A new type of macromolecular architecture, denoted as dendrimer-like star block copolymers, is reported. These block copolymers are described by a radial geometry where the different generations or layers are comprised of high molecular weight polymer emanating from a central core. A hexahydroxyl functional core was used as an initiator for the “living” ring opening polymerization (ROP) of ε-caprolactone producing a hydroxyl terminated six arm star polymer with controlled molecular weight and narrow polydispersities (PD < 1.1). Capping these chain ends with dendrons containing activated bromide moieties produced “macro-initiators” for atom transfer radical polymerization (ATRP). Methyl methacrylate was polymerized from these “macro-initiators” in the presence of an organometallic promoter to produce the requisite dendrimer-like star polymers. High molecular weight was obtained with low polydispersities (<1.2). Alternatively, amphiphilic character could be introduced by designing the different layers or generations to be either hydrophobic or hydrophilic. For example, methyl methacrylate (MMA) with either hydroxyethyl methacrylate (HEMA) or methacrylate functional ethylene oxide macromonomers (EO) were polymerized from these “macro-initiators” to provide a hydrophilic outer layer. The use of macromolecular building blocks allows rapid attainment of high polymer in a limited number of steps with purification between transformation requiring only polymer precipitation.

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 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.

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