Thomas Rünzi

Insertion Polymerization of Acrylate

Multiple insertions of acrylate in copolymerization with ethylene, and an insertion homo-oligomerization of methyl acrylate were observed for the first time. Key to these findings, and to mechanistic insights reported, are labile-substituted complexes as catalyst precursors.

Direct synthesis of ethylene-acrylic acid copolymers by insertion polymerization.

Neutral palladium(II) phosphinesulfonato polymerization catalysts were found to be stable toward carboxylic acid moieties and to enable direct linear copolymerization of ethylene with acrylic acid.

Reactivity of Methacrylates in Insertion Polymerization

Polymerization of ethylene by complexes [{(P^O)PdMe(L)}] (P^O = κ(2)-(P,O)-2-(2-MeOC(6)H(4))(2)PC(6)H(4)SO(3))) affords homopolyethylene free of any methyl methacrylate (MMA)-derived units, even in the presence of substantial concentrations of MMA. In stoichiometric studies, reactive {(P^O)Pd(Me)L} fragments generated by halide abstraction from [({(P^O)Pd(Me)Cl}μ-Na)(2)] insert MMA in a 1,2- as well as 2,1-mode. The 1,2-insertion product forms a stable five-membered chelate by coordination of the carbonyl group. Thermodynamic parameters for MMA insertion are ΔH(++) = 69.0(3.1) kJ mol(-1) and ΔS(++) = -103(10) J mol(-1) K(-1) (total average for 1,2- and 2,1-insertion), in comparison to ΔH(++) = 48.5(3.0) kJ mol(-1) and ΔS(++) = -138(7) J mol(-1) K(-1) for methyl acrylate (MA) insertion. These data agree with an observed at least 10(2)-fold preference for MA incorporation vs MMA incorporation (not detected) under polymerization conditions. Copolymerization of ethylene with a bifunctional acrylate-methacrylate monomer yields linear polyethylenes with intact methacrylate substituents. Post-polymerization modification of the latter was exemplified by free-radical thiol addition and by cross-metathesis.

Control of molecular weight in Ni(II)-catalyzed polymerization via the reaction medium

The reaction medium controls polymerization with highly active (kappa(2)-P,O)-phosphinesulfonato nickel methyl complexes to afford polyethylenes ranging from low molecular weight (M(n)) branched material to high molecular weight (M(n)) strictly linear polymer.