Organocatalyzed ring-opening graft copolymerization of cyclic esters from Poly(2-hydroxyethyl vinyl ether-ran-vinyl acetate): Synthesis and thermal properties

The synthesis of novel graft copolymers with poly(ε-caprolactone) (PCL) side chains using poly(2-hydroxyethyl vinyl ether-ran-vinyl acetate) [P(HEVE-ran-VAc)] as the main chain is reported. P(HEVE-ran-VAc) is synthesized via RAFT radical copolymerization, followed by quantitative ring-opening polymerization of ε-caprolactone (CL) from the hydroxy groups using the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) organocatalyst. This approach produces P(HEVE-ran-VAc)-g-PCL with precisely controlled side chain lengths and densities. The structure–property relationships are thoroughly investigated, revealing dual thermal transitions from the amorphous main chain and semicrystalline PCL side chains. The P(HEVE-ran-VAc) main chain effectively reduces PCL crystallinity to 37-42%, which is attributed to the constraints imposed by the amorphous main chain on the crystallization of the PCL side chains. Crystallinity increases with longer side chain lengths or higher side chain densities, and thermal stability correlates with crystallinity levels, with higher crystallinity resulting in improved thermal resistance. Differential scanning calorimetry and thermogravimetric analyses confirm these structure–property relationships. The versatility of this approach is further demonstrated by extending it to other cyclic esters, including L-lactide and δ-valerolactone (VL), enabling the synthesis of complex architectures containing poly(δ-valerolactone) (PVL), such as P(HEVE-ran-VAc)-g-(PCL-b-PVL).