Well-Defined Poly(α-amino-δ-valerolactone) via Living Ring-Opening Polymerization

This article demonstrates the synthesis of a new kind of cationic poly(δ-valerolactone) with primary amino groups at α-positions (poly(α-NH2-VL)) via ring-opening polymerization (ROP) of α-NHBoc-valerolactone (α-NHB-VL) followed by a simple deprotection reaction. The ROP of α-NHB-VL using benzyl alcohol as an initiator and DBU/TU (1,8-diazabicyclo[5.4.0]undec-7-ene/thiourea) as a catalytic system in THF at room temperature afforded poly(α-NHB-VL) with narrow molecular weight distribution. The 1H NMR and MALDI-TOF MS analysis of poly(α-NHB-VL) indicated that each polymeric chain was capped by the initiator. Kinetic experiments confirmed the living nature of the DBU/TU-catalyzed ROP of α-NHB-VL in THF. The copolymerization result indicated that the polymerization activity of α-NHB-VL is comparable to that of ε-caprolactone (CL) and VL. In addition, block copolymers containing poly(α-NHB-VL) were successfully synthesized regardless of whether hydrophilic PEG or hydrophobic PCL was used as the macroinitiator. Moreover, water-soluble poly(α-NH2-VL) was obtained by treatment with trifluoroacetic acid (TFA). It was found that poly(α-NH2-VL) degraded more slowly at pH 5.5 than at pH 7.4 through a hydrolysis kinetics study.