This book contains a number of articles inspired by the NATO Advanced Study Institute on 'Charged and Reactive Polymers l' held in France in June 1972. This general title indicates simply the intention of a series. The meeting dealt mainly with the fundamental problems of the physical chemistry of polyelectrolytes in solution. Some of the articles reproduce the lectures exactly as they were delivered. Some others have been modified to a greater or lesser extent, and this as a result of improvements or new inspiration arising from comments and discussions. In previous larger conferences on macromolecules, polyelectrolytes constituted only a marginal problem and few were the individual communications or short was the time al10tted to this subject. In other meetings of a biophysical character the uses of the techniques of charged macromolecules have been exposed with less attention given to the theories or to the creation or interpretation of these techniques. AU of us felt that the time had come to enumerate and to evaluate this increasing science of polyelectrolytes which has become of major interest. During the whole period of the Institute physical chemists discussed their mutual problems for more than a week, and of ten far into the night One of the advantages of such an Institute is to enable the Directors and the mem bers of the Scientific Committee to establish a logical order in the lectures; this order has been respected in the present edition."

The first four volumes of the series on 'Charged and Reactive Polymers' have been devoted to polymers in solution (Voh. I and II) or in gel and membrane forms (Vols. III and IV). In correlation with charges, other physical or chemical properties of macro molecules have been considered. Understanding of charge and hydrophobic effects is equally important for synthetic and biopolymers or their systems. Optically Active Polymers are related to problems of the same class, since optical activity is an inherent property of both natural macromolecules as well as a great variety of polymers synthesized in the Jast twenty years. Optical activity is a physical spectral property of chiral matter caused by asymmetrical configurations, conformations and structures which have no plane and no center of symmetry and consequently have two mirror image enantiomeric forms of inverse optical rotation. The racemic mixture of chiral enantiomers is optically inactive. The most common form of optical activity was first measured at a constant wavelength by the angle of rotation of linearly polarized light. More recently the measurements have been extended to the entire range of visible and attainable ultraviolet regions where electronic transitions are observed, giving rise to the ORD technique (Optical Rotatory Dispersion). The Cotton effects appear in the region of optically active absorption bands; outside of these bands the plain curve spectrum is also dependent on all the electronic transitions of the chromophores."

Polyelectrolytes and their Applications is the second volume in the series 'Charged and Reactive Polymers'. The important areas of polyelectrolyte applications, i.e., biomedicine, water purification, petroleum recovery and drag reduction, are pre sented along with discussions of the fundamental principles of polyelectrolyte chem istry and physics. This book should be of interest to scientists such as physicians, biochemists, polymer chemists and chemical engineers involved in applications of these materials. The first part of the book is devoted to the basic properties of polyelectrolytes in general, namely to the factors influencing the chain conformation of charged polymers in solution and to their counterion selectivity. It also contains methods of synthesis and new concepts of charge stabilized polymer colloids and of polyelectrolyte ca talysis. The second part describes recent information on the properties and biological effects of already well-known natural polyelectrolytes such as heparin and DNA and recently developed polymers such as pyran and polyionenes. The effects of poly anions and polycations on normal and transformed cells as well as on acetylcholine receptors follow. This part is of particular interest to scientists involved in biological research."

The introduction to the first of these two volumes on Charged Gels and Membranes has recalled already that both were issued from the second Advanced Study Institute of Forges les Eaux, of which the co-directors were Professors G. E. Boyd and K. S. Spiegler. However, it seems necessary to add some further remarks for the eventual readers of this one volume only or for those of all four which now constitute the series. * One discovers that each volume is precisely linked to the next; and the total con tains a large number of the very fundamental steps by which macromolecular physical chemistry finds itself simultaneously at thefronNers of application and of biology. One often wonders how this is possible. Research has been the best means of unders anding the microscopic elements oflife. Biomimetic phenomena or bioanalogue compounds in their turn have led to innumerable practical realisations. On one hand, the notion of 'vital force' receded and is disap pearing due to repetitive total and asymmetric synthesis* of always larger, and more complex, biological molecules. On the other hand discoveries of inter-relations in physical chemistry disengage the analogies between living and non-living systems: the interrelations between phenomena, between phenomena and structures or the appear ance of these structures under the influence of intermolecular forces or of gradients of more statistical forces."

