Dendrimer-like star block and amphiphilic copolymers by combination of ring opening and atom transfer radical polymerization

A new type of macromolecular architecture, denoted as dendrimer-like star b lock copolymers, is reported. These block copolymers are described by a rad ial geometry where the different generations or layers are comprised of hig h molecular weight polymer emanating from a central core. A hexahydroxyl fu nctional core was used as an initiator for the "living" ring opening polyme rization (ROP) of epsilon-caprolactone producing a hydroxyl terminated six arm star polymer with controlled molecular weight and narrow polydispersiti es (PD < 1.1). Capping these chain ends with dendrons containing activated bromide moieties produced "macro-initiators" for atom transfer radical poly merization (ATRP). Methyl methacrylate was polymerized from these "macro-in itiators" in the presence of an organometallic promoter to produce the requ isite 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 h ydrophobic or hydrophilic. For example, methyl methacrylate (MMA) with eith er hydroxyethyl methacrylate (HEMA) or methacrylate functional ethylene oxi de macromonomers (EO) were polymerized from these "macro-initiators" to pro vide a hydrophilic outer layer. The use of macromolecular building blocks a llows rapid attainment of high polymer in a limited number of steps with pu rification between transformation requiring only polymer precipitation.