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γ -Amide- ε -caprolactones including 7-oxo- N -propyloxepane-4-carboxamide (NNCL), N -isopropyl-7-oxooxepane-4-carboxamide (NICL), N, N -diethyl-7-oxooxepane-4-carboxamide (DECL), and 5-(pyrrolidine-1-carbonyl)oxepan-2-one (VPyCL) were initially designed and synthesized to achieve biodegradable and thermosensitive materials. Ring-opening polymerization (ROP) of these newly developed caprolactones was thoroughly investigated by both theoretical calculation and experimental verification. Density functional theory revealed that the ring-opening enthalpy of γ-amide-ε-caprolactones was more negative than that of γ -ester- ε -caprolactone (EMCL). Experimental results showed that ROP of NICL, DECL, and VPyCL catalyzed by 1,5,7-triazabicyclo4.4.0dec-5-ene with benzyl alcohol (BnOH) as an initiator underwent in a living and controlled manner, while that of NNCL and EMCL did not. Computational calculation consistently proved that a variety of substitutions greatly affected the ROP process. PNICL, PDECL, and PVPyCL exhibited reversible lower critical solution temperature-type phase transitions tuned by manipulating the feed ratio and hydrophilicity of comonomers. Furthermore, poly( γ -amide- ε -caprolactone)s with excellent biodegradability and biocompatibility were demonstrated as an enzyme activity regulator, holding great promise for smart biomaterial application.
Wen et al. (Wed,) studied this question.