Macromolecular gels

Cross-linked macromolecular gels have been prepared by Eriedel-Crafts cross-linking of polystyrene with a dihaloaromatic compound, or Eriedel-Crafts cross-linking of styrene—chloroalkyl styrene copolymers. These polymers in their sulfonated form have found use as thermal stabilizers, especially for use in drilling fluids (193). Cross-linking polymers with good heat resistance were also prepared by Eriedel-Crafts reaction of diacid haUdes with haloaryl ethers (194). 

Nakao, S-I Nomura, T Kumura, S, Characteristics of Macromolecular Gel Layer Formed on Ultrafiltration Tubular Membrane, AIChE Journal 25, 615, 1979. 

Birr 156) finds that the reactions on supports like 1 % cross-linked polystyrene in suitable solvents are not strictly solid-phase reactions, even if the particles look solid. Under these loosely cross-linked conditions, the polymer exists in a quasi-dissolved gel state, and the reactivity of the chain molecule is not considerably reduced in any way by the gel character. The free motion of the large chain segments in the swollen state of the macromolecular gel phase — which is only very lightly cross-linked just to give macroscopic insolubility — guarantees reactivity which is not much different from the corresponding linear, soluble macromolecule. 

Macromolecular Gel permeation Molecular weight Viscosity, toughness... 

Feuillade, G., Perche, E, 1975. Ion-conductive macromolecular gels and membranes for solid lithium cells. J. Appl. Electrochem. 5,63-69. 

On the molecular level, coal is an extremely complex substance and in spite of extensive research in this area the exact structure of coal has yet to be determined (Chapter 10). Different authors have proposed various coal models from time to time. Broadly it is agreed that coal consists of heterogeneous polyaromatic clusters in a complex array resulting in a highly cross-linked macromolecular gel structure. Another opinion that coal has a highly associated structure also exists. 

These colloidal systems, see definition in 1 b (p. 2), exist both in macromolecular and association colloids. Here only the most important types of macromolecular gels will be considered. For their realisation it seems essential for the macromolecules in question to be of the randomly kinked lor chain type (see Ch. XII, p. 483),... 

One-phase macromolecular gels, representing solid solutions of solvent and macromolecular substance. 

Though this volume treats the macromolecular aspects of colloid science and though we shall, hence, mainly focus attention on macromolecular gels in this chapter, it seemed necessary to include also a discussion of gels in general, since this subject has not yet been treated elsewhere in this book, and, for more than one reason a separate treatment seemed to be undesirable. 

According to modern views, the gels formed from solutions of linear macromolecules may in many instances also be considered as due to a process of crystallisation or at least to something very similar to crystallisation For obvious reasons a recrystallisation to form larger microscopically visible individual crystals does, however, not occur in macromolecular gels ... 

A particular example of a macromolecular gel is the silicic acid gel, which is formed from sodium silicate solutions upon acidification. According to WiLLSTaxTER et aL mono or disilicic acids are formed in the reaction, which undergo polymerisation giving rise to high molecular silicic adds Since the polymerisation is a 3-dimensional one, a molecular framework is built. Polymerisation continues long after the solution has set to a gel. The case is comparable to that of the polymerisation of phenolformalde-hyde solutions setting to a gel (cf. Ch. II, p. 39). 

Though this classical interpretation may still be preferable in certain cases, it has recently been recognised that in the typical macromolecular gels sorption should be regarded as a homogeneous dissolution of the sorbate in the sorbent quite comparable to the absorption of e. g., carbon bisulphide vapour by paraffin oil or the absorption of water in sulphuric acid. 

Syneresis is very common in gels. It is met with in macromolecular gels with water as well as in those with organic liquids as a solvent (e. g. rubber gels ). It is not confined to macromolecular systems but also occurs in gels formed from crystalli able substances, in the gels of the heavy metal hydroxides and the like... 

Chemical reactions in swollen gels whereby the macromolecular gel component is chemically changed will, of course, be of a topochemical character. The rate of the reaction will not only depend on the velocity coefficient of the reaction itself, but also on diffusion processes. The reagent has to diffuse into the gel to reach the scene of the reaction and reaction products will eventually have to leave that place by diffusion. Patches of the gel near its surface may react sooner than those farther away from the surface, if the reaction velocity is not very much smaller than the rate of diffusion. 

In the steric exclusion mechanism, the gel is assumed to act as an inert matrix holding the solvent in its pores. However, it seems likely that the properties of the solvent in gel differ from those of bulk of the solvent by the possible interaction between the solvent molecule and the gel matrix. For instance, water molecules in macromolecular gels generally exhibit physical properties distinct from those of ordinary free water by the interaction with hydrophilic groups or hydrophobic part of the gel matrix [ref. 58-61]. Heitz [ref. 

In addition to small molecular gels, the covalent capture or cross-linking of macromolecular gels has also... 

Aizawa, M. and Suzuki, S, Properties of water in macromolecular gels. III. Dilatometric studies of the properties of water in macromolecular gels. Bull. Chem. Soc. Jpn. 44(11) 2967 (1971). 

DILLON R A and SHRivER D F (2001), lon transport and vibrational spectra of branched polymer and dendrimer electrolytes , Chem Mater, 13 1369-1373 FENTON D E, PARK J M and WRIGHT p V (1973), Complexes of alkali metal ions with poly (ethylene oxide) . Polymer, 14 589-589 FEUILLADE G and PERCHE p (1975), lon-condnctivc macromolecular gels and membrane for solid lithium cells , J Appl Electrochem, 5 63-69 FONTENELLA J J, WINTERGILL M C, CALAME J P and ANDEEN C G (1983), Electrical relaxation in pure and alkah metal thiocyanate complexed poly(ethylene oxide) . Solid State Ionics, 8 333—339... 

---