Oxanorbornenes: promising new single addition monomers for the metathesis polymerization

Abstract

Higher ring-opening metathesis propagation rates of <i>exo</i>-norbornene derivatives over <i>endo</i> derivatives are well established in the literature. Here, we report for the first time that <i>endo</i>-isomers of oxanorbornene derivatives show higher reactivity towards ring-opening metathesis with Grubbs' 3rd generation catalyst (<b>G3</b>) than the corresponding <i>exo</i>-isomers. A very high selectivity for the reaction of <b>G3</b> with <i>endo</i> over the <i>exo</i>-isomers could be shown. Furthermore, single molecular addition of the <i>endo</i>-isomers with <b>G3</b> was observed. On the other hand, pure <i>exo</i>-monomers could successfully be homopolymerized. Mixtures of <i>exo</i>- and <i>endo</i>- monomers, however, prevented the homopolymerization of the <i>exo</i>-monomer. Such mixtures could successfully be copolymerized with cycloalkenes, resulting in alternating copolymers. An oxanorbornadiene derivative could be shown to undergo single addition reactions, exploited in the preparation of mono-end functional ROMP polymers. These could be selectively derivatized <i>via</i> endgroup selective thiol-ene click reactions. A thiol and alcohol end functional ROMP polymer was synthesized, and the efficient end functionalization was confirmed by ¹H NMR spectroscopy and MALDI-ToF spectrometry.