This book contains a number of articles inspired by the NATO Advanced Study Institute on 'Charged and Reactive Polymers l' held in France in June 1972. This general title indicates simply the intention of a series. The meeting dealt mainly with the fundamental problems of the physical chemistry of polyelectrolytes in solution. Some of the articles reproduce the lectures exactly as they were delivered. Some others have been modified to a greater or lesser extent, and this as a result of improvements or new inspiration arising from comments and discussions. In previous larger conferences on macromolecules, polyelectrolytes constituted only a marginal problem and few were the individual communications or short was the time al10tted to this subject. In other meetings of a biophysical character the uses of the techniques of charged macromolecules have been exposed with less attention given to the theories or to the creation or interpretation of these techniques. AU of us felt that the time had come to enumerate and to evaluate this increasing science of polyelectrolytes which has become of major interest. During the whole period of the Institute physical chemists discussed their mutual problems for more than a week, and of ten far into the night One of the advantages of such an Institute is to enable the Directors and the mem bers of the Scientific Committee to establish a logical order in the lectures; this order has been respected in the present edition."

The first four volumes of the series on 'Charged and Reactive Polymers' have been devoted to polymers in solution (Voh. I and II) or in gel and membrane forms (Vols. III and IV). In correlation with charges, other physical or chemical properties of macro molecules have been considered. Understanding of charge and hydrophobic effects is equally important for synthetic and biopolymers or their systems. Optically Active Polymers are related to problems of the same class, since optical activity is an inherent property of both natural macromolecules as well as a great variety of polymers synthesized in the Jast twenty years. Optical activity is a physical spectral property of chiral matter caused by asymmetrical configurations, conformations and structures which have no plane and no center of symmetry and consequently have two mirror image enantiomeric forms of inverse optical rotation. The racemic mixture of chiral enantiomers is optically inactive. The most common form of optical activity was first measured at a constant wavelength by the angle of rotation of linearly polarized light. More recently the measurements have been extended to the entire range of visible and attainable ultraviolet regions where electronic transitions are observed, giving rise to the ORD technique (Optical Rotatory Dispersion). The Cotton effects appear in the region of optically active absorption bands; outside of these bands the plain curve spectrum is also dependent on all the electronic transitions of the chromophores."

The series on 'Charged and Reactive Polymers' was set forth in two volumes concern ing the fundamentals and applications of polyelectrolytes. A follow-up on 'Charged Gels and Membranes' would therefore seem appropriate, necessitating, however, some explanation for non-specialists. Theories of the most dilute gels originate in that of concentrated polyelectrolytes: the methods and problems are similar in structural, spectroscopic or thermodynamic properties. The borderline can be situated in dialysis conducted with a 'bag' imper meable to polyelectrolytes but not to small ions, solutes and water. One may recall Donnan's use of such a system to experiment and discover his famous law of unequal distribution of ions of different charge inside and out. Remark ably so, it is the difference in scale which characterizes the difference between poly electrolyte solutions and gels and membranes: the colloidal solution of macro molecules is heterogeneous only on the microscopic level, whereas the gel-solution system is a macroscopically heterogeneous one. A gel is formed when weak or strong cohesive forces counterbalance the dispersing ones (usually by crosslinking) without inhibiting the penetration of solvent and of small solutes into the polymeric network. The solvophile macromolecules cannot invade the total volume of liquid. As a result of phase-segregation excess solution and gel coexist and interact. The macroscopic swelling depends on gel cross-linking as well as on ionic concentration and type and ion-selectivities are observed."