Effects of grafted alkyl groups on aggregation behavior of amphiphilic poly(aspartic acid)

The aggregation behavior of biodegradable amphiphilic poly(aspartic acid) (PASP) derivatives containing long alkyl chains was characterized by size, interfacial properties, and aggregate formation. The polymers were synthesized by thermal condensation and aminolysis by alkylamine, followed by hydrolysis of the remaining succinimide units in the polymer backbone. The polymers formed self-aggregates by ultrasonication. Strong hydrophobic interaction by a higher amount of grafted alkyl chains induced higher aqueous stability of the self-aggregates. Bending of the stiff PASP backbone and strong association of alkyl chains were considered to be major competitive factors for determining aqueous stability. An aqueous solution of PASP-C18 was not surface-active due to physical cross-linker nature of octadecyl chains, while dodecyl and hexadecyl chains with higher chain flexibility showed surface-active properties. CAC calculated from fluorescence excitation spectra showed logarithmically decreasing behavior as DS of alkyl chains.