15
Nanostructured Polymers
S. Ramakrishnan
Abstract
During the latter half of the 20th century, polymer chemists have successfully developed the necessary tools to control various molecular structural parameters
in synthetic macromolecules, such as their molecular weight and polydispersity,
regio- and stereo-regularity, topology of repeat unit connectivity, such as in the case
of dendrimers, and to a limited extent even copolymer sequence distribution.
However, the control over the next level of organization, namely chain conformation and the subsequent packing of chains in the macroscopic dimension, has
proven to be a far more difficult task. Control of molecular organization in the
nanometer dimensions and subsequent organization of these nanoscale entities
could be one way to define nanostructured polymers. An alternative way to perceive this class of materials would be to disregard molecular-level structural order
present in the sub-nanometer dimension and focus only on the generation of wellcontrolled nanometer-size polymeric objects, such as nanospheres, nanocapsules,
nanofibres, nanotubes, etc. In this chapter I shall deal with both these aspects
separately, and highlight, using recent examples, the various approaches that have
been used to achieve this objective.
15.1
Introduction
Efforts at controlling molecular ordering at smaller and smaller dimensions are
driven, on the one hand, by the immense potential technological implications and,
on the other, by the desire to emulate the sheer beauty and elegance with which
nature is able to control hierarchical structural organization, which spans over very
wide length scales. Nanostructural control in synthetic polymeric systems implies
the control of structure and dimension in the 1–100 nm size domain, although
slightly larger sizes, up to several microns, have also often been included within
this category. In synthetic polymeric systems, control of nanostructure has been
achieved via two distinct approaches: one using block copolymers and the other
476
Nanostructured Polymers
S. Ramakrishnan
Abstract
During the latter half of the 20th century, polymer chemists have successfully developed the necessary tools to control various molecular structural parameters
in synthetic macromolecules, such as their molecular weight and polydispersity,
regio- and stereo-regularity, topology of repeat unit connectivity, such as in the case
of dendrimers, and to a limited extent even copolymer sequence distribution.
However, the control over the next level of organization, namely chain conformation and the subsequent packing of chains in the macroscopic dimension, has
proven to be a far more difficult task. Control of molecular organization in the
nanometer dimensions and subsequent organization of these nanoscale entities
could be one way to define nanostructured polymers. An alternative way to perceive this class of materials would be to disregard molecular-level structural order
present in the sub-nanometer dimension and focus only on the generation of wellcontrolled nanometer-size polymeric objects, such as nanospheres, nanocapsules,
nanofibres, nanotubes, etc. In this chapter I shall deal with both these aspects
separately, and highlight, using recent examples, the various approaches that have
been used to achieve this objective.
15.1
Introduction
Efforts at controlling molecular ordering at smaller and smaller dimensions are
driven, on the one hand, by the immense potential technological implications and,
on the other, by the desire to emulate the sheer beauty and elegance with which
nature is able to control hierarchical structural organization, which spans over very
wide length scales. Nanostructural control in synthetic polymeric systems implies
the control of structure and dimension in the 1–100 nm size domain, although
slightly larger sizes, up to several microns, have also often been included within
this category. In synthetic polymeric systems, control of nanostructure has been
achieved via two distinct approaches: one using block copolymers and the other
476