated polymerization exhibits some significant advantages such as high polymerization rate and spatiotemporally light-controlled ability.Our group developed a facile method to prepare surface-functional polymeric microspheres by combining photoinitiated dispersion polymerization and reversible addition-fragmentation chain transfer（RAFT）polymerization.However,the number of functional groups on the surface of polymeric microspheres prepared by this method is low,which is difficult to increase by changing reaction conditions.To overcome this problem,this thesis would synthesize a series of photoreactive macro-RAFT agents and employed in visible light-initiated RAFT dispersion polymerization to prepare photoreactive polymeric microspheres.A series of surface-functional polymeric microspheres could be prepared by further photo-grafting on the surface.The main research contents are as follows:1.Monodisperse PMMA microspheres were prepared by photoinitiated RAFT dispersion polymerization in ethanol/water using a Z-type PEG macromolecular RAFT（macro-RAFT）agent.The RAFT group would be located on the surface of the obtained poly（methyl methacrylate）（PMMA）microspheres,which can be further surface-functionalized.The formation mechanism of microspheres was investigated by scanning electron microscope（SEM）.Effects of reaction conditions on the particle size and the particle size distribution of microspheres were studied.The results told that monodisperse microspheres could be obtained with 6～14 wt.%macro-RAFT agent.The concentration of photoinitiator had little effect on the particle size and particle size distribution of microspheres.The particle size of microspheres increased as increasing the monomer concentration.Moreover,the change in ethanol/water ratio also led to the change in the particle size of microspheres.2.A series of macro-RAFT agents containing UV photoinitiators were synthesized and employed in purple light-initiated RAFT dispersion polymerization for the preparation of PMMA microspheres with photoinitiators on the surface.Effects of reaction conditions on the particle size and particle size distribution of PMMA microspheres were investigated.~1H NMR results showed that the photoinitiator moiety still existed on the prepared PMMA microspheres,suggesting that the photoinitiator was stable during purple light-initiated RAFT dispersion polymerization.The kinetic study showed that a high polymerization rate was also observed with the monomer conversion being reached 95.8%within 90 min of purple light irradiation.PMMA microspheres with different surface functionalities were successfully prepared by surface-grafting of PMMA microspheres under UV light irradiation using various monomers.Finally,carboxyl-functionalized polymeric microspheres with an exceptional high number of carboxyl groups were successfully prepared by this technique,which permitted extensive surface bioconjugation of model proteins（e.g.streptavidin）.3.A block-type macro-RAFT agent containing moieties of a UV photoinitiator was synthesized and employed in purple light-initiated RAFT dispersion polymerization to prepare monodisperse poly（glycidyl methacrylate）（PGlyMA）microspheres.The formation process of PGlyMA microspheres was monitored by SEM.It was found that the particle size of the PGlyMA microspheres increased linearly with monomer conversion.Effects of the concentration of macro-RAFT agent,monomer concentration and initiator concentration on the particle size and particle size distribution of PGlyMA microspheres were studied in detail.Amine-functionalized PGlyMA microspheres were prepared by treating with ethylenediamine.Finally,polymeric microspheres with rough surfaces were prepared by photo-grafting PMMA on the amine-functionalized PGlyMA microspheres under UV light irradiation.