| Photopolymerization is green technology, applied to a wide range oftemperatures, with strong superiority in biological applications andpolymerization of monomers which are sensitive to temperature.Photopolymerization is highly efficient and green, with a great practicalvalue. In the recent20years, academics realm have recognized thatcontrolled/living radical polymerization (LRP) is the superior method forthe synthesis of structurally well-defined polymeric materials withwell-controlled molecular weights and molecular weight dispersity undermild conditions, and it has very improtant practical significance forscientific research. Now, the reported living radical polymerizationsystems by light are very scarce, mainly because the lack of appropriatephotographic group used to adjust activating polymerization process, andthe existing systems can not be without the transition metal as a catalyst,or use colored relish chain transfer agent to control the polymerization.This paper studies Cycloketyl Midiated living radical polymerization,whicn can control polymerization well under mild conditions, and itdoesn't need any transition metal. This method presents importantpotential for practical large-scale production of industrial polymers. Themain content is as follow:By1H NMR, IR, MS and UV, we observe that the ratio of hydrogens at benzene ring and the hydroxyl is2:1, consistent with the structure ofBIXAN formula. And we confirm the purity of BIXAN initiator is above95%by HPLC analysis.We study the bulk polymerization of MMA inducted by UV, and findthat in the UV of3mW/cm2, the conversion rate is growing rapidly,polymer molecular weight increases linearly with conversion andmolecular weight distribution decreases, which showes "live" feature ofcontrolled radical polymerization. The growth of molecular weight anddown of distribution index reflects the system existing the circulation ofactivation of the activited center and passivation, which makes themolecular chain length tend to be uniform.Meantime, we study the effect of light intesity on the bulkpolymerization, confirm that improving the light intensity can increasethe reaction rate, and the molcular of polymer will decrease with highdistribution index. We also study the behavior of the polymerization indifferent solvents. In the condition of solvent toluene and3mW/cm2oflight intensity, the molculer weight increases with conversion, withdecrease of distribution index, the molecular weight can reach51000. Butdistribution index was significantly higher than the bulk polymerization's,from2.8gradually reduced to1.9. In the solvent of THF, we observegood 'live' characteristics, conversion rate is growing rapidly, molecularweight linearly grow with the conversion, and the molecular weight isclose to the theory value, and finally the molecular weight of polymer is45000, the single distribution index is1.4, which shows very good'living' characteristics.Then we study the effect of monomer concentration on the reaction,and find that with high monomer concentration, the role of the solventabate, the molecular weight is high, and distribution index is bigger; with low monomer concentration, it can't effective react, so choosingappropriate monomer concentration to control the reaction process hasimportant function.We also study the influence of ultraviolet intensity and initiatorconcentration on the system. With low light intensity, the reaction rate islow; with hight intensity, active center is easy to deactive, which isagainst the control on the reaction.DMF as solvent, the molecular weight is small. The molecularweight increases with conversion, and distribution index increases andthen decreases. This shows the solvent has a very important role in thepolymerization.We also carry the polymerization of other monomers initiated byBIXAN. In the polymerization of St or GMA, the molecular increaseswith conversion, with decrease of distribution index. The conversion ofpolymerizaion of St is low, maybe due to the monomer growth rate of Stor influenced in the ultraviolet light. In the polymerization of GMA, thereaction rate is fast, the final molecular weight of polymer is8500, with1.7of distribution index. In the polymerization of BA and MA by light,we get distribution index of around1.4polymer, and this reflected theapplicability is extensive.The application of live radical polymerization of important is tosynthesize the copolymer molecular. First we study the effect of differentinitiator concentration, different monomer concentration and differentsolvents on synthetic macromolecular initiator. In the solvent of THF,1%BIXAN concentration,30%MMA monomer concentration,3Mw/cm2oflight intensity, the molecular weight of polymer is10596, and thedistribution index is1.39. We carry the chain reaction of MMA initiated by PMMA-BIXAN and the block polymerization of BA. The molecularweight increases with conversion, with decrease of distribution index, andlow to1.3. During the polymerizaion process, GPC chart shows thesingle-peak, explaining that all of the polymer chains all involve in theextender chain and embedded period of reaction, the pinacol remainstable, and no side effects occur.Through the light reaction of BIXAN and macromolecular initiatorwith TEMPO, we confirm the produce of free radicals, andmacromolecular initiator activation mechanism is belong tofracture-coupling mechanism. Put forward that the conditon of light,BIXAN generates free radicals, leading to the first generation of growthfree radicals and trigger to cause the polymerization process. We studythe formation of the activation of dormant and passivation process.Thetransformation process of the activity center and dormancy can explainthe phenomenon of the molecular weight increase and distribution indexdecrease. Through the method of TEMPO blocking we successfullycalculate the rate constant of activation rate. And then we summarize theexperimental data and experimental phenomenon, and put forward theactivity radical polymerization model of trigged by BIXAN, and themechanism of pinacol keep 'stable' in the effective radius.Free emulsion polymerization caused by BIXAN is to use a aqueousmacromolecular initiator. In the polymerization, macromolecular initiatorplays role in the initiator which generates radical to initiate thepolymerization and the role of emulsifier. During the free emulsionpolymerization, we observes 'live' feature. With the increase ofconversion, the molecular weight also grows, and the distribution indexdeclines In the study of nucleation mechanism, we observe that PAAmacromolecular initiate the polymerization of monomer, forme the original emulsion granule, with the reaction, aqueous macromolecularinitiator initiate oiliness monomer and generates the amphiphilicpolymers, when the collision of polymer constantly, independent outfitreaction happenes formed a globular latex particles.By studying the radical polymerization with BIXAN, we propose anew living radical polymerization method, with mild conditions, highactivity and relatively stable. This new Cycloketyl radical polymerizationinitiated by BIXAN can control polymerization well, free from metal,presenting important potential for practical large-scale production ofindustrial. |
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