Solvent and Polymer Molecular Weight

Non-annealed devices are labeled nA and annealed devices are labeled AC . Adapted from Ref. [57] with permission of John Wiley Sons, Inc. 

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In systems where the interactions are dominated by the van der Waals forces, solubility is favored by chemical similarity of solvent and polymer. Molecular weight, chain branching and cross-linking of individual polymers slightly influence the solubility parameter, 5 [Hildebrand, 1916]. In a strict sense, the molecular interactions should be non-specific, without forming associations or orientation, hence not of the hydrogen or polar type. The intermolecular interactions 1-2, are assumed to follow the geometric mean of the intramolecular interactions, 1-1 and 2-2 ... 

Important factors are concentration, temperature, nature of both solvent and polymer, molecular weight of the polymer, among others [16-21]. 

Although instances of lyotropic PLCs predate studies of thermotropic PLCs, as they involved solutions of comparatively esoteric species — virus particles and helical polypeptides — studies of these liquid crystals were isolated to a few laboratories. Nