Synthesis of Dendrimer-Like Polymers

Abstract

This chapter reviews the synthesis of dendrimer-like polymers based on controlled or living polymerization techniques. Dendrimer-like polymers possess multiple chains interconnected in a dendritic way. The synthetic strategies include divergent and convergent methods, as those for regular dendrimers, in combination with the preparation of the polymer chains either in situ or in separate batches. The divergent approach usually starts from a core with multifunctional initiation or coupling reaction sites, followed by iterative polymerization/chain-end functionalization, or grafting-to reaction/end-group transformation of the upcoming polymer chains, respectively, to form dendrimer-like polymers of up to seventh generation. The convergent approach involves efficient coupling reactions, such as reaction between chlorosilane and living polymeric anion, and the reactivation of the joint point into living anion in an alternating way. The latter suffers from more serious steric hindrance than the former. A variety of dendrimer-like polymers, such as poly (ethylene oxide) (PEO), polystyrene (PS), poly(meth)acrylates, polycaprolactone (PCL), and their related copolymers, have been reported in the literature. The control of molecular parameters of dendrimer-like products will be discussed in the synthetic point of view.

Thermally Responsive Unimolecular Nanoreactors from Amphiphilic Dendrimer-Like Copolymer Prepared via Anionic Polymerization and Cross Metathesis Reaction

“…Dendrimer-like polymers are a unique class of dendrimers in which the branch points of successive generations are interlinked with polymer segments. − They exhibit molecular structure similar to regular dendrimers, , such as the presence of a central core and multiplicity of branch points and terminal functionalities, yet are more tunable on the molecular level to further affect their properties, including chemical composition of polymer segments, number of peripheral functional groups, density of branching, size of the molecules and the interior cavity . For example, the molecular weight of dendrimer-like polymers can be as high as tens of millions at medium generations, resulting in diameters of up to tens of nanometers, which is remarkably larger than the regular dendrimers. − Thus, dendrimer-like polymers covers a wider range of sizes, which would be beneficial for the application as functional materials.…”

“…For example, the molecular weight of dendrimer-like polymers can be as high as tens of millions at medium generations, resulting in diameters of up to tens of nanometers, which is remarkably larger than the regular dendrimers. − Thus, dendrimer-like polymers covers a wider range of sizes, which would be beneficial for the application as functional materials. The synthesis of dendrimer-like polymer has been performed either through divergent or convergent method, among which the former being dominant due to significant steric hindrance in the latter. ,, In the divergent method, the polymer segment can be formed either by “grow-from” or “attach-to” approaches, depending on the polymerization mechanism, i.e., usually atom transfer radical polymerization (ATRP), ring opening polymerization, or living anionic polymerization. − Particularly, amphiphilic dendrimer-like copolymers with layered structures were synthesized by introducing hydrophobic segment, such as poly­(styrene) and poly­( l -lactide) (PLLA), and hydrophilic segment such as poly­(ethylene oxide) (PEO), poly­(acrylic acid) (PAA), poly­(2-vinylpyridine) (P2VP), and poly­( p -hydroxylstyrene). ,,− These amphiphilic dendrimer-like copolymers can be used as unimolecular micelles as demonstrated by a number of studies. − Nevertheless, they have never been used as nanoreactors for organic reactions.…”

“…The synthesis of dendrimerlike polymer has been performed either through divergent or convergent method, among which the former being dominant due to significant steric hindrance in the latter. 25,26,29 In the divergent method, the polymer segment can be formed either by "grow-from" or "attach-to" approaches, depending on the polymerization mechanism, i.e., usually atom transfer radical polymerization (ATRP), ring opening polymerization, or living anionic polymerization. 35−37 Particularly, amphiphilic dendrimer-like copolymers with layered structures were synthesized by introducing hydrophobic segment, such as poly-(styrene) and poly(L-lactide) (PLLA), and hydrophilic segment such as poly(ethylene oxide) (PEO), poly(acrylic acid) (PAA), poly(2-vinylpyridine) (P2VP), and poly(p-hydroxylstyrene).…”