One‐Step Ring Opening Metathesis Block‐Like Copolymers and their Compositional Analysis by a Novel Retardation Technique

• Published in: Angewandte Chemie International Edition 2020-08, Vol.59 (32), p.13597-13601
• Main Authors: Yasir, Mohammad, Liu, Peng, Markwart, Jens C., Suraeva, Oksana, Wurm, Frederik R., Smart, Jansie, Lattuada, Marco, Kilbinger, Andreas F. M.
• Format: Article
• Language: English
• Subjects: Addition polymerization; Alkylidene; Block copolymers; Catalysts; Consumption; Contamination; Copolymerization; Copolymers; Magnetic resonance spectroscopy; Metathesis; Monomers; NMR; NMR spectroscopy; Nuclear magnetic resonance; olefin metathesis; Ring opening; ring opening metathesis polymerization
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202005366

Using a one‐step synthetic route for block copolymers avoids the repeated addition of monomers to the polymerization mixture, which can easily lead to contamination and, therefore, to the unwanted termination of chain growth. For this purpose, monomers (M1–M5) with different steric hindrances and different propagation rates are explored. Copolymerization of M1 (propagating rapidly) with M2 (propagating slowly), M1 with M3 (propagating extremely slowly) and M4 (propagating rapidly) with M5 (propagating slowly) yielded diblock‐like copolymers using Grubbs’ first (G1) or third generation catalyst (G3). The monomer consumption was followed by 1H NMR spectroscopy, which revealed vastly different reactivity ratios for M1 and M2. In the case of M1 and M3, we observed the highest difference in reactivity ratios (r1=324 and r2=0.003) ever reported for a copolymerization method. A triblock‐like copolymer was also synthesized using G3 by first allowing the consumption of the mixture of M1 and M2 and then adding M1 again. In addition, in order to measure the fast reaction rates of the G3 catalyst with M1, we report a novel retardation technique based on an unusual reversible G3 Fischer‐carbene to G3 benzylidene/alkylidene transformation. Ring opening metathesis polymerization (ROMP) produces block copolymers in one‐step from the mixture of monomers with different steric demand having the highest difference in reactivity ratios ever observed for a copolymerization method. A reversible G3 Fischer‐carbene to G3 benzylidene/alkylidene transformation was used in the compositional analysis of these block copolymers.