Regulation of ester contents enabled tunable thermal and mechanical properties of poly(ester amide)

Poly(ε-caprolactone-co-ε-caprolactam) was synthesized through ring-opening copolymerization of ε-caprolactone (CLO) and ε-caprolactam catalyzed by ethylmagnesium bromide (EtMgBr) or sodium ε-caprolactam. Varied ester contents were achieved from 0 to 100 mol%. EtMgBr enabled the copolymerization with high yield of over 95%. Thermal properties vary with different ester contents. With increasing CLO content, the onset decomposition temperature (273.36 to 240.97 °C) and glass transition temperature (52.1 to −56.3 °C) gradually decreased. The results of melting behavior of resultant poly(ester amide)s through differential scanning calorimetry and theoretical calculation indicated a eutectic temperature of 46.6 °C. The mechanical properties of obtained copolymers were systematically investigated. The enhancement of CLO incorporation led to a decrease in tensile strength (70.99 to 9.88 MPa) and Young's modulus (690.03 to 19.18 MPa). Copolymer with CLO incorporation of 70 mol% exhibited a eutectic temperature of 46.6 °C, and enabled a high elongation at break (658%) and enhanced impact strength (138.5 kJ m⁻²).