Synthesis of core-shell bottlebrush polymers of poly(polycaprolactone-b-polyethylene glycol) via ring-opening metathesis polymerization

This research was focused on the synthesis of core-shell bottlebrush polymer poly(PCL-b-PEG) (PCL: polycaprolactone; PEG: polyethylene glycol) through a combination of ring-opening polymerization (ROP) and ring-opening metathesis polymerization (ROMP). Three main steps were involved in this synthesis: firstly, the ROP of ε-caprolactone was conducted to form an amphiphilic linear polymer PEG-b-PCL in presence of methoxypolyethylene glycols and Sn(Oct)2; secondly, macromonomers with norbornenyl-functionalization were synthesized by the esterification of the hydroxyl-terminated PEG-b-PCL with 5-norbornene-2-carboxylic acid; thirdly, the synthesized macromonomers were further polymerized by ROMP in presence of Grubbs second-generation catalyst to form a core-shell bottlebrush structured polymer. The effects of the reaction time, concentrations of small-molecule monomers, amount of catalyst and the molecular weights of macromonomers on the performance of the ROMP of the macromonomers were investigated in detail. 1H NMR and GPC analyses confirmed the structures of the resulting polymers. DSC, XRD, TGA were used to characterize the properties of PEG-b-PCL and poly(PCL-b-PEG). Compared with the linear block polymers PEG-b-PCL, the resulting polymers with core-shell bottlebrush structures have a more regular chain arrangement and better thermal stability.