Abstract
Two dinuclear cobalt complexes based on bis-diketonate ligands (ligand 1: 3,3′-(1,3-phenylene)bis(1-phenylpropane-1,3-dione); ligand 2: 3,3′-(1,4-phenylene)bis(1-phenylpropane-1,3-dione)) were successfully synthesized. The two neutral catalysts all showed satisfactory activities in the cobalt-mediated radical polymerization (CMRP) of methyl methacrylate (MMA) with the common initiator of azodiisobutyronitrile (AIBN). The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities. Mono- or dicomponent low polydispersity polymers could be obtained by using the two dinuclear catalysts under proper reaction conditions. All these improvements facilitate the implementation of the acrylate CMRP and open the door to the scale-up of the syntheses and applications of the multicomponent low polydispersity polymers.
Highlights
In recent years the development of the controlled/living techniques of radical polymerization (CRPs) was developed as an answer to the steadily increasing demand for new materials with controlled properties [1,2,3,4]
nitroxide-mediated polymerization (NMP) and atom transfer radical polymerization (ATRP) rely on the same concept, which consists of decreasing the radical concentration in the medium and the probability of irreversible termination
The catalyst activity and efficiency of cobalt catalyst are still not so high for CRPs (CMRP or ATRP). These facts mean that these catalysts coprecipitate with the polymer products after polymerization, coloring and contaminating the products
Summary
In recent years the development of the controlled/living techniques of radical polymerization (CRPs) was developed as an answer to the steadily increasing demand for new materials with controlled properties [1,2,3,4] This concept is a valuable strategy to provide a large range of polymers with well-defined molecular characteristics (length, composition and architecture), under non-very demanding conditions. The past few years have witnessed the rapid growth in the development and understanding of new CRP methods All of these methods are based on establishing a rapid dynamic equilibration between a minute amount of growing free radicals and a large majority of the dormant species. NMP and ATRP rely on the same concept, which consists of decreasing the radical concentration in the medium and the probability of irreversible termination This is achieved by reversible conversion of the growing macroradicals P? The lability of the cobalt–carbon bond under thermal and photolytic treatment, and the reversibility of its cleavage, makes cobalt complexes suitable candidates for PRE and regulation of CRP
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