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 epsilon-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. H-1 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.

Automated summary

This research successfully synthesized core-shell bottlebrush polymer poly(PCL-b-PEG) with a more regular chain arrangement and better thermal stability compared to linear block polymers.