Cross-Metathesis and Hydrogenation in Polynorbornene–Poly(5-hydroxyoctenamer) Mixture in the Presence of Grubbs’ Catalysts
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An exchange reaction of cross-metathesis between polynorbornene and poly(5-hydroxyoctenamer) in a chloroform–methanol mixture (10: 1 vol/vol) in the presence of Ru–carbene Grubbs’ complexes Gr-1 and Gr-2 has been studied. Gr-2 catalyst has a much higher activity and allows one to obtain multiblock copolymers, which cannot be synthesized directly from norbornene and 5-hydroxy-1-cyclooctene. The average length of the copolymer blocks varies in a wide range depending on the reaction conditions. The individual stages of the process have been studied with the use of in situ monitoring of transformations of Ru–carbene complexes by 1Н NMR spectroscopy and ex situ analysis of heterodyad evolution in copolymers via 13C NMR spectroscopy. As has been shown, poly(5-hydroxyoctenamer) forms Ru–carbene complexes with the catalyst more easily than polynorbornene; in this case, the incorporation of a substituent in the monomer unit of octenamer retards the polymer cross-metathesis. It has been found that, in systems containing Gr-2 and hydroxyoctenamer blocks, the formed ruthenium hydride complexes initiated hydrogenation process. The hydrogenation results in the appearance of crystallinity in the initially amorphous polymers, which opens up the possibilities for the targeted control of the multiblock copolymers properties.
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