Molar Mass and Structural Characteristics of Poly[(lactide-co-(aspartic acid)] Block Copolymers IdaPoljansˇek, * Maja Gric ˇar, Ema Z ˇ agar, Majda Z ˇ igon Summary: We report on various synthetic procedures for the preparation of biode- gradable and biocompatible poly(lactide-co-aspartic acid) block copolymers based on natural monomeric units – lactic acid and aspartic acid. Multiblock poly(lactide-co- aspartic acid) copolymers of different comonomer composition were synthesized by heating a mixture of L-aspartic acid and L,L-lactide in melt without the addition of any catalyst or solvent and with further alkaline hydrolysis of the cyclic succinimide rings to aspartic acid units. Diblock poly(lactide-co-aspartic acid) copolymers with different block lengths were prepared by copolymerization of amino terminated poly(b-benzyl- L-aspartate) homopolymer and L,L-lactide with subsequent deprotection of the benzyl protected carboxyl group by hydrogenolysis. The differences in the structure, com- position, molar mass characteristics, and water-solubility of the synthesized multi- block and diblock poly(lactide-co-aspartic acid) copolymers are discussed. Keywords: amphiphiles; biodegradable; block copolymers; drug delivery systems; molar mass distribution; structure Introduction Poly(lactic acid) or poly(lactide) is a biodegradable, biocompatible and bioab- sorbable polyester, which has received much attention in medical, pharmaceutical and packaging applications. [1–10] However, the application scope of poly(lactide) is limited since it is very hydrophobic polymer with no functional groups. In addition, the hydrolytic degradation rate of poly(lactide) for applications for drug delivery purposes is too slow due to its high crystallinity, which results in poorer soft tissue compat- ibility. To overcome the drawbacks of the poly(lactide) homopolymer, many kinds of hydrophilic comonomer units have been incorporated into the poly(lactide) chain. For this purpose many random, block or graft copolymers have been synthesized from hydrophobic lactide and hydrophilic comonomers such as ethylene oxide, capro- lactone, saccharides, amino acids, cellulose, chitosan, etc. [10–24] In our work we focused on biodegrad- able and biocompatible poly(lactide-co- aspartic acid) (PLAA) copolymers, which are promising amphiphilic polymers for drug delivery applications. The copolymers of lactide and aspartic acid were chosen since they combine the advantages of both poly(lactide) and poly(aspartic acid) deri- vatives, and hydrolytically degrade to non- toxic bioabsorbable products. The aspartic acid units with carboxyl functional groups serve as a chelating agent for other substances, and enable solubility of the copolymers in water. Multiblock copolymers of different che- mical composition and with a partially branched structure have been prepared from L,L-lactide and L-aspartic acid in melt without using any catalysts or solvents. [12] Diblock poly(lactide-co-aspartic acid) copo- lymers have been synthesized by copoly- merization of the b-benzyl-L-aspartate-N- Macromol. Symp. 2008, 272, 75–80 DOI: 10.1002/masy.200851210 75 National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia E-mail: ida.poljansek@ki.si Copyright ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim