Macromolecular cross-metathesis offers a top-down approach fusing polyolefin homopolymers to multiblock copolymers

Ring-opening metathesis polymerization (ROMP) followed by hydrogenation has been widely used to prepare semicrystalline polyolefins. Hydrogenation of poly(cis -cyclooctene) (PCOE) affords perfect linear polyethylene (LPE) while hydrogenated polynorbornene (hPNB), regardless of tacticity, exhibits a high degree of crystallinity. Multiblock polyolefins can usually be synthesized by sequential monomer addition as a bottom-up method, building from polymerizable units. However, synthesis of LPE/hPNB multiblock copolymers (MBCs) is challenging because their PCOE/PNB precursor copolymers cannot be synthesized directly from monomers, as secondary metathesis of the unhindered double bonds in PCOE chains results in an uncontrolled polymer architecture. Here, we report a top-down approach that is the interchain cross-metathesis between PCOE and PNB homopolymers to achieve PCOE/PNB MBCs. Interchain cross-metathesis of PCOE and PNB homopolymers enables segment exchange, yielding PCOE/PNB MBC precursors with block lengths tunable by reaction efficiency. Hydrogenation affords LPE/hPNB MBCs, and thermal/structural analysis verifies distinct semicrystalline morphologies and successful fusion of LPE and hPNB homopolymers into LPE/hPNB MBCs.