POLYMER LElTERS EDITION 5 85

developments of polyurethanes for reaction injection molding and (glass fiber) reinforced reaction injection molding (Allport, Barker, Chapman). A not too extensive Subject Index concludes the volume.

Edited books often suffer from uneven treatment; however, in this volume efforts have been made to balance the presentations and the different viewpoints of specifics (e.g., polyurethanes) complement each other.

In summary, this volume is highly recommended to materials scientists who want to keep pace with the synthesis-physical chemistry-morphology and to a lesser extent physical properties of block copolymers.

Joseph P. Kennedy

Institute of Polymer Science University of Akron Akron, Ohio 44325

Twin-Screw Extruders - A Basic Understanding, Fabrizio Martelli, Van Nostrand Reinhold, New York, 1982, 137 pp. Price: $32.50.

This book is aimed ostensibly at conveying some basic concepts of twin-screw extruders. Realizing the complexity involved in discussing the subject matter, I can understand the reason(s) why the author has taken such a very naive and primitive approach to describing the subject. On the other hand, there is no ex- cuse for someone to write a monograph if one cannot (or does not wish to) dis- cuss the truly basic concepts and principles involved with the physical system to be dealt with. Frankly, I find little of value in the book, from the points of view of a teacher and researcher.

No fundamental equations are derived on the basis of first principles describ- ing the motion of materials in a twin-screw extruder, either counterrotating or corotating. The performance of twin-screw extruders depends on among many factors, the design of the screws, which is, after all, responsible for mixing. As a matter of fact, the industry chooses this expensive machine (expensive compared with single-screw extruders), because the twin-screw machine gives a better mix- ing than the single-screw machine. Therefore, the reader would expect to find, in a book like this, the reasons for the choice of the twin-screw machine. Rea- sons must be given in a believable fashion, either theoretical or semiempirical. I could not find any such information in this book.

There are three major roles for twin-screw extruders in polymer process in- dustry. One is to prepare compounds by mixing various polymers for preparing blends, or mixing fillers and polymers for preparing polymer composites, or mix- ing special ingredients and polymers for preparing specific compounds. Another role is as a substitute for a polymerization reactor. Still another role is to re-

5 86 POLYMER LETTERS EDITION

move residual monomer or solvent from polymerization reactor products, a pro- cedure often referred to as polymer devolatilization.

I hope that someday a book will be available that discuses these various as- pects of twin-screw extruder operation, from the points of view of the polymer fabricator and the machine designer.

C. D. Han

Department of Chemical Engineering Polytechnic Institute of New York Brooklyn, New York 11201

Electronic Properties of Polymers, J . Mort and G. Pfister, Eds., Wiley, New Yo&, 1982,336 pp. Price: $39.00.

This book consists of a collection of six articles on various aspects of the elec- tronic structure of polymers as well as charge and energy transport therein. A survey of the electronic properties of various classes of polymers is given in the opening chapter by J. J. Ritsko who also indicates the relationship between the bulk electronic structure and triboelectric contact charge exchange. Charge transport, photogeneration, and photosensitization are considered in an article written by the editors. Energy transfer is reviewed in the chapter by W. Klopffer. TWO further chapters on charge storage by G. M. Sessler and on piezoelectricity and pyroelectricity by Y. Wada deal with special topics pertaining to applications of polymers as electrets and transducers, respectively. An article on conducting polymers by D. Baeriswyl, G. Harbeke, H. Kiess, and W. Meyer constitutes the concluding chapter in the book.

The editors’ articulated objective is to acquaint a broader audience of mate- rials scientists generally and polymer scientists more particularly with “an up-to- date assessment of our understanding of the electronic properties of polymers and their actual or potential technological applications.” “Acquaint” is definite- ly the proper term. The separate chapters vary widely in both readability and the comprehensiveness with which the Literature is reviewed. The editors indicate that “the chapters are not intended to be allembracing reviews of the field.” In- deed, they are not. According to the editors these chapters are, however, intend- ed “to present a detailed discussion of key ideas and directions with the objec- tive of delineating the most pressing and exciting problems.” Two chapters, those by Ritsko and by Baeriswyl, Harbeke, Kiess, and Meyer come close to achieving this objective. The others tend to deal with material that has been reviewed fairly widely elsewhere. Almost all of the authors present their topics with a rather personal flavor, so that a balanced view of the literature is not found in this volume.