The term "alloy" as pertaining to polymers has become an increasingly popular description of composites of polymers, parti cularly since the publication of the first volume in this series in 1977. Polymer alloy refers to that class of macromolecular materials which, in general, consists of combinations of chemically different polymers. The polymers involved in these combinations may be hetero geneous (multiphase) or homogeneous (single phase). They may be linked together with covalent bonds between the component polymers (block copolymers, graft copolymers), linked topologically with no covalent bonds (interpenetrating polymer networks), or not linked at all except physically (polyblends). In addition, they may be linear (thermoplastic), crosslinked (thermosetting), crystalline, or amorphous, although the latter is more common. To the immense satisfaction - but not surprise - of the editors, there has been no decrease in the research and development of polymer alloys since the publication of the first volume, as evidenced by numerous publications, conferences and symposia. Continued advances in polymer technology caused by the design of new types of polymer alloys have also been noted. This technolog ical interest stems from the fact that these materials very often exhibit a synergism in properties achievable only by the formation of polymer alloys. The classic examples, of course, are the high impact plastics, which are either polyblends, block, or graft co polymers composed of a rubbery and a glassy polymer. Interpene trating polymer networks (IPN's) of such polymers also exhibit the same, or even greater, synergism.

Distinguishing among blends, alloys and other types of combinations, clarifying terminology and presenting data on new processes and materials, this work present up-to-date and effective compounding techniques for polymers. It offers extensive analyses on the challenging questions that surround miscibility, compatibility, dynamic processing, interaction/phase behaviour, and computer simulations for predicting behaviours of polymer mixture and interaction.

P. S. HOPE and M. J. FOLKES Mixing two or more polymers together to produce blends or alloys is a well-established strategy for achieving a specified portfolio of physical proper ties, without the need to synthesise specialised polymer systems. The subject is vast and has been the focus of much work, both theoretical and experimental. Much ofthe earlier work in this field was necessarily empirical and many ofthe blends produced were of academic rather than commercial interest. The manner in which two (or more) polymers are compounded together is of vital importance in controlling the properties of blends. Moreover, particular ly through detailed rheological studies, it is becoming apparent that process ing can provide a wide range of blend microstructures. In an extreme, this is exemplified by the in situ formation of fibres resulting from the imposition of predetermined flow fields on blends, when in the solution or melt state. The microstructures produced in this case transform the blend into a true fibre composite; this parallels earlier work on the deformation of metal alloys. This type of processing-structure-property correlation opens up many new possi bilities for innovative applications; for example, the production of stiff fibre composites and blends having anisotropic transport properties, such as novel membranes. This book serves a dual purpose.

An introduction to polymer alloys and blends.

Alloy is a term commonly associated with metals and implies a composite which may be sinqle phase (solid solution) or heterophase. Whichever the case, metallic alloys generally exist because they exhibit improved properties over the base metal. There are numer ous types of metallic alloys, including interstitial solid solutions, substitutional solid solutions, and multiphase combinations of these with intermetallic compounds, valency compounds, electron compounds, etc. A similar situation exists with polymers. There are numerous types of composites, or "alloys" of polymers in existence today with new ones being created continuously. Polyblends are simple physical mixtures of the constituent polymers with no covalent bonds occuring between them. As with metals, these may be homogeneous (single phase) solid solytions or heterogeneous (multiple phase) mixtures. With polymers, the latter case is by far the most prevalent situation due to the thermodynamic incompatibility of most polymers. This is due to the relatively small gain in entropy upon mixing the polymers due to contiguity restrictions imposed by their large chain length.

Polymer Blends, Volume 2 aims to show the importance of mixed polymer systems as a major branch of macromolecular science and provides a broad background of principles and practices in this field. Starting from where the first volume left off, the book covers topics in the area of polymer blends in Chapters 11-23. Areas of coverage include interpenetrating polymer networks; interfacial agents for polymer blends; rubber modification of plastics; fracture phenomena; coextruded multilayer polymer films and sheets; polymeric plasticizers; and polyolefin blends and their applications. The book is recommended for scientists, technologists, and engineers in the academe, research, and related industry, especially those who wish to be updated with its advances as a science.