Abstract
Dendrimer-like star polymers, a novel type of molecular architecture, have been synthesized. The architecture of the new polymers resembles that of thee-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 ε-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(ε-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 1H and 13C 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.