Poly(lactides) with controlled molecular architecture initiated from hydroxyl functional dendrimers and the effect on the hydrodynamic volume

Star poly(lactides) with well defined molecular architectures have been syn thesized from multifunctional dendritic initiators derived from 2,2'-bis(hy droxymethyl)propionic acid (bis-MPA) derivatives. The bis-MPA derivatives, in the presence of stannous 2-ethylhexanoate, generated new polymeric struc tures with accurate control of molecular weight and narrow molecular weight distributions (<1.1). The combination of H-1 NMR and C-13 NMR spectroscopy , and size exclusion chromatography (SEC) showed that all polymers have the requisite structure and the correct number of arms. This allowed character ization of the hydrodynamic volume as a function of molecular weight and nu mber of arms. The results showed a linear relationship of the hydrodynamic volume as a function of the molecular weight for the polymers having two, f our and six arms. However, the star polymers with twelve arms showed a rela tively much smaller hydrodynamic volume, suggesting that these macromolecul es are more globular in their shape. The same effect was found for star pol y(epsilon-caprolactone)s.