Person: Rünzi, Thomas
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Reactivity of Functionalized Vinyl Monomers in Insertion Copolymerization
We report the reactivities of a comprehensive range of polar vinyl comonomers and 1-olefins in the copolymerization with ethylene by [{(o-MeOC6H4)2PC6H4SO3}PdMe(L)] from pressure reactor studies (95 °C, 3–20 bar), as defined by rE = kethylene/kcomonomer from Markov statistics. 13C NMR chemical shifts of the monomers’ β vinyl carbon atom and Charton and Sterimol parameters were found to be appropriate descriptors for the monomers’ electronic nature and steric demand, respectively. A comprehensive picture of their impact on monomer reactivity and also regioselectivity of insertion arises. This shall also allow for predictions of the reactivity of other monomers.
Generation of novel polymeric materials and catalyst deactivation pathways in polar vinyl monomer insertion copolymerization
In the past six years, the longstanding issue of polar vinyl monomer insertion polymerization has seen strong advances. A broad range of monomers, including even vinyl acetate and acrylonitrile, is now amenable to copolymerization with ethylene. Also, a mechanistic understanding has been established which identifies relevant limitations. Thus, coordination of the functional group of free or incorporated polar monomer to the active sites reversibly hinders chain growth and slows down polymerization.
This background raised the following
issues, which are addressed in this thesis. While a range of different copolymers has been characterized on a molecular level, studies of relevant material properties had been lacking. This is a prerequisite for identifying potential applications.
The scope of polar vinyl monomers amenable to insertion polymerization excludes acidic polar groups, although incorporation of such groups is very desirable for e.g. compatibility with inorganic surfaces.
Mechanistically, reversible deactivation pathways are quite well understood. However, the possibility of irreversible deactivation routes had not been considered at all for these copolymerizations, although this would obviously have a decisive impact.
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.
Control of molecular weight in Ni(II)-catalyzed polymerization via the reaction medium
The reaction medium controls polymerization with highly active (κ2-P,O)-phosphinesulfonato nickel methyl complexes to afford polyethylenes ranging from low molecular weight (Mn) branched material to high molecular weight (Mn) strictly linear polymer.
Nanocomposites of Phosphonic-Acid-Functionalized Polyethylenes with Inorganic Quantum Dots
Insertion of diethyl vinyl phosphonates and free vinyl phosphonic acid, respectively, into [(P^O)Pd(Me)(dmso)] ((P^O) =κ2-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) (1-dmso) occurs in a 2,1- as well as 1,2-fashion, to form a four-and a five-membered chelate [(P^O)Pd{κ2-C,O-CH(P(O)(OR)2)CH2CH3}] and [(P^O)Pd{κ2-C,O-CH2CH(P(O)(OR)2)CH3}] (R = H, Et). No decomposition or other reactions of 1 by free phosphonic acid moieties occur. Copolymerization in a pressure reactor by 1-dmso yields linear random poly(ethylene-co-diethyl vinyl phosphonate) and poly(ethylene-co-vinyl phosphonic acid). In these copolymerizations, reversible coordination of the phosphonate moieties of free monomer as well as chelate formation by incorporated monomer retards chain growth as also evidenced by relative binding studies of diethyl phosphonate towards 1. Post-polymerization emulsification of poly(ethylene-co-vinyl phosphonic acid) together with CdSe/CdS quantum dots (QDs) yields submicron (ca. 50 nm from dynamic light scattering (DLS) and transmission electron microscopy (TEM)) polymer particles with the QDs embedded in the functionalized polyethylene in a nonaggregated fashion. This embedding benefits the fluorescence behavior in terms of continuous emission and life-time as revealed by wide-field fluorescence measurements. These composite particle dispersions are employed as a ″masterbatch” together with an aqueous high density polyethylene (HDPE) dispersion to generate thin films (by spin-coating) and bulk materials (from the melt), respectively, in which the inorganic nanoparticles remain highly disperse.
Activation and Deactivation of Neutral Palladium(II) Phosphinesulfonato Polymerization Catalysts
Saturated polar-substituted polyethylene elastomers from insertion polymerization
Saturated, polar-substituted elastomers consisting of a linear polyethylene backbone are prepared directly by insertion copolymerization of ethylene with polar-functionalized vinyl monomers employing functional-group tolerant catalysis. This unprecedented approach to elastomers is compatible with a wide range of different crosslinking chemistries. Crosslinking of the materials occurs efficiently, as concluded from gel contents and spectroscopic observations. Mechanical and thermal properties are revealed by dynamic mechanical analysis.
Reactivity of Methacrylates in Insertion Polymerization
Polymerization of ethylene by complexes [{(P^O)PdMe(L)}] (P^O ) κ2-(P,O)-2-(2-MeOC6H4)2-PC6H4SO3)) 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 ΔHq ) 69.0(3.1) kJ mol-1 and ΔSq ) -103(10) J mol-1 K-1 (total average for 1,2- and 2,1-insertion), in comparison to ΔHq ) 48.5(3.0) kJ mol-1 and ΔSq)-138(7) J mol-1 K-1 for methyl acrylate (MA) insertion. These data agree with an observed at least 102-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.
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.