Preparation and Structural Characteristics of Multiblock and Diblock Poly(L,L-Lactide-co-L-Aspartic Acid) Copolymers

Maja Gričar, Ida Poljanšek, Blaž Brulc, Tina Šmigovec, Majda Žigon and Ema Žagar*

National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
* Corresponding author: ema.zagar@ki.si

Abstract
In this study we present the preparation of amphiphilic multiblock and diblock poly(L,L-lactide-co-L-aspartic acid) (PLAA) copolymers of different comonomer composition as well as the differences in their structural and molar mass characteristics. Multiblock PLAA copolymers were prepared by heating a mixture of L-aspartic acid and L,L-lactide in melt without additional catalysts, whereas the diblock PLAA copolymers were synthesized by copolymerization of the amino terminated poly(β-benzyl L-aspartate) homopolymer and L,L-lactide in THF/dioxane solution. The differences in structure, composition and molar mass characteristics of poly(L,L-lactide-co-L-aspartic acid) copolymers prepared according to the described synthetic procedures are discussed. The PLAA copolymers synthesized in melt are multiblock copolymers with partially branched structure, whereas those synthesized in solution are linear diblock copolymers with well defined length of both blocks. Both copolymers have comparable molar mass averages in the range of 10³–10⁴ g/mol, but they differ in molar mass distribution, which is narrower for diblock copolymers.

Keywords: Polyester, biodegradable, block copolymers, ring opening polymerization, molar mass distribution