Synthesis and characterization of polyesteramides having short Nylon-6 segments in the main chains through polycondensation and chain extension

A Nylon-6 oligomer (PrePA) was synthesized by ring-opening polymerization from ε-caprolactam with 2-amino-ethanol under the catalysis of H₃PO₃. Polyesteramide prepolymers (PrePEAs) having amide content from 10 to 60 mol% were prepared through melt polycondensation from adipic acid, 1,4-butanediol and the PrePA. Chain extension of PrePEAs was carried out at 200 °C using 2,2′-(1,4-phenylene)-bis(2-oxazoline) and carbonylbiscaprolactamate as combined chain extenders. The chain-extended polyesteramides (ExtPEAs) with intrinsic viscosity up to 0.61 dL/g were synthesized. The ExtPEAs were characterized by FT-IR and ¹H NMR spectra, differential scanning calorimetry, wide angle X-ray scattering, thermogravimetric analysis and tensile test. The results showed that the ExtPEAs mainly crystallized in the Nylon-6 crystallites. ExtPEAs had T_g from −46.71 to 4.28 °C, T_m from 106.69 to 139.92 °C, thermal stability with initial decomposition temperature over 339 °C, tensile strength up to 30.89 MPa and stain at break higher than 797.1%. These ExtPEAs were strong, thermally stable and tough thermoplastic polymers.