Gradient polymers and copolymers

Abstract

Gradient polymers are two component polymeric systems in which the concentration of one component varies in a continuous way from one side to the other in systems with plane-parallel geometry. Such systems can be obtained from an amorphous polymeric matrix by diffusing into another monomer creating a gradient of concentration, which is fixed by, for example, photo-polymerization. Properties of such systems with plane-parallel geometry are discussed. Paricular attention is given to the systems with cylindrical geometry in which the gradient of the second polymer varies from the center to outside. This class of gradient polymers has a great practical application as gradient optical polymeric fibers and multifocal lenses. An interesting and new class of gradient polymers are systems systems consisting of semicrystalline polymeric matrices in which a gradient of structure is created by appropriate thermal treatment and an amorphous polymer gradient is formed by diffusion of a monomer and its subsequent polymerization. The structural, thermal and mechanical properties are discussed mainly for a model system consisting of polyethylene and polystyrene. The polymeric gradient systems, consisting of an oriented semicrystalline polymer and amorphous gradient polymer, are discussed showing that the structurally gradient matrices and amorphous polymer offer a great variety of factors which can influence the properties of multicomponent gradient polymers. Recently obtained gradient copolymers in which the chemical composition varies from one end to the other a macromolecule are presented. It is shown how such macromolecules can be obtained with different type of changes of the composition. The unusual properties of gradient copolymers are discussed considering their mechanical and thermal properties as well their specific behaviour as compatibilizers. © 1998 John Wiley & Sons, Ltd.