​​​Polymerization of Polar Monomers from a Theoretical Perspective​

ABSTRACT: Density functional theory calculations have been used to investigate catalytic mechanism of polymer formation containing polar groups, from the synthesis of the monomer to the synthesis of the macromolecule. In the spirit of a sustainable and green chemistry, we initially focused attention on the coupling of CO₂ as economically convenient and recyclable C1 source with C₂H₄ to form acrylate and/or butirro-lactone, two important polar monomers. In this process formation of a mettallolactone via oxidative coupling of CO₂ and C₂H₄ is an important intermediate. Given this background, we explored in detail (chapter-3) several Ni based catalysts for CO₂ coupling with C₂H₄ to form acrylate. In this thesis we report on the competitive reaction mechanisms (inner vs outer sphere) for the oxidative coupling of CO₂ and ethylene for a set of 11 Ni-based complexes containing bisphosphine ligands. In another effort, considering incorporation of a C=C bond into a metal-oxygen-Functional-Group moiety is a challenging step in several polymerization reactions, we explored the details of this reaction (chapter4) using two different catalysts that are capable to perform this reaction in the synthesis of heterocycles. Specifically, the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-Bis-diphenylphosphino-propane), and the [Pd]/BPh₃ intramolecular alkoxyfunctionalizations. Rest of the thesis we worked on understanding the details of the polymerization of polar monomers using organocatalysts based on N-heterocyclic carbenes (NHC) or N-heterocyclic olefins (NHO). In particular (chapter-5) we studied the polymerization of N-methyl N-carboxy- anhydrides, towards cyclic poly(N-substituted glycine)s, promoted by NHC catalysts. In good agreement with the experimental findings, we demonstrated that NHC promoted ring opening polymerization of N-Me N-Carboxyanhydrides may proceed via two different catalytic pathways. In a similar effort we studied polymerization of propylene oxide (PO) (chapter-6) promoted by N-heterocyclic olefins (NHO) in combination with benzylic alcohol (BnOH). Calculations support the experimental observation that there might be two different catalytic pathways namely the anionic and the zwitterionic pathways. Potential energy surfaces analysis suggested in different NHO one or other mechanism is operational which is strongly depends on steric and electronic properties of particular NHO taken in account.​