Synthesis and solvent-controlled self-assembly of diketopiperazine-based polyamides from aspartame

An aspartame-based AB-type diketopiperazine monomer, cyclo(l-aspartyl-4-amino-l-phenylalanyl) (ADKP), was synthesized and subsequently utilized in the polycondensation of homo-polyamides with high molecular weights. By using various amino acids, dicarboxylic acids, and diamines, random DKP-based copolymers were also synthesized. The self-assembly properties of ADKP and poly(cyclo(l-aspartyl-4-amino-l-phenylalanyl)) (PA1) were studied via the solvent displacement method. Notably, PA1 self-assembled into particles with various morphologies in different solvent systems, such as irregular networks, ellipsoids, and hollow particles. The morphological transformation was also confirmed by dropping acetone and toluene onto the PA1 particles. Furthermore, infrared spectra and Hansen solubility parameters of PA1 and different solvents revealed the particle formation mechanism, which provided more insights into the relationship between the morphology and strength of the hydrogen bonding of each solvent.