Construction Of ATRP Systems With Low Metal Catalyst Residue In Polymers

The invention of atom transfer radical polymerization(ATRP) provides great convenience for designing end-functional polymers, different chain structure polymers(block, gradient, and random) and topological polymers(cyclic polymer and brush polymer, etc.), with controlled molecular weights and narrow molecular distributions. Now, the research highlighted in ATRP are as follows:(1) expanding monomer types of ATRP,(2) developing “green” iron-mediated ATRP systems;(3) exploring ATRP system with mild polymerization conditions, such as photo-induced ATRP at room temperature;(4) Reducing the concentration of metal catalyst used in ATRP by improving the activity of catalyst;(5) Highly efficient separation and recycling of metal catalyst, and(6) exploring metal-free ATRP system. In this dissertation, a series of works focusing on reducing metal catalyst residues in polymers to build “green” ATRP systems and therefore widen the scope of the application of ATRP. The main research contents and conclusions of this paper are as follows:(1) Highly Active ppm Level Organic Copper Catalyzed Photo-Induced ICAR ATRP at Room Temperature. The metal catalyst used in ATRP can be reduced to ppm level by initiators for continuous activator regeneration process. Meanwhile, photo-induced ATRP at room temperature is a mild and efficient process. By combination both of advantages, we developed a highly active ppm level organic copper catalyzed photo-induced ICAR ATRP system with methyl methacrylate(MMA) as the model monomer. In chapter II of this dissertation, we established a novel photo-induced homogeneous ATRP system at 30 oC using organic copper salt(Cu(SC(S)N(C2H5)2)2), N,N,N′,N′′,N′′- pentamethyldiethyl enetriamine(PMDETA), 2-bromophenylacetate(EBPA) and(2,4,6-trimethylbenzoyl) diphenylphosphine oxide(TPO) as a photo-induced metal salt, typical ligand, ATRP initiator and photo-induced radical initiator, respectively. It is found that well-defined polymers can be obtained even with the amount of(Cu(SC(S)N(C2H5)2)2 decreasing to a 1.56 ppm, with the molecular weight of the PMMA increasing linearly with monomer conversion while maintaining a narrow molecular weight distributions(Mw/Mn ≤ 1.3).(2) Construction of Novel Thermoregulated Phase Transfer Catalysis(TRPTC) ATRP for Facile and Highly Efficient Catalyst Separation and Recycling in situ. The concentration of residual metal catalyst in obtained polymers can be reduced to ppm level by highly efficient separation the catalyst from target polymers. Recently, inspired by the application of TRPTC in organic reactions, our group successfully developed a new way to recovery and recycling of copper catalyst of ATRP in water/organic biphasic system named TRPTC ATRP, which provides a new way to separate metal catalyst and polymer efficiently in situ. However, from the viewpoint of catalyst recycling, the fatal drawbacks of the reported systems are the relatively low catalyst recovery efficiency(less than 70%), high copper residual and not suitable for alkyl halide. In chapter III, a complex of highly active thermoregulated ligand, monomethoxy poly(ethylene glycol)-350(MPEG350)-supported substituted dipicolylamine, L350 and CuBr2 was used as a novel highly active thermoregulated catalyst. From the polymerization kinetics of MMA using the recycled catalyst for three times, the inductin periods increased with recycling time(from ~ 0.25 to 0.5 h) and polymeration rate kept constant, that is to say, the recovered catalyst has no obvious lose in activity. Meanwhile, the catalyst residue in polymers is less than 2 ppm and the recycling efficiency of catalyst complex in water kept more than 95% even after 5 times of recovery experiments while keeping narrow molecular weight distributions(Mw/Mn ≤ 1.33). In chapter IV, the new kind of thermoregulated ligand(PPEGMA-BPMA) base on poly(poly(ethylene glycol) methylether methacrylate(PPEGMA) was synthesized successfully. The complex of PPEGMA-BPMA and CuBr2 was used as novel thermoregulated catalyst in water/p-xylene biphasic ICAR ATRP with a typical and commercially available alkyl halide, EBPA, as the ATRP initiator. The obtained well-defined PMMA with controlled molecular weight and narrow molecular distributions(Mw/Mn ≤ 1.25). And during 8 times recycling expriments, catalytic activity of the recycled catalyst decreased slightly(monomer conversion decreased from 68.2 % to 57.7 % for 18 h), copper residual in polymer was very low([Cu]org ≤ 3.6 ppm). The successful application of alkyl halide in water/organic biphasic ATRP system greatly expand the range of application of TRPTC ATRP.(3) Construction of ATRP System for Hydrohpilic Monomers with Highly Efficient Catalyst Separation and Recycling in situ. Hydrophilic polymers have been widely used in scientific research and mass market products. The concentration of metal catalyst used in ATRP for synthesizing structure controlled hydrophilic polymers is somehow high, and removing catalyst from hydrophilic polymers is a challenging task by post-treatment. So establishing a system, which focused on ATRP of hydrophilic monomers for catalyst separation and recycling in situ is very practical significance. The key for the successful separation and recycling of metal catalyst depends on the design of an oil-soluble ligand and the selection of biphasic solvent system. So in chapter V, a random copolymer of octadecyl acrylate(OA) and MA-Ln(2-(bis(pyridin-2-ylmethyl)amino)ethyl acrylate), POA-ranP(MA-Ln) was designed as the nonpolar macroligand and heptane/ethanol was selected as the biphasic solvent. It should be noted that the polymerization was conducted in a homogeneous condition. However, a biphasic system could be easily formed in situ after adding 10 vol% of water into the homogeneous phase, and therefore catalyst complex(in heptane phase) could be separated and recycled in situ. During 6 times recycling experimens, the catalytic activity increased slightly(conversions of PEGMA500 increased from 50.6 % to 62.1 % for 14 h), the residual of copper catalyst in polymer solution was low([Cu]polymer ≤ 9.5 ppm). Consideration of the mild and efficient features of visible light, in chapter VI, the ICAR ATRP of PEGMA500 was developed with the synthesized nonpolar hybrid copper complex(BCc) as the catalyst, EBPA and camphorquinone/triethylamine as alkyl ATRP initiator and binary visible light radical initiator, respectively. The monomer conversion reached nearly 100 % after irradiation for 22 h under 9.6 w while LED. And the polymerization could also be conducted smoothly under blue, green and purple LEDs. During the recycling experiments, the catalyst activity was almostly unchanged, the monomer conversion almost reached quantitative level(> 96 %), obtained polymer owned controlled molecular weights and narrow molecular weight distributions(Mw/Mn ≤ 1.28) and the concentration of residual BCc in hydrophilic polymers was low([Cu]polymer ≤ 20 ppm).