Construction Of Visible Light Induced Iodine-Mediated RDRP In Water And Role Of Iodine-Mediated RDRP In Dispersity Control

As we all know,reversible-deactivation radical polymerization(RDRP)methods have gradually become a powerful tool for polymer design and synthesis of polymers with precision architectures,programmable compositions and controlled molecular weights and molecular weight distributions.As a simple,mild polymerization strategy,iodine-mediated RDRP has a wide range of applicable monomers and strong prospects of industrial application;there are already some commercial products in use in the fields of surfactants,medical equipment,and electronics,although some disadvantages remain to be resolved such as uncommercial catalysts and high cost.Photochemistry which began in the early 20th century is an effective method for chemical synthesis at ambient temperature.Recently,the combination of photochemistry and polymerization systems greatly facilitate the synthesis and modification of polymers with complex structures benefitting from the attractive features of photochemistry such as space-time controllability and wavelength selectivity of external light sources.The advancement of photo-induced RDRP methods also benefits from the rapid development of light-emitting diode(LED)technology which is low-cost,high-precision and simple.Polymer dispersity(D)which represents the width of molecular weight distributions(MWDs)of materials is a significant parameter in polymer synthesis since the width and shape of MWDs will greatly affect the properties of materials.Polymeric materials with narrow or wide MWDs often exhibit complementary properties.Hence,polymer dispersity control has gradually become the focus of attention in polymer synthesis and it is of great significance and potential application prospects in tailoring polymer dispersity.This thesis focuses on the construction of a green and highly efficient visible light induced iodine-mediated RDRP strategy and the application of visible light induced iodine-mediated RDRP in polymer dispersity control.The main contents and conclusions are as follows:System I:Construction of Visible Light Induced Iodine-Mediated RDRP of Methacrylates in Water.In this work,the green solvent-"water" has been proved as an efficient catalyst in the visible light induced iodine-mediated RDRP system.Therefore,a facile and environmentally friendly iodine-mediated RDRP methodology with only three components has been proposed successfully under the irradiation of blue LED at ambient temperature.Herein,2-iodo-2-methylpropionitrile(CP-I)was used as the alkyl iodine initiator and H2O played the dual role of catalyst and solvent.Both water-soluble monomers(poly(ethylene glycol)methyl ether methacrylate(PEGMA),2-hydroxyethyl methacrylate(HEMA),and 2-hydroxypropyl methacrylate(HPMA)etc.)and oil-soluble monomers(methyl methacrylate(MMA)and benzyl methacrylate(BnMA))were applicable to this strategy.Well-defined polymers(PPEGMA,PHEMA and PHPMA)with narrow molecular weight distributions(Mw/Mn<1.2)and amphiphilic block copolymers which can form nanospheres in situ in water(PPEGMA-b-PBnMA and PPEGMA-b-PHPMA)were successfully prepared.The bulk polymerization of MMA in the presence of trace amounts of water was conducted to investigate the role of water in this system.Generally,water acts as both a solvent and a catalyst in the system and it has an additionally positive effect in accelerating the polymerization.Obviously,this simple strategy provides an efficient path to well-defined homopolymers of methacrylates and the clean synthesis of amphiphilic copolymer nanoparticles in situ under the irradiation of visible light at ambient temperature.System ?:Application of Iodine-mediated RDRP in Polymer Dispersity Control.In previous work,we found that acrylates can not be polymerized in the visible light induced iodine-mediated RDRP system mentioned above while they can act as the capping agent in visible light induced iodine-mediated RDRP of methacrylates which provides an excellent strategy for us in polymer dispersity control by using iodine-mediated RDRP.Apart from this,dormant species with acrylate-terminal which has been capped with iodine can be used as the macroinitiator in single-electron transfer-degenerative chain transfer living radical polymerization(SET-DTLRP).Therefore,the focus here is to explore the method of tailoring molecular weight distributions while retaining the polymer fidelity with these two iodine-mediated RDRP strategies.In order to enhance the solubility of each component in this system and expand the range of applicable monomers,we utilized the relatively economical organic reagent 1,3-dimethyl-2-imidazolinone(DMI)as the solvent.MMA and n-butylacrylate(n-BA)were chosen as the model monomers for methacrylates and acrylates respectively for investigation.For reversible complexation mediated living radical polymerization(RCMP)of MMA in the presence of different amounts of n-BA under blue LED irradiation.when the feed molar ratios of[MMA]0/[n-BA]0=98/2,95/5,90/10,80/20,75/25,D of polymers were in the range of 1.31 to 1.62;without n-BA,D of PMMAs were mostly around 1.2.Choosing ethyl 2-iodo-2-phenylacetate(EIPA)as the initiator,we prepared the macroinitiator at the molar ratio[MMA]0/[n-BA]0/[EIPA]0= 90/10/1 and then obtained the block copolymer PMMA-b-P(n-BA)successfully with SET-DTLRP.Thereby,combined with these two iodine-mediated RDRP methods(blue LED light-induced RCMP and SET-DTLRP),we can achieve polymer dispersity control at room temperature while maintaining the "living" feature of polymers.