Synthesis and characterization of high grafting density bottle-brush poly(oxa)norbornene-g-poly(ε-caprolactone)

Abstract

Poly(ε-caprolactone)-based (oxa)norbornene macromonomers with two poly(ε-caprolactone) (PCL) chains on the polymerizable entity were synthesized through organocatalyst mediated ring-opening polymerization (ROP) in high yields, with excellent control over molecular weights (from 2800 to 11 000 g mol⁻¹) and dispersities (Đ_M < 1.26). Ring-opening metathesis polymerization (ROMP) of these macromonomers was carried out using the very active, fast-initiating Grubbs’ second generation catalyst and the fast-initiating, fast-propagating Grubbs’ third generation catalyst. High grafting density poly(oxa)norbornene-g-PCLs were obtained with a backbone length between 10 and 100 repeating units and a graft length between 10 and 48 while retaining a narrow distribution of molecular weights, leading to comb or brush copolymers according to the lengths of the backbone and graft chains. Thermal analyses show a higher stability of the bottle-brush poly(oxa)norbornene-g-PCLs compared to their PCL-based (oxa)norbornene macromonomers together with a weaker crystallinity resulting from steric hindrance.