Insertion polymerization of electron-deficient vinyl monomers
Final Report Abstract
This project provided far-reaching fundamental insights into catalytic copolymerizations of ethylene with polar vinyl comonomers. For neutral Pd(II) phosphinesulfonato complexes, one of the key catalyst systems capable of performing such copolymerizations, the reversible equilibria which slow down chain growth by coordination of functional groups from the comonomer were identified and quantified. Further, irreversible deactivation pathways by reductive elimination of the growing chain to the phosphinesulfonato ligand were revealed. The correlation of the catalysts’ structure with the underlying insertion events was explored, resulting in the ability to invert the stereoregularity of acrylate insertion to the electronically disfavored 1,2-mode. Also, the stereochemistry of 2,1-insertion can be directed by the phosphine substituents, though not yet for multiple consecutive insertions in a stereoregular chain growth. An approach to place binding sites for the functional groups introduced into the growing chain in the catalyst, in order to relieve reversible deactivation was explored but remained on the level of developing preparative routes to such catalysts. The reactivity of comonomers in the title copolymerizations was quantified and systemized from their observed ethylene copolymerization parameters and regiochemistry, and correlated with the comonomers’ steric demand and 13C NMR shifts as a measure of their electronics. For neutral Ni(II) salicylaldiminato catalysts as another prototypical key catalyst system, conflicting reports with regard to their behavior towards polar comonomers could be resolved. Catalytic insertion chain growth and free-radical chain growth can occur simultaneously, without interfering with one another. Initiating radicals can be formed from catalyst precursors, for example by P-C bond cleavage in monodentate phosphines. Deliberately generated radicals from added free radical initiators can be incorporated as chain ends in polyethylene chains grown by insertion polymerization. Evidence for both incorporation as a chain-initiating as well as -terminating end group was observed. In view of this robustness of the chain growth procedure, radical-generating end groups were incorporated as chain ends in a chain transfer polymerization. These allowed for a controlled free-radical polymerization of acrylates to form polar-apolar diblock copolymers by sequential chain growth and controlled radical growth. The methodology employed for these studies were primarily NMR mechanistic studies and pressure reactor polymerization experiments, in addition to organic and organometallic synthesis of catalysts. DFT studies were performed in a cooperation.
Publications
- (2020) Catalytic Chain Transfer Polymerization to Functional Reactive End Groups for Controlled Free Radical Growth. Macromolecules 53 (7) 2362–2368
Stadler, Sonja M.; Göttker-Schnetmann, Inigo; Fuchs, Amelie S.; Fischer, Stephan R. R.; Mecking, Stefan
(See online at https://doi.org/10.1021/acs.macromol.0c00241) - Solid-Supported Single-Component Pd(II) Catalysts for Polar Monomer Insertion Copolymerization. ACS Catalysis 2014, 4, 2672 – 2679
P. Wucher, J. Schwaderer, S. Mecking
(See online at https://doi.org/10.1021/cs5005954) - Role of Radical Species in Salicylaldiminato Ni(II) Mediated Polymer Chain Growth: A Case Study for the Migratory Insertion Polymerization of Ethylene in the Presence of MMA. J. Am. Chem. Soc. 2015, 137, 14819 – 14828
F. Ölscher, I. Göttker-Schnetmann, V. Monteil, S. Mecking
(See online at https://doi.org/10.1021/jacs.5b08612) - Reactivity of Functionalized Vinyl Monomers in Insertion Copolymerization. Macromolecules 2016, 49, 1172 – 1179
N. Schuster, T. Rünzi, S. Mecking
(See online at https://doi.org/10.1021/acs.macromol.5b02749) - Incorporation of Radicals During Ni(II)-Catalyzed Ethylene Insertion Polymerization. ACS Catal. 2019, 9, 2760 – 2767
S. Stadler, I. Göttker-Schnetmann, S. Mecking
(See online at https://doi.org/10.1021/acscatal.8b04707)
