Study On Reaction Kinetics Of Photo-living Radical Polymerization Of MMA Mediated By Photosensitized Nitroxide Of Hindered Amine

Due to many advantages, such as higher rate of polymerization, lower reaction temperature and to be suitable for extensive monomers, nitroxide mediated photopolymerization (NMPP) have been applied to controlled/living radical polymerization in recent years, providing a new tehcnique to solve the existing problems in heat-initiated NMP and it has become a focus of scientific research. In this paper, a novel photosensitive hindered amine nitroxide (Q-TEMPO) were synthesized firstly. And then, the reaction kinetics of MMA photopolymerization in bulk such as the kind of initiator and content, the light intensity and different monmers have been investigated in detail. The controlled mechanism of Q-TEMPO as a mediator was discussed. Finally, using PMMA-Q-TEMPO as macromolecular initiator, PMMA-b-PIBOMA diblock copolymers were synthesized by NMPP in the same conditions, the main research works and conclusions are as follows:1. Using4-dimethylaminopyridine (DMAP) as a catalyst and N,N’-Dicyclo-hexylcarbodie (DCC) as dehydrolyzing agent, photosensitive hindered amine nitroxide (Q-TEMPO) was synthesized by the esterification of H-TEMPO and quinolin-2-carboxylic acid in methylene dichloride (CH2Cl2). The composition and structure of the product was characterized by element analysis, FTIR,1H-NMR, MS and EPR. The photosensitized performance of Q-TEMPO was characterized by UV-Vis spectroscopy and FS。2. The designed reaction condition of the polymerization, such as the kind of initiator and content, the light intensity and reaction time etc., were optimized by the experimental selection.3. In designed reaction condition, NMPP of MMA in bulk mediated by Q-TEMPO has been carried out, using Irgacure651as an initiator. The reaction kinetics of the polymerization were investigated. The results show that monomer conversion (ln[M]/[M0]) increased linearly with time and the number-average molecular weight (Mn) increased almost linearly with mnomer conversion, it is a kinetic character of controlled/living radical polymerization, but the polydispersity index (PDI) and the molecular weight distribution of the homopolymers are not so excellent, PDI=1.40-1.80. Then the homopolymer was characterized by GPC, FTIR and1H-NMR.4. In order to approach the reaction kinetics of MMA photopolymerization in bulk mediated by Q-TEMPO, the concentration of Q-TEMPO during the proceeding of the photopolymerization was monitored by time-resolution ESR. Some of kinetic constants quantitatively estimated as below. Decomposition rate constant (ki) of Irgacure651is1.29×10-3s-1, which is10-1000times higher than one of the thermal initiator. It is illustrated why the rate of photopolymerization is faster than the thermal one. And the equilibrium constant KE in ending-openning reaction of Q-TEMPO is5.86×1010mL·mol-1, which is1000times smaller than that of styrene thermal polymerization, which is the reason why photopolymerization is to be suitable for a wider range of monomers than the thermal one. When the photopolymerization is to be at the steady state, the concentration of the chain propagation radical [Pn·] reaches4.23×10-6mol/L, which is a higher level of the concentration of [Pn·] for controlled/living radical polymerization. It is negative to inhibition of chain termination reaction, which is also to be the main reason for PDI widenning with molecular weight increasing in the late period of photopolymerization in our experiment.5. Using PMMA-Q-TEMPO as macromolecular initiator, PMMA-b-PIBOMA diblock copolymers were synthesized by NMPP in the conditions above. The PMMA-b-PIBOMA copolymers were characterized by GPC,1H-NMR, FTIR and TGA.