44542-G7
Development of Transition Metal Catalysts for Radical (Co)Polymerization of Nonpolar Olefins and Polar Monomers
Copolymers of olefins and polar monomers are industrially very attractive materials and have a wide variety of applications in materials that require extreme toughness or superior sealing properties. Conventionally, olefins are copolymerized with polar monomers in the presence of free radical initiators. However, the synthesis often requires extreme reaction conditions such as elevated temperatures and pressures and yields copolymers which are enriched in polar monomer due to the large differences in reactivity ratios. The main objective of our project is to rationally develop catalytic systems that can be used in radical copolymerization of olefins and polar monomers based on changing the reactivity ratios through complexation of the monomers with copper(I) complexes. This change can be induced by altering the electronic properties of the coordinated double bond by varying the relative contributions of ¹-backbonding from the metal center and σ-donation from the double bond.
The systematic approach to this project involves (a) fundamental investigation of the parameters that affect copper(I)-p-olefin(polar monomer) bond strength, (b) synthesis and activity studies of model compounds in free radical cyclization reactions and (c) homo- and copolymerization of nonpolar olefins and polar monomers in the presence of copper(I) complexes.
During the past year, our research group has concentrated on the synthesis and characterization of copper(I) complexes with bidentate nitrogen based ligands containing polar and nonpolar monomers. As a result, we were able to synthesize and characterize novel copper(I)/2,2'-bipyridine complexes [CuI(bpy)(¹-CH2CHCOOCH3)][A] (A = CF3SO3-, ClO4- and PF6-). In all three complexes, weak coordination of the counterion was observed. In our attempt to synthesize well-defined copper(I) complexes of polar and nonpolar monomers without counterion coordination, we came across very unusual class of compounds. In the presence of bidentate nitrogen based ligands (NN) and weakly coordinated counterion BPh4-, copper(I) complexes readily form neutral CuI(NN)(BPh4). Such complexes with 2,2'-bipyridine, 1,10-phenanthroline and 3,4,7,8-tetramethyl-1,10-phenantrholine have been isolated and characterized. In all three complexes the counterion was coordinated to the copper(I) center through two p bonds of phenyl rings. This was the first time that such coordination was observed in transition metal complexes. The synthesized CuI(NN)(BPh4) complexes are excellent candidates for radical copolymerization of polar and nonpolar monomers. In the presence of alkenes, they readily loose coordinated counterion to form well-defined [CuI(NN)(p-alkene)][BPh4] complexes. Coordinatively unsaturated [CuI(NN)(p-alkene)][BPh4] complexes can further coordinate radicals and include coordination polymerization. Detailed mechanistic and kinetic studies of these systems are currently conducted in our laboratories.
