Synthesis, Thermal and Mechanical Properties of Linear and Star Poly(L-lactide)s

Poly(L-lactide) with various architectures and molecular weights have been studied with respect to their thermal and mechanical properties. Their synthesis has been performed with an aluminum salen catalyst, which allows to obtain linear chains, tetrahedral 4-arm stars and stars with two linked tetrahedra with 3 arms each, all with defined molecular weights. The polymers are characterized by their molecular weight distributions and then subjected to differential scanning calorimetry and thermogravimetric analyses, which show differences in the characteristic temperatures of not more than 10 degrees. The crystallinity index clearly increases with the weight of the chains with only a minor dependency on the topology. Thin films of the polymers are studied with respect to their elongation at break, their tensile strength, and their moduli. The elongation is most sensitive to the polymer type with a 15-fold increase between the shortest linear polymer and the 6-arm star polymer with the longest chains.