Conformational and structural properties of high functionality dendrimer-like star polymers synthesized from living polymerization techniques

The design, synthesis and solution properties of dendritic-linear hybrid ma cromolecules is described. The synthetic strategy employs living ring-openi ng polymerization in combination with selective and quantitative organic tr ansformations for the preparation of new molecular architectures similar to classical star polymers and dendrimers. The polymers were constructed from high molecular weight poly(epsilon-capiolactone) initiated from the surfac e hydroxyl groups of dendrimers derived from bis(hydroxymethyl) propionic a cid (bis-MPA) in the presence of stannous 2-ethyl hexanoate (Sn(Oct)a). In this way, star and hyperstar poly(epsilon-caprolactones) were elaborated de pending on the generation of dendrimer employed. The ROP from these hydroxy groups was found to be a facile process leading to controlled molecular we ight, low dispersity products (Mw/M-n) < 1.15). In addition to the use of d endrimers as building blocks to star polymers, functional dendrons derived from bis-MPA were attached to chain ends of the star polymers, yielding str uctures that closely resemble that of the most advanced dendrimers. Measure ments of the solution properties (hydrodynamic volume vs, molecular weight) on the dendritic-linear hybrids show a deviation from linearity, with a lo wer than expected hydrodynamic volume, analogous to the solution properties of dendrimers of high generation number. The onset of the deviation begins with the polymers initiated from the second generation dendrimer of bis-MP A and becomes more exaggerated with the higher generations. It was found th at polymerization amplifies the nonlinear solution behavior of dendrimers. Small angle neutron scattering (SANS) measurements revealed that the radius of gyration scaled with arm functionality (f) as f(2/3), in accordance wit h the Daoud-Cotton model for many arm star polymer.