Construction Of "Green" And Highly Efficient ATRP Catalytic System

The advent of atom transfer radical polymerization （ATRP） provides a simple way tosynthesize well-defined polymers with controlled molecular weights and narrow molecularweight distributions. Current research of ATRP catalyst system is mainly focused on:（1）developing highly efficient iron-mediated ATRP catalyst system based on itscharacteristics of low toxicity, abundance and biocompatibility;（2） exploring high-activecatalysts to reduce of the amount of transition metal;（3） enhancing polymerization ratewhile maintaining controllability;（4） designing “green”, recyclable and efficient ATRPcatalytic system. These new ATRP techniques for construction of “green” and highlyefficient ATRP catalytic system have been developed by employing higher oxidation statecatalyst （i.e., Cu（II） complex） and reduceing the amount of catalyst. In view of “green” andhighly efficient ATRP, the main contents and conclusions are summarized as follows:（1） In order to overcome some drawbacks of normal ATRP and reverse ATRP, animproved ATRP technique, copper-mediated activators generated by electron transfer forATRP （AGET ATRP） process, has been developed by Matyjaszewski’s group in2005.Iron has attracted extensive attentions owing to its low toxicity, being readily abundant,and biocompatibility though its complexes are generally considered to be inferior to copperor ruthenium complexes for the control of polymerization. Based on the advantage ofAGET ATRP and iron salts, a series of “green”, efficient iron-mediated AGET ATRP weredeveloped. In chapter Ⅳ, commercially available ligand （tris（3,6-dioxaheptyl）amine,TDA-1） was successfully used for iron（III）-mediated activator generated by electrontransfer atom transfer radical polymerization （AGET ATRP） of St in bulk or solution.Polymerization can also be directly performed in the presence of limited amount of air,which makes operation quite easy. A series of phosphorus-containing ligands wereemployed to establish a novel polymerization system for the iron（III）-mediatedpolymerization of methyl methacrylate （MMA） solely using FeCl₃·6H₂O or FeBr3as thecatalyst without any additional initiators or reducing agents. And the mechanism withoutadditional initiators was discussed in detail. A series of commercially available imidazole salt were used as a novel ligand for activator generated by electron transfer atom transferradical polymerization （AGET ATRP） of MMA in bulk or solution mediated by ppm levelof iron（III） catalyst. Then, values of cyclic voltammetry （CV） for the FeCl₃.6H₂Ocomplexes in the presence of different ligand were measured using acetonitrile as thesolvent to choice highly select efficient catalytic systems, which provides a guildline forselection of proper iron catalysts in application.（2） Compared with conventional radical polymerization, ATRP shows much slowerpolymerization rate, which is not favourable in commercial process. It becomes animportant goal for chemists to enhance the polymerization rate while keeping goodcontrollability for polymerization. In chapter Ⅴ, we reported that a series of catalyticamounts of base （inorganic bases （i.e., NaOH, Na₃PO₄, NaHCO₃and Na₂CO₃） and organicbases such as pyridine and triethylamine or neutral and basic Al2O₃） can enhance thepolymerization rate of the iron-mediated AGET ATRP of styrene with controlledmolecular weights and molecular weight distributions. It is noted that all thepolymerizations of novel rate-enhancement methods can also be carried out in the presenceof limited amounts of air. The nature of “living”/controlled free radical polymerization inthe presence of base was confirmed by chain extension experiments. Cyclic voltammetry（CV） measuments proves that base play an important role in ATRP catalytic systems.（3） Thermoregulated phase-transfer catalysis （TRPTC） system based on a cloud pointof nonionic ligands is becoming especially spectacular due to its facile separation just bychanging the temperature of the reaction system, and it has been successfully applied invarious types of organic reactions. Importantly, ATRP reaction system and the oil solublemonomers are similar in the aspects of the transition metal salt, ligand and substrates inorganic reaction, respectively. TRPTC system can be successfully applied in ATRP basedon the samilarlity with a cloud point of nonionic ligands in organic reaction system. Inchapter Ⅵ, a novel strategy via thermoregulated phase-transfer catalysis （TRPTC） toseparate catalyst in aqueous/organic biphasic system has been successfully established in acopper-mediated atom transfer radical polymerization （ATRP） of methyl methacrylate（MMA）, using a thermo-responsive PEG-supported dipyridyl ligand （PSDL） as the ligandand RAFT agent as the initiator. The catalyst complex can transfer into the organic phasefrom initial aqueous catalyst solution at the reaction temperature （90oC） to catalyze thehomogeneous polymerization of MMA, then it retransfer into the aqueous solution from the organic phase to separate the catalyst from the polymerization solution once cooled toroom temperature （25oC） while keeping well-controlled product （PMMA） in organic layer.In addition, TRPTC ATRP can be conducted in the presence of a limited amount of air,without sacrificing the controllability over polymerization; in addition the catalyst can berecycled simply yet effectively by changing of the temperature.