Nanocomposites of polyethylene with polyhedral oligomeric silsesquioxane: from thermoplastics to vitrimers through silyl ether metathesis

In this contribution, we reported the transformation of linear polyethylene-polyhedral oligomeric silsesquioxane (PE-POSS) copolymers into PE vitrimers through silyl ether metathesis. First, the PE-POSS copolymers were synthesized via the ring-opening metathesis polymerisation (ROMP) of cyclooctene with heptaisobutyl POSS-norbornene followed by subsequent hydrogenation reaction. The PE-POSS copolymers were microphase -separated, and the POSS cages were aggregated into the microdomains with the size of 10–20 nm. The thermoplastic PE-POSS nanocomposites were transformed into the PE vitrimers via direct silyl ether metathesis, which was catalyzed with zinc trifluoromethyl sulfonate Zn(OTf)₂]. It was found that the cross-linking with the dynamic covalent bonds occurred within the POSS microdomains. The cross-linking significantly influenced the morphologies and thermal and mechanical properties of the materials. More importantly, the cross-linked PE products displayed the self-adaptivity at elevated temperature, that is, the PE-POSS thermoplastics were transformed into PE-polysilsesquioxane vitrimers. Because of the formation of cross-linked networks, the PE vitrimers were endowed with shape memory properties. In the meantime, the permanent shapes of the shape memory PEs can readily be reprogrammed by taking advantage of the self-adaptivity of the vitrimers.