Complex Polymer Systems
The past decade, in addition to developing a number of new synthetic capabilities, has produced a greater understanding concerning the manipulation of secondary interactions, and their potential role in the assembly of macromolecules. Furthermore, as these interactions have become better understood, it has become possible to utilize them in the generation of more complex polymer systems which can be used to create materials with highly controlled shape, function, and molecular arrangement. These novel macromolecular materials have been utilized to form unique organic-inorganic assemblies with controlled structure, materials systems that are responsive to the environment or external stimuli, and polymer networks with defined function and control.
Block copolymers represent perhaps the first examples of more complex macromolecular systems. Progression from the fundamental understanding of block copolymer morphology that was the focus of the field ten years ago has now led to observations concerning how to ultimately control these nanoscale assemblies. More recent studies have included the incorporation and preferential segregation of functional inorganic nanoparticles into different domains of more traditional di- and triblock copolymer morphologies, thus leading to new approaches for photonic, electro-optic and other active structures. Since the early observations of polymer micelles and vesicles (“polymersomes”) in solution, investigations of polymers with two or more different segments has been used to develop a range of nanostructures, from unique core-shell nanoparticles to nanoscale rods and 3D colloidal networks. Multicompartmental micelles have been generated by translating the novel structures achieved with ABC triblock copolymer systems to the world of solution assembly and organization.
One of the most rapidly growing areas in polymeric materials systems is the use of electrostatic interactions between polyelectrolytes to construct nanocomposite thin films via the layer-by-layer technique. This technique, first introduced in 1989, has expanded rapidly over the past decade as a means of creating a range of hybrid materials systems. The ability to control the film composition on the nanometer length scale enables the incorporation of a range of polymeric materials with highly different compositions, thus enabling polymer “blends” between two polymer backbones that would not ordinarily form a stable blend. Because these films are extremely conformal, they can be templated onto a range of micro- to nanoscale surfaces, isolated, and further manipulated to generate functional nanostructures, including magnetically responsive nanotubes, controlled drug release films, and electrochemical systems.
The construction of oligomeric or polymer species that assemble to create larger supramolecular systems has led to unique responsive gels and networks. The clever choice of biocompatible polymer systems such as polypeptides or poly(ethylene oxide) have led to materials systems with precise control and placement of functional systems, including the design of 2D surfaces for the control of biomaterials surfaces, and 3D scaffolds for cellular systems. Many of these topics get their inspiration from biological systems.