Synthesis Of Water Soluble Macromolecular Photoinitiators And Its Application In RAFT Polymerization

Photopolymerization technology has been widely used because of its high polymerization rate,simple equipment,environmental protection and time/space controllability.As an important part of photopolymerization system,initiator has great influence on the polymerization speed and cost.At present,there are almost all small molecule photoinitiators in the market,but there are some obvious shortcomings in the residual small molecule photoinitiators after UV curing,such as strong odor,toxicity,yellowing and migration,which have a serious impact on the initiating effect and the apparent performance of the film,and limit its application scope.Studies have shown that the mobility of photoinitiators is related to their relative molecular weight,and the mobility of macromolecular photoinitiators decreases significantly.Reversible addition fragmentation chain transfer(RAFT)-regulated polymerization induced self-assembly(PISA)is a new method developed in recent years for the preparation of block copolymer nanoparticles.It can be used to prepare spherical,fibrous and vesicular block copolymer nanoparticles,and RAFT polymerization is also a method for the preparation of polymers with clear end groups.In this thesis,we report the synthesis of a variety of water-soluble macromolecular photoinitiators,and explore the efficient preparation of block copolymer nanoparticles by aqueous Pisa at room temperature.Furthermore,we further explore the influence of water-soluble macromolecular type I photoinitiators on aqueous PISA.The main contents are as follows:1.Polyethylene glycol monomethyl ether macromolecular photoinitiator(m PEG_n-TPO)with different molecular weights of acylphosphine oxygen was synthesized,and its structure and purity were characterized by ¹H NMR.The half-life of macromolecular photoinitiator m PEG_n-TPO was studied by UV-visible absorption spectroscopy.It was found that the half-life of m PEG_n-TPO decreased with the increase of molecular weight of macromolecular photoinitiator m PEG_n-TPO.Using m PEG₁₁₃-TPO as water-soluble photoinitiator,polyethylene glycol monomethyl ether methacrylate macromolecular RAFT reagent(PPEGMA₁₅-CDPA)and 2-hydroxypropyl methacrylate(HPMA)as nucleation monomer,aqueous RAFT dispersion polymerization was initiated at room temperature under visible light(?_max=405 nm,0.45 m W/cm²).Under visible light irradiation,the photo-initiated polymerization can achieve a high monomer conversion rate(>99%)within10 min,which is slower than the photo-initiated RAFT dispersion polymerization using small molecule photoinitiator 2,4,6-trimethylbenzoyl phenylphosphonate(TPO-Na).A series of block copolymer nanoparticles with different morphologies(spheres,worm,vesicles,etc.)were prepared by changing the reaction conditions,and then the block copolymer nanoparticles were prepared by aqueous raft dispersion polymerization with different molecular weight photoinitiators.TEM test showed that the morphology of block copolymer nanoparticles would not be affected by changing the molecular weight of macromolecular photoinitiators.2.SeveralTPO-functionalizedmacromolecularRAFTreagents TPO-PPEGMA_n-CDPA were synthesized and characterized by ¹H NMR,which proved that the photoinitiator TPO terminal group was coupled with PPEGMA.Based on the absorption spectrum difference between RAFT reagent and type I photoinitiator terminal group(TPO),green light(?_max=530 nm,10 m W/cm²)was used as the initiation light source to ensure that TPO did not decompose when RAFT aqueous dispersion polymerization using2-hydroxypropyl methacrylate(HPMA)as monomer,a series of TPO functionalized block copolymer nanoparticles with different morphologies(spheres,worms and vesicles.etc)were prepared by changing the reaction conditions.Due to the photoinitiation ability of TPO end groups,these TPO functionalized block copolymer nanoparticles were further functionalized by light in the presence of glycidyl methacrylate(Gly MA)or dimethoxyethyl methacrylate(DMAEMA).At the same time,due to the high initiating efficiency of TPO,these block copolymer nanoparticles have potential to be used as water-dispersible heterogenous photoinitiators for the preparation of hydrogels,the obtained hydrogels were resilient,soft,and tough.Properties and functionalities of these hydrogels could be further controlled by using different block copolymer nanoparticles.3.TPO-PPEGMA_10.8-CDPA was used as photoinitiator and RAFT reagent,Glycidyl methacrylate(Gly MA)is the nucleating monomer,visible light(?_max=405 nm,0.45m W/cm²)initiated RAFT emulsion polymerization at low temperature(25-50?).Under visible light irradiation,it only takes 20 min for the reaction to achieve high monomer conversion(>99%).Gel permeation chromatography(GPC)showed that M_ngradually increased during polymerization,and a good linear relationship with monomer conversion rate and low molecular weight distribution(M_w/M_n<1.41)showed that the polymerization process had good controllability.A series of block copolymer nanoparticles(spheres,worms,vesicles and large composite vesicles)with different morphologies were prepared by changing the reaction conditions.By turning on or off the light source to control the progress and stop of the polymerization,it shows that the photoinitiated RAFT polymerization is well controllable.The effects of reaction temperature on polymerization kinetics and morphology were studied in detail,and the phase diagram was constructed,it was found that RAFT emulsion polymerization initiated by redox reaction was different from that reported previously,the morphology of block copolymer nanoparticles prepared by visible light initiated RAFT emulsion polymerization using TPO-PPEGMA_10.8-CDPA as photoinitiator and RAFT reagent will change with the monomer concentration to some extent.