and Stockmayer [33, 34]. In 1943, Flory introduced the term “network cell,” which
he defined as the most fundamental unit in a molecular network structure [35]. To
paraphrase the original definition, it is the recurring branch juncture in a network
system as well as the excluded volume associated with this branch juncture.
Graessley [36] took the notion one step further by describing ensembles of these
network cells as micronetworks. Extending the concept of Flory’s statistical treatment of Gaussian-coil networks, analogous species that are part of an open,
branched or dendritic organization are known as “branch cells” and “dendritic
assemblies.”
Statistical modeling by Gordon et al. [37, 38], Dusek [39], Burchard [40] and
others reduced such branched species to graph theory designed to mimic the
morphological branching of trees. These dendritic models were combined with
cascade theory [41, 42] mathematics to give a reasonable statistical treatment for
network-forming events at that time.
The growth of branched and dendritic macromolecules in the sol phase of a
traditional crosslinking process may be thought of as geometric aggregations of
various branch cells or dendritic (network) assemblies, as described above. Beginning as molecular species, they advance through the dimensional complexity
hierarchy to oligomeric, macromolecular, megamolecular, and ultimately to infinite
network macroscale systems. The intermediacy of dendritic architecture in this
continuum will be discussed later (Sect. 3.2). Traditional network-forming systems
(e.g., epoxy resins, urethanes, polyesters) progress through this growth process in a
statistical, random fashion. The resulting infinite networks may be visualized as a
collection of unequally segmented Gaussian chains between f-functional branch
junctures, crosslinks (loops), and dangling terminal groups.
More recently, non-traditional polymerization strategies have evolved to produce a fourth new major polymer architectural class, now referred to as “dendritic
polymers” [43]. This new architectural polymer class consists of four major subsets: (1) random hyperbranched, (2) dendrigrafts, (3) dendrons and (4) dendrimers.
Dendrimers, the most extensively studied subset were discovered by the Tomalia
group while in The Dow Chemical Company laboratories (1979) and represent the
first example of synthetic, macromolecular dendritic architecture [43, 44]. First use
of the term “dendrimer” appeared in preprints for the first SPSJ International
Polymer Conference, held in Kyoto, Japan in 1984 [45]. The following year, a
full article in Polymer Journal [46] (Fig. 8) described the first preparation of a
complete family of Tomalia-type poly(amidoamine) (PAMAM) dendrimers
(G ¼ 1–7) and their use as precise, fundamental building blocks to form poly
(dendrimers) or so-called “starburst” polymers. These poly(dendrimers) are now
referred to as “megamers” [47, 48] and are described in more detail later in
Sect. 6.4.3. Other pioneers in the dendritic polymer field include Vogtle, Newkome,
Frechet, Majoral, and others. These historical contributions have been reviewed
recently [52] .
This article will overview the dendritic architectural state, its unique architecturally driven properties, its role relative to traditional polymer science, and
describe the many enabling features that dendrimers are expected to offer to the
emerging nanotechnology revolution.
Twenty-First Century Polymer Science After Staudinger: The Emergence of. . .
333
he defined as the most fundamental unit in a molecular network structure [35]. To
paraphrase the original definition, it is the recurring branch juncture in a network
system as well as the excluded volume associated with this branch juncture.
Graessley [36] took the notion one step further by describing ensembles of these
network cells as micronetworks. Extending the concept of Flory’s statistical treatment of Gaussian-coil networks, analogous species that are part of an open,
branched or dendritic organization are known as “branch cells” and “dendritic
assemblies.”
Statistical modeling by Gordon et al. [37, 38], Dusek [39], Burchard [40] and
others reduced such branched species to graph theory designed to mimic the
morphological branching of trees. These dendritic models were combined with
cascade theory [41, 42] mathematics to give a reasonable statistical treatment for
network-forming events at that time.
The growth of branched and dendritic macromolecules in the sol phase of a
traditional crosslinking process may be thought of as geometric aggregations of
various branch cells or dendritic (network) assemblies, as described above. Beginning as molecular species, they advance through the dimensional complexity
hierarchy to oligomeric, macromolecular, megamolecular, and ultimately to infinite
network macroscale systems. The intermediacy of dendritic architecture in this
continuum will be discussed later (Sect. 3.2). Traditional network-forming systems
(e.g., epoxy resins, urethanes, polyesters) progress through this growth process in a
statistical, random fashion. The resulting infinite networks may be visualized as a
collection of unequally segmented Gaussian chains between f-functional branch
junctures, crosslinks (loops), and dangling terminal groups.
More recently, non-traditional polymerization strategies have evolved to produce a fourth new major polymer architectural class, now referred to as “dendritic
polymers” [43]. This new architectural polymer class consists of four major subsets: (1) random hyperbranched, (2) dendrigrafts, (3) dendrons and (4) dendrimers.
Dendrimers, the most extensively studied subset were discovered by the Tomalia
group while in The Dow Chemical Company laboratories (1979) and represent the
first example of synthetic, macromolecular dendritic architecture [43, 44]. First use
of the term “dendrimer” appeared in preprints for the first SPSJ International
Polymer Conference, held in Kyoto, Japan in 1984 [45]. The following year, a
full article in Polymer Journal [46] (Fig. 8) described the first preparation of a
complete family of Tomalia-type poly(amidoamine) (PAMAM) dendrimers
(G ¼ 1–7) and their use as precise, fundamental building blocks to form poly
(dendrimers) or so-called “starburst” polymers. These poly(dendrimers) are now
referred to as “megamers” [47, 48] and are described in more detail later in
Sect. 6.4.3. Other pioneers in the dendritic polymer field include Vogtle, Newkome,
Frechet, Majoral, and others. These historical contributions have been reviewed
recently [52] .
This article will overview the dendritic architectural state, its unique architecturally driven properties, its role relative to traditional polymer science, and
describe the many enabling features that dendrimers are expected to offer to the
emerging nanotechnology revolution.
Twenty-First Century Polymer Science After Staudinger: The Emergence of. . .
333