BACKGROUND Polysiloxanes have chains constructed of alternately arranged silicon and oxygen atoms with organic groups attached to the silicon atoms. This structure gives them a unique combination of properties that hold great interest for a host of practical applications. Although they have been known and manufactured for many years, their applications continue to expand rapidly and this boosts progress in the generation of new and modified polysiloxanes. Polysiloxanes constitute the oldf'"' known class of silicon-based polymers and the broadest one when viewed in terms of the variety of structures differing in topology and the constitution of organic substituents. There are also many and various types of siloxane copolymers, some of purely siloxane structure and others of siloxane-organic composition. There is no doubt that polysiloxanes are the most technologically important silicon-based polymers. The broad class of model materials known as silicones is based on polysiloxanes. They are also the best known, as most research in the area of silicon polymers has for many years been directed towards the synthesis of new polysiloxanes, to understanding their properties and to extending their applications.

Nuclear magnetic resonance spectroscopy, which has evolved only within the last 20 years, has become one of the very important tools in chemistry and physics. The literature on its theory and application has grown immensely and a comprehensive and adequate treatment of all branches by one author, or even by several, becomes increasingly difficult. This series is planned to present articles written by experts working in various fields of nuclear magnetic resonance spectroscopy, and will contain review articles as well as progress reports and original work, its main aim, however, is to fill a gap, existing in literature, by publishing articles written by specialists, which take the reader from the introductory stage to the latest development in the field. The editors are grateful to the authors for the time and effort spent in writing the articles, and for their invaluable cooperation. The Editors Contents P. Diehl and C. L. Khetrapal NMR Studies of Molecules Oriented in the Nematic Phase of Liquid Crystais......................................................... 1 R. G. Jones The Use of Symmetry in Nuclear Magnetic Resonance................. 97 NMR Studies of Molecules Oriented in the Nematic Phase of Liquid Crystals P. DIEHL and C. L. KHETRAPAL * Department of Physics, University of Basel, Switzerland Contents 1. Introduction . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Liquid Crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 . . . . . . . . . . . . . . 2.1. Classification of Liquid Crystal Phases . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Theories of the Liquid Crystalline State . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Nematic Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1 4. Basic Theory (for I = I ). . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . . . . . . . 7 . .

BACKGROUND Polysiloxanes have chains constructed of alternately arranged silicon and oxygen atoms with organic groups attached to the silicon atoms. This structure gives them a unique combination of properties that hold great interest for a host of practical applications. Although they have been known and manufactured for many years, their applications continue to expand rapidly and this boosts progress in the generation of new and modified polysiloxanes. Polysiloxanes constitute the oldf'"' known class of silicon-based polymers and the broadest one when viewed in terms of the variety of structures differing in topology and the constitution of organic substituents. There are also many and various types of siloxane copolymers, some of purely siloxane structure and others of siloxane-organic composition. There is no doubt that polysiloxanes are the most technologically important silicon-based polymers. The broad class of model materials known as silicones is based on polysiloxanes. They are also the best known, as most research in the area of silicon polymers has for many years been directed towards the synthesis of new polysiloxanes, to understanding their properties and to extending their applications.

This is a reproduction of a book published before 1923. This book may have occasional imperfections such as missing or blurred pages, poor pictures, errant marks, etc. that were either part of the original artifact, or were introduced by the scanning process. We believe this work is culturally important, and despite the imperfections, have elected to bring it back into print as part of our continuing commitment to the preservation of printed works worldwide. We appreciate your understanding of the imperfections in the preservation process, and hope you enjoy this valuable book. ++++ The below data was compiled from various identification fields in the bibliographic record of this title. This data is provided as an additional tool in helping to ensure edition identification: ++++ The Circus Reader Bertha Elinor Buffington, Theresa Weimer, R. G. Jones B. H. Sanborn & co., 1909 Language Arts & Disciplines; General; Language Arts & Disciplines / General; Readers