Copolymer-solvent systems

For polymers whose Mw < 10,000, the intensity of light scattering from the solution differs so little from the neat solvent that the determination is not precise. For polymers whose Mw > 10,000, the need to measure the light scattering at very small values of 0 is beyond the capability of many older instruments. Special treatment is required for mixed solvent systems, copolymers, higher polymers, and polyelectrolytes. 

Membrane stmcture is a function of the materials used (polymer composition, molecular weight distribution, solvent system, etc) and the mode of preparation (solution viscosity, evaporation time, humidity, etc). Commonly used polymers include cellulose acetates, polyamides, polysulfones, dynels (vinyl chloride-acrylonitrile copolymers) and poly(vinyhdene fluoride). 

Unlike earlier sulfonated styrene/divinylbenzene copolymers, these sulfonated gels can he run in virtually any solvent from water and buffers to pure organics as well as most any mixed solvent systems desired. In aqueous systems they absorb water and in organic solvents they stay swollen by imbibing organic solvents. 

The formation mechanism of structure of the crosslinked copolymer in the presence of solvents described on the basis of the Flory-Huggins theory of polymer solutions has been considered by Dusek [1,2]. In accordance with the proposed thermodynamic model [3], the main factors affecting phase separation in the course of heterophase crosslinking polymerization are the thermodynamic quality of the solvent determined by Huggins constant x for the polymer-solvent system and the quantity of the crosslinking agent introduced (polyvinyl comonomers). The theory makes it possible to determine the critical degree of copolymerization at which phase separation takes place. The study of this phenomenon is complex also because the comonomers act as diluents. 

Preparation of siloxane-carbonate segmented copolymers by interfacial polymerization involves the reaction of carboxypropyl-terminated siloxane oligomers with bisphenol-A and phosgene, in the presence of a strong base and a phase transfer catalyst, in water/methylene chloride solvent system l50 192), as shown in Reaction Scheme XIV. 

Using the random phase approximation (RPA), the coherent scattering intensity Icoh(Q, t) of a polymer blend/solvent or a diblock copolymer/solvent system can... 

C(Q) and Q Q) are the characteristic frequencies attributed to the cooperative and the interdiffusion modes, respectively. In the case of the copolymer solvent system, the interdiffusion mode originates from the relative motion of one block with respect to the other. 

In a more general way, the loading of metal salts into preformed block copolymer micelles has become the most used route for the incorporation of precursors into block copolymer nanostructures because it allows precursor loading with tolerable loading times, it is quite versatile, and it is applicable to a wide variety of precursor/block copolymer/solvent systems. The accordingly synthesized polymer-coated metallic or semiconducting nanoparticles exhibit increased stability, which results in, e.g., protection against oxidation as illustrated by Antonietti et al. [108]. 

It is clear, therefore, that polymers synthesized by polycondensation of sugars in acidic methyl sulfoxide are, actually, copolymers of sugars and formaldehyde in which some of the glycosyl residues are joined by glycosidic bonds, and others are linked by bridges of oxymethylene units. Nonetheless, because polycondensation of sugars can be effected in methyl sulfoxide, and because the methods developed for the polycondensation may be applicable to other solvent systems,10 the extensive studies reported by Micheel and his coworkers will be discussed. 

As might be expected the reactivity ratios are strongly dependent on the solvent system. The amount of styrene in the initial copolymer... 

Table 5.6 The number a of solvent molecules sorbed per phenyl group and the limiting Flory -Huggins parameter x0 for polystyrene-divinylbenzene copolymers- solvent systems (Errede 1989)...

Aggregation numbers and core radii have been investigated in detail for many block copolymer/solvent systems [1, 14-18]. The core/shell structure... 

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