Revealing the Monomer Gradient of Polyether Copolymers Prepared Using <i>N</i>‐Heterocyclic Olefins: Metal‐Free Anionic versus Zwitterionic Lewis Pair Polymerization

N-Heterocyclic olefin (NHO)-based polymerization pathways for the copolymerization of ethylene oxide (EO) and propylene (PO) are investigated in detail. Employing situ 1H NMR spectroscopy, both an organocatalytic, anionic setup (system A) a zwitterionic, Lewis pair-type approach B) studied comparatively. The obtained kinetics data fitted to non-terminal model (Jaacks Ideal Integrated) terminal Mayo–Lewis (Meyer Lowry) determine reactivity ratios, revealing striking differences copolyether microstructure achievable molar masses. While metal-free catalysis ratios rEO = 3.4 rPO 0.30 found, indicating soft gradient structure, presence Mg(HMDS)2 entails exclusively zwitterionic propagation. This results enhanced selectivity, displaying corresponding parameters 7.9 0.13, line with proposed monomer-activated mechanism. block-like, strongly tapered is also reflected thermal properties, showing melting point latter sample much higher masses (Mn >50 000 g mol−1). Notably, this study not only identifies capable systems EO/PO, but underlines that via key questions regarding mechanism can be illuminated quickly reliably, simplifying access essential structure-property relations.