| The structure of the nitroxide compounds has a crucial impact on the regulation behavior in nitroxide mediated radical polymerization(NMP).Alkyl fragment and nitroxide containing in dormant species alkoxyamine of nitroxide mediated radical polymerization decide the dissociation rate of NO-C bond and thus determine the nature of photo-living radical polymerization.Consider alkyl fragment structure are based on monomers'structure,researches on NMP rarely concern on it because monomer type does not decide photo-living polymerization nature.Right now for the nitroxide mediated radical polymerization research focus attention on design and synthesis functionalized nitroxide and explores its property as effective regulate agent.The appearance of photo-induced polymerization solves the two drawback of nitroxide mediated polymerization:limited number of monomer families and the need for high reaction temperatures.The photopolymerization not only conforms to the green chemistry development,but also allows perform NMP to methacrylates.In order to further improve the efficiency of nitroxide mediated photo-polymerization(NMP2),it is important to expand the scope of photosensitive nitroxides and energy transfer machanism.According to the foregoing,we have designed and synthesized several different types of nitroxide compounds:nitroxides with coordination structure,nitroxides containing organic chromophore(denote as Bi-TEMPO and Pe-TEMPO individually).Selected photosensitive nitroxide was chosen to explore its properties in the photo-living radical polymerization behavior under different source of light such as sunlight and high pressure mercury lamp.The main works and conclusions of this paper are as follows:1.4-amino-2,2,6,6-tetramethylpiperidine and its nitroxide derivative as reacted with salicylaldehyde and p-nitrosalicylaldehyde spectively to retained 4 types of Schiff base ligands:4-(salicylaldehyde Schiff base)-2,2,6,6-tetramethyl-piperidine(SLi);4-(p-nitro-salicylaldehyde Schiff base)-2,2,6,6-tetramethyl-piperidine(SL2);4-(salicylaldehyde Schiff base)2,2,6,6-tetramethylpiperidine-l-oxyl(SL3);4-(p-nitro-salicylaldehyde Schiff base)2,2,6,6-tetramethylpiperidine-1-oxyl(SL4).By coordinating through Schiff base structure,several complexes retaining hindered amine structures were form.The structure of the complex were characterized by single crystal-XRD,other instrumental analysis such as TGA,XRD,ESR,UV-Vis and FS were employed to characterize the property of the complexes.The single crystal structure of the complexes was first reported.2.4-pyrene-4-hydroxy-2,2,6,6-tetramethylpiperidine-l-oxyl(Bi-TEMPO)was prepared by three-steps organic synthesis using triacetonamine and pyrene as starting material.4-perylene-4-hydroxy-2,2,6,6-tetramethylpiperidine-l-oxyl(Pe-TEMPO)was obtained in the same manner.The chemical structure of intermediates in each synthetic step was confirmed by FTIR,1H NMR,EA and MS.Two target products' exact structure was characterized by single crystal XRD.The spectral characteristics of prepared compounds were determined by UV-Vis,ESR and FS.The crystal structure of photosensitive nitroxides was first reported in this paper.3.Photo-sensitive nitroxide Pe-TEMPO and Bi-TEMPO were chosen to explore its properties as control agent innitroxide mediated photopolymerization under sunlight.The use of lower energy wavelength is an important step in the application of such photo-induced living polymerization technology in medical application and material science.First,we presented for the first time temporally controlled by turning on/off the light in nitroxide mediated photopolymerization confirmed by time resolved infrared spectroscopy.Photopolymerization rheological test under UV radiation confirmed that there was an induction period in the beginning of the control/living polymerization.The viscosity of the system did not change with time during the induction period.The viscosity of the system increased gradually,and the change trend was obvious.The optimal photoinitiator for Bi-TEMPO/Pe-TEMPO mediated photopolymerization under sunlight was Irgacure819.In Bi-TEMPO mediated photopolymerization,when the initiator content is 1.8 wt.%to monomer,the ratio of mole mass of photoinitiator and mediator is 1.0:1.3,polymer molecular weight match with theoretical molecular weight.Under this condition,Bi-TEMPO mediated photopolymerization of MMA in bulk mediated by Bi-TEMPO were carried out,the reaction kinetics of the polymerization was investigated.The results show that monomer conversion(ln[M]0/[M]t?t)increased linearly with time,and the number-average molecular weight increased almost linearly with monomer conversion,it is a kinetic character of controlled/living radical polymerization,the polydispersity index(PDI)and the molecular weight distribution of the PMMA homopolymers were narrow as we expectation,PDI=1.50?1.90.In Pe-TEMPO mediated photopolymerization,when the initiator content is 1.2 wt.%to monomer,the ratio of mole mass of photoinitiator and mediator is 1.0:1.1,polymer molecular weight match with theoretical molecular weight.Under this condition,Pe-TEMPO mediated photopolymerization of MMA in DMF solution was carried out,the reaction kinetics of the polymerization was investigated.The results show that monomer conversion(ln[M]0/[M]t?t)increased linearly with time,and the number-average molecular weight increased almost linearly with monomer conversion,it is a kinetic character of controlled/living radical polymerization,the polydispersity index(PDI)and the molecular weight distribution of the PMMA homopolymers were narrow as we expectation,PDI=1.40?1.80.Chain extensions with styrene were carried out using PMMA macromolecule alkoxyamine as an initiator/mediator to investigate livingness of the synthesized homopolymers.The GPC results show that the polymerization system is living polymerization and can be used for photosynthesis of various block copolymers..4.Based on the Bi-TEMPO/Pe-TEMPO mediated radical polymerization results,photo-induced in situ polymerization technique was proposed using the two novel nitroxide to induced alkyl bromide generate alkyl radical in polymerization mediated under UV radiation for living radical polymerization.The generation of carbon-centered radicals fromalkyl bromides and formation of corresponding alkoxyamine in DMF solution is confirmed by NMR and ESR.Result of Rheology test under UV irradiation was consistent with the above mentioned with photopolymerization initiated by photoinitiator Igacure819,which supports the feasibility of photo-induced in situ polymerization.The halogenated compounds sources,the monomer feed ratio,solution effect,and the ratio of alkyl bromide/control agents on the reaction kinetics of photopolymerization were investigated.Among the halogenated compounds sources,using methyl alpha-bromophenylacetate as functional initiator can achieve better polymerization rate and conversion.DMF was best solution for photo-induced in situ NMP polymerization.At initiator/mediator/monomer = 4/1/200,polymer molecular weight match with theoretical molecular weight.Under this condition,the reaction kinetics of the polymerization was investigated.The results show that monomer conversion(ln[M]0/[M]t?t)increased linearly with time,and the number-average molecular weight increased almost linearly with monomer conversion,it is a kinetic character of controlled/living radical polymerization,the polydispersity index(PDI)and the molecular weight distribution of the PMMA homopolymers were narrow as we expectation,PDI=1.50?1.90.Chain extensions with styrene were carried out in the same manner in previous study.Both under thermal and light irradiation,Using PMMA macromolecule alkoxyamines as initiator/mediator were capable to obtain PSt-b-PMMA copolymers with narrow polydispersity.The investigation livingness character was confirmed by GPC result.In conclusion,photo-induced in situ polymerization mediated by Bi-TEMPO/Pe-TEMPO is a living radical polymerization system and can be used for photosynthesis of various block copolymers. |
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