Binary catalytic system for homo- and block copolymerization of ε-caprolactone with δ-valerolactone

The combined interaction of 2,3,6,7-tetrahydro-5H-thiazolo[3,2-a] pyrimidine (ITU) as the organocatalytic nucleophile with YCl(3) as Lewis acid cocatalyst, generating ITU/YCl(3), was employed for homo- and copolymerization of ε-caprolactone (CL) with δ-valerolactone (VL). Poly(caprolactone) (PCL) and poly(caprolactone)–poly(ethylene glycol)–poly(caprolactone) (PCL–PEG–PCL) triblock copolymer and poly(valerolactone)–poly(caprolactone)–poly(ethylene glycol)–poly(caprolactone)–poly(valerolactone) (PVL–PCL–PEG–PCL–PVL) pentablock copolymer were successfully prepared by ring-opening polymerization (ROP) of CL employing ITU/YCl(3) as catalyst in the presence of benzyl alcohol (BnOH) or poly(ethylene glycol) (PEG) as initiator, respectively. The reaction was systematically optimized, and the architecture, molecular weight and thermal properties of the polymers were characterized by NMR, FTIR, SEC and DSC analyses. Finally, a plausible polymerization mechanism was proposed.