We present a systematic, thermal study on the synthesis of poly(ester amide)s (PEAs) by the melt condensation of citric acid (CA), D-glucono-δ-lactone (GL) and various amino acids (AAs). The reactions were studied by differential scanning calorimetry (DSC) and it was found that the incorporation of amino acids into the previously investigated CA/GL system (de Jongh et al., 2017) results in a significant increase of the glass transition temperature (Tgs) of the resulting PEAs as a result of the introduction of amide bonds. AAs with functional side chains (i.e. hydroxyl, thiol, carboxylic acid or amine) resulted in higher Tgs than AAs with hydrophobic, non-reactive side chains, which is attributed to additional crosslinking in the PEAs. The copolymerisation of proline (and two structural analogues), despite having no reactive side chain, yielded PEAs with significantly higher Tgs than any other AA as a result of its cyclic structure.
- Amino acid
- Citric acid
- Differential scanning calorimetry
- Poly(ester amide)
- Renewable materials