1 Introduction
Commemorating the 60th anniversary of the Nobel Prize being awarded to
Hermann Staudinger for his pioneering studies to establish the field of organic
polymer chemistry [1, 2] gives us an opportunity to reflect upon the hierarchical
structures that are achievable in macromolecules and supramolecular polymers. In
1953, the idea that natural and synthetic sources could be used to prepare organic
molecules composed of tens of thousands if not millions of atoms had solidified
[2]. At the same time, details of the solid state structures of polypeptides [3–6], poly
(nucleic acid)s [7], and polyolefins [8] were only beginning to emerge and reveal
perfectly repeating conformations in monomer units that yield helical structures.
Molecular design and chemical synthesis strategies to control the handedness of
helical polymers have since been established [9–12], opening opportunities for
creating materials whose functional properties relate to the organization of helical
building blocks [13–15]. Understanding the hierarchy through which information in
molecular building blocks is expressed as macroscopic properties and functions
is essential if we are to take full advantage of macromolecular materials and
supramolecular polymers.
Macromolecules that contain two or more topologically distinct components are
complex architectures that can lead to emergent properties or behaviors that are
different to those of either of the individual molecular architectures. Dendronized
polymers [16–19] are examples of such complex molecular architectures and are
composed of a linear polymer backbone and perfectly branched dendritic side
chains on each repeat unit (Scheme 1). The molar masses of such polymers
emphasize the shift in thinking brought about by Staudinger’s concept of macromolecules [1, 2]. Individual dendronized polymers are nanoscopic objects [20–25]
whose organization in bulk is determined by hierarchical processes that occur on a
different set of length scales compared to conventional polymers [16, 26]. By virtue
of the size and shape of dendronized polymers, interest in this complex macromolecular architecture has moved toward how to extract functionality from these
nanoscale molecular objects.
Dendronized polymers that have a helical polymer backbone are of special
interest for understanding the structure of dendronized polymers as well as the
hierarchy of self-assembly and self-organization events that occur upon going from
dilute solution to bulk material. Because of the large volume occupied by the
dendritic side chains (Scheme 1), the conformational degrees of freedom available
to a flexible polymer backbone are reduced [21, 27–34] and it is possible to obtain
helical dendronized polymers from a wide range of polymer backbones. Comparison of the structures of dendronized helical polymers with the structures of
dendronized polymers with more flexible backbones have confirmed that flexible
polymer backbones adopt a helical conformation upon encapsulation within a
dendritic sheath [35, 36]. Efforts to program the handedness of helical dendronized
polymers [35–42] have helped answer fundamental questions on how
homochirality emerged in biological systems [43–45], and these polymers can be
346
J.G. Rudick
Commemorating the 60th anniversary of the Nobel Prize being awarded to
Hermann Staudinger for his pioneering studies to establish the field of organic
polymer chemistry [1, 2] gives us an opportunity to reflect upon the hierarchical
structures that are achievable in macromolecules and supramolecular polymers. In
1953, the idea that natural and synthetic sources could be used to prepare organic
molecules composed of tens of thousands if not millions of atoms had solidified
[2]. At the same time, details of the solid state structures of polypeptides [3–6], poly
(nucleic acid)s [7], and polyolefins [8] were only beginning to emerge and reveal
perfectly repeating conformations in monomer units that yield helical structures.
Molecular design and chemical synthesis strategies to control the handedness of
helical polymers have since been established [9–12], opening opportunities for
creating materials whose functional properties relate to the organization of helical
building blocks [13–15]. Understanding the hierarchy through which information in
molecular building blocks is expressed as macroscopic properties and functions
is essential if we are to take full advantage of macromolecular materials and
supramolecular polymers.
Macromolecules that contain two or more topologically distinct components are
complex architectures that can lead to emergent properties or behaviors that are
different to those of either of the individual molecular architectures. Dendronized
polymers [16–19] are examples of such complex molecular architectures and are
composed of a linear polymer backbone and perfectly branched dendritic side
chains on each repeat unit (Scheme 1). The molar masses of such polymers
emphasize the shift in thinking brought about by Staudinger’s concept of macromolecules [1, 2]. Individual dendronized polymers are nanoscopic objects [20–25]
whose organization in bulk is determined by hierarchical processes that occur on a
different set of length scales compared to conventional polymers [16, 26]. By virtue
of the size and shape of dendronized polymers, interest in this complex macromolecular architecture has moved toward how to extract functionality from these
nanoscale molecular objects.
Dendronized polymers that have a helical polymer backbone are of special
interest for understanding the structure of dendronized polymers as well as the
hierarchy of self-assembly and self-organization events that occur upon going from
dilute solution to bulk material. Because of the large volume occupied by the
dendritic side chains (Scheme 1), the conformational degrees of freedom available
to a flexible polymer backbone are reduced [21, 27–34] and it is possible to obtain
helical dendronized polymers from a wide range of polymer backbones. Comparison of the structures of dendronized helical polymers with the structures of
dendronized polymers with more flexible backbones have confirmed that flexible
polymer backbones adopt a helical conformation upon encapsulation within a
dendritic sheath [35, 36]. Efforts to program the handedness of helical dendronized
polymers [35–42] have helped answer fundamental questions on how
homochirality emerged in biological systems [43–45], and these polymers can be
346
J.G. Rudick