Enhancing the properties of poly(propylene succinate) by the incorporation of crystallizable symmetrical amido diols

Poly(ester amide)s derived from succinic acid with sufficient degree of polymerization cannot be obtained by common synthetic routes since the formation of cyclic imide structures is favored in the reaction of succinic acid with primary amines. Herein, a straightforward synthetic strategy is applied to synthesize poly(ester amides) from succinic acid which relies on amido diol building blocks. By application of these symmetrical diols that have two internal amide bonds, the formation of chain-terminating N-succinimide end groups could be almost completely suppressed. The poor thermal and mechanical properties of poly(propylene succinate) were significantly improved by the insertion of varying amounts of ester amide segments. Tg and Tm could be enhanced from −33 to −6 °C and 41 to 155 °C, respectively. Furthermore, crystallization from the melt was considerably accelerated with rising amido diol content while the typical crystalline phase of polyamides was found. Correspondingly, the stiffness of the polymers increased notably. The poly(ester amide)s showed high biodegradation rates up to an ester amide fraction of 25 mol%.