Random and quasi-alternating polyesteramides deriving from ε-caprolactone and β-alanine

A series of random polyesteramides (PEAs) were obtained by direct reaction of ε-caprolactone and β-alanine in the melt and a quasi-alternating polyesteramide (degree of randomness = 1.63) was synthesized by melt polycondensation of an intermediate hydroxy- and ethyl ester-terminated amide. Model reactions show that the reaction between ε-caprolactone and β-alanine proceeds first by the ring opening of ε-caprolactone by the amine groups of β-alanine. The random PEAs with ε-caprolactone contents equal to or higher than 60 mol.% present a well-defined endotherm (Tm = 29–56 °C) corresponding to CL-rich polymer domains. On the other hand, random PEAs with ε-caprolactone content below 60 mol.% present a broad melting zone (Tm = 133–159 °C) corresponding to ill-defined β-Ala-rich polymer domains. The quasi-alternating PEA (ε-caprolactone content of 50 mol.%) presents a well-defined and large melting endotherm (Tm = 92 °C) and exhibits notably higher Young’s modulus and ultimate tensile strength than its random counterpart.