The Atom Transfer Radical Polymerization And Degenerative Transfer Polymerization Initiated By Initiator Formed In Situ

A variety of initiators, typically alkyl halides, have been used successfully in ATRP. By far, bromine and chlorine are the most frequently used halogens. The use of alkyl iodides requires special precautions. They are light sensitive, can form metal iodide complexes with an unusual reactivity. R- alkyl halides use as initiators must have the strong electron-withdrawing and conjugation group. A novel initiator IIBN was synthesized with a cyano group on theα-position which was a small, strong electron-withdrawing and conjugation group. The low reduction potential of C-I bound made IIBN produce free radical easily and quickly combined with halogen to form stable isobutyronitrile radical. We use IIBN as an initiator in atom transfer radical polymerization (ATRP) of MMA, and the experiment result indicated that IIBN was simultaneity worked as a transfer agent in the polymerization system.1. A novel initiatorα-iodoisobutyrontrile (IIBN) was synthesized from the reaction of I2 with 2, 2′-azobisisobutyronitrile (AIBN) in methyl methacrylate (MMA). The product was analyzed by 1H-NMR spectrum. The optimal reaction conditions were studied.2. IIBN was used as an initiator for atom transfer radical polymerization (ATRP) of MMA and simultaneity as a transfer agent in the system using six catalyst/ligand systems: CuCl/PMDETA,CuCl/MA5-DETA,CuBr/PMDETA,CuBr/MA5-DETA,FeCl2·4H2O/MA5-DETA and FeCl2·4H2O/PMDETA. The influence of catalyst/ligand systems in the polymerization was studied. The influence of temperature and the molar ratio of materials in the polymerization also were investigated. Results showed the polymerization was well-controlled and the produced polymer were with low polydispersities (PDI: 1.07 -1.35). The initiator efficiency of IIBN was rather high. The polymerization using rail system was faster than that of copper system. More initiator made the polydispersities narrower but initiator efficiency lower. Scheme 1 showed the mechanism. In the system, when more R-X (IIBN) added, the balance would shift to right, produced a lot of free radicals, which lead to more possibilities of double-base termination, therefor a part of radicals could not participate in polymerization. As a result the initiator efficiency was low. On the other hand, IIBN in the system which was using as a transfer agent for Degenerative Transfer Polymerization (DT) also made portion radicals go to dormancy. In fact there are two mechanisms in the system: ATRP and DT.Results exhibit polymerizations were well-controlled and the polymers were have low polydispersities (PDI: 1.05-1.25), and the initiator efficiency of IIBN was high. The linearity of the semilogarithmic plot of Ln ([M]0/[M]) vs time for MMA indicated the polymerizations were first-order, concentration of the growing radicals remained constant throughout reaction time. The direct employment of IIBN as an initiator for ATRP and a transfer agent for DT is a simple, effective and convenient method.