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, i nterfacial properties, and aggregate formation. The polymers were synthesiz ed by thermal condensation and aminolysis by alkylamine, followed by hydrol ysis of the remaining succinimide units in the polymer backbone. The polyme rs formed self-aggregates by ultrasonication. Strong hydrophobic interactio n by a higher amount of grafted alkyl chains induced higher aqueous stabili ty of the self-aggregates. Bending of the stiff PASP backbone and strong as sociation of alkyl chains were considered to be major competitive factors f or determining aqueous stability. An aqueous solution of PASP-C18 was not s urface-active due to physical cross-linker nature of octadecyl chains, whil e dodecyl and hexadecyl chains with higher chain flexibility showed surface -active properties. CAC calculated from fluorescence excitation spectra sho wed logarithmically decreasing behavior as DS of alkyl chains.