Content area
Full Text
The interaction of polymers with their environment depends largely on the functional groups they carry. Interfaces between different polymers or between polymers and other surfaces can be strengthened through the design of molecular interactions such as hydrogen bonding and through the control of polymer architecture. The placement of functional groups at polymer chain ends or in well-defined segments can determine the unimate properties. Three-dimensional synthetic polymers such as dendrimers can be fashioned to encapsulate reactive sites or provide highly controlled surfaces and interfaces.
The term "functional polymer" is used to describe polymers that carry reactive functional groups that can participate in chemical processes without degradation of the original polymer chains. Although functional polymers are abundant in nature, this article focuses exclusively on synthetic functional polymers that are obtained by covalent polymerization of simple monomers. Given the nature of the processes used in covalent polmerizations, the reactive groups of functional polymers may be incorporated into the main chain, as pendant groups, or even as the chain ends of the macromolecule (1). Examples of functional polymers with reactive groups in the main chain or in the side chain are poly(isoprene) (natural rubber) and poly(acrylamide), polymers that have carbon-carbon double bonds or primary amide functional groups at regular intervals throughout their main chain or pendant to the main chain, respectively.
FUNCTIONAL POLYMERS: FROM HOMOPOLYMERS TO BLOCK COPOLYMERS
Although both poly(isoprene) and poly(acrylamide) are vinyl homopolymers containing a single type of monomer unit throughout the polymer chain, functional polymers frequently incorporate two or more different monomers A and B scattered randomly throughout the chain (a random copolymer) or distributed within the chain in a more ordered fashion. Indeed, copolymers in which two vinyl monomers A and B are connected to one another in a regularly alternating fashion throughout the chain do exist (1), but these highly regular copolymers are seldom encountered. However, polymer chemistry provides useful techniques for the preparation of precisely structured block copolymers (2).
An AB diblock copolymer is characterized by polymer chains that each contain a sequence (block) of monomer A linked to a sequence of the second monomer B. In similar fashion, an ABA triblock would have a sequence of monomer A followed by a central sequence of B, itself attached to another sequence of...