Abstract
Dendrigraft polymers have a multi-level branched architecture resulting from the covalent assembly of macromolecular building blocks. Most of these materials are obtained in divergent (core-first) synthetic procedures whereby the molecule grows outwards in successive grafting reactions or generations. Two main types of dendrigraft polymers can be identified depending on the distribution of reactive sites over the grafting substrate: Arborescent polymers have a large and variable number of more or less uniformly distributed sites, while dendrimer-like star polymers have a lower but well-defined number of grafting sites strictly located at the ends of the substrate chains. An overview of the synthesis and the characterization of dendrigraft copolymers with phase-segregated morphologies is provided in this review for both dendrigraft polymer families. The tethering of side-chains with a different composition onto branched substrates confers unusual physical properties to these copolymers, which are highlighted through selected examples.
Highlights
Different types of macromolecules with well-defined branched architectures have been synthesized over the past 30–40 years including star-branched polymers and polymacromonomers [1,2,3], dendrimers and hyperbranched polymers [4,5], and dendrigraft polymers [4,6,7]
Synthesis of a dendrimer-like star copolymer with a poly(ethylene oxide) core and polystyrene side-chains according to Gnanou et al Variations in the basic method outlined in Scheme 7 have enabled the synthesis of various types of copolymers through analogous grafting from schemes using different branching agents and combinations of anionic, cationic, and atom transfer radical polymerization (ATRP) polymerization techniques
The papers reviewed show that a wide range of heterogeneous dendrigraft copolymer architectures with core-shell and core-shell-corona morphologies can be synthesized, and at a much lower cost than for typical dendrimer syntheses
Summary
Different types of macromolecules with well-defined branched architectures have been synthesized over the past 30–40 years including star-branched polymers and polymacromonomers [1,2,3], dendrimers and hyperbranched polymers [4,5], and dendrigraft polymers [4,6,7]. Dendrigraft copolymers are unimolecular, covalently bonded species with well-defined structures (as opposed to multimolecular or randomly cross-linked assemblies), and branching functionalities ranging from a few to thousands of side-chains, whose basic characteristics (side-chain molecular weight and composition, branching functionality/density, and uniformity) can be accurately controlled in their synthesis These features distinguish them from other heterogeneous macromolecular assemblies such as star-block copolymers with relatively low branching functionalities [11], metastable micelles obtained by the self-assembly of block copolymers in selective solvents [12,13] or stabilized through random cross-linking as in knedel-like structures [14], and core-shell polymer particles prepared by microemulsion polymerization [15,16]. This paper reviews the different methods developed for the synthesis of dendrigraft polymer structures, with emphasis on copolymer systems and the unusual properties arising from these heterogeneous morphologies
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