Dendrimer-like star polymers

Dendrimer-like star polymers, a novel type of molecular architecture, have been synthesized. The architecture of the new polymers resembles that of three-dimensional spherical dendrimers as well as classical star polymers. The controlled structures, based on aliphatic polyesters, are synthesized by a divergent growth approach. A hexa hydroxy-functional 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) derivative was used as the "initiator" for the stannous-2-ethylhexanoate (Sn(Oct)(2)) catalyzed living ring opening polymerization of epsilon-caprolactone. The polymerization generated a six-arm polymer with a molecular weight of 14 300 (M-n) and a M-w/M-n of 1.06. The new polymer was functionalized with a protected bis-MPA, deprotected, and used as the "macroinitiator" for the polymerization of a second generation 12 armed poly(epsilon-caprolactone) (M-n = 42 300, M-w/M-n = 1.16). Another iteration of the same procedure generated a third generation 24 arm dendrimer-like star polymer with a M-n of 96 000 and M-w/M-n of 1.14. The complete initiation and functionalization was carefully investigated by H-1 and C-13 NMR. These novel polymers are different from traditional dendritic materials in that this synthetic strategy allows these well defined highly branched polymers to reach a high molecular weight in only a few steps. In addition these materials are semicrystalline.