ABSTRACT
Arborescent polymers are characterized by a tree-like or dendritic structure resulting from successive anionic grafting reactions. Synthetic routes to different types of well-defined arborescent homo- and copolymers with branching functionalities fw ≈ 10 to over 10 000 and weight-average molecular weights Mw ≈ 5 × 104−108 are discussed in this review. Styrene homopolymers with an arborescent structure are obtained in high yield by first coupling 1,1-diphenylethylene-capped polystyryl anions with a linear chloromethylated polystyrene substrate. The resulting comb-branched (generation G0) polymer is further chloromethylated and grafted with polystyryl anions to yield a G1 aborescent polystyrene, and so on. The synthetic method used for arborescent polystyrenes can be extended to the preparation of branched copolymers using both grafting onto and grafting from schemes. Polyisoprene, poly(2-vinylpyridine), and poly(tert-butyl methacrylate) copolymers can be prepared by direct coupling of the corresponding living anions with a suitably functionalized arborescent polystyrene grafting substrate (grafting onto method). It is also possible to synthesize copolymers containing poly(ethylene oxide), polydimethylsiloxane or polycaprolactone segments end-linked to the substrate chains using arborescent polystyrenes end-functionalized with hydroxyl groups as polyfunctional initiators (grafting from method). The physical properties of arborescent polymers in solution, in the molten and solid states more closely resemble those of hard spheres as the branching functionality increases, in particular for shorter side chains. Some specific examples of the unusual physical properties exhibited by arborescent polymers making them interesting for specialty applications are discussed.
