Synthesis of symmetric bis-α-ketoamides from renewable starting materials and comparative study of their nucleating efficiency in PLLA

Abstract

An efficient and smart synthesis of bis-α-ketoamides has been disclosed. The desired products have been obtained through a Passerini multicomponent reaction using biobased aldehydes, acetic acid and bis-isocyanides (prepared from the corresponding biobased diamides), followed by a deprotection/oxidation step. The effect of the synthesized compounds on the crystallization behavior of poly(l-lactide) (PLLA) has been investigated by differential scanning calorimetry (DSC) in non-isothermal conditions. Among all the synthesized compounds, only a few are able to meaningfully enhance the nucleation of PLLA, as confirmed by a shift of the polymer crystallization peak temperature towards higher values. With the research of active polymer nucleating agents being mostly empirical, the combinatorial synthetic approach proposed herein, coupled with the possibility of a small scale mixing procedure, can potentially represent a useful strategy for the discovery of new efficient biobased polymer additives.

Fig. 1. General structure of the novel nucleating agents obtained from biobased starting materials.

Scheme 1. Synthesis of bis-α-acetoxyamide 3a.

Fig. 2. (a) DSC cooling curves for PLLA samples containing the molecules reported in Table 1 at a concentration of 1 wt%. Endothermic heat flow direction is upward; (b) measured crystallization peak temperature of PLLA in the different systems. Dashed lines in both (a) and (b) represent the crystallization peak temperature value for pure PLLA. The compound OXA, a known nucleating agent for PLLA is also added at the same concentration, for the sake of comparison.