Nano aggregates of biodegradable amphiphilic poly(hydroxyethyl aspartamide-co-propyl aspartamide) grafted with poly(d,l-lactide)

Amphiphilic graft copolymers composed of poly(hydroxyethyl aspartamide)-co-propyl aspartamide) (PHEA-PA) as the hydrophilic backbone and poly(lactide) (PLA) as the hydrophobic side chain were successfully synthesized by grafting lactide (LTD) onto PHEA-PA. Polysuccinimide (PSI) was firstly synthesized from l-aspartic acid through thermal condensation polymerization method, and then followed by two-step aminolysis processes to form PHEA-PA with different amounts of hydroxyl groups. The hydroxyl groups were then used as initial points to graft PLA onto PHEA-PA backbone via a ring-opening polymerization in the presence of Sn(Oct)2. The grafting reaction of PLA onto PHEA-PA was confirmed by 1H NMR, FT-IR, and DSC. Micelle-like aggregates were obtained when the amphiphilic comb-like copolymer solution of DMF was added into an excessive amount of water. Strong hydrophobic intramolecular and intermolecular association of PLA chains led to aggregates with hydrophobic microdomains. The dispersion of the self-aggregates of poly(hydroxyethyl aspartamide-co-propyl aspartamide)-g-poly(d,l-lactide) (PHEA-PA-g-PLA) copolymers is stable in aqueous medium. Spherical aggregates of PHEA-PA-g-PLA were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), the diameters were about 100 nm.