Dendrimer-like Star Polymers

Abstract

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 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 1 H and 13 C 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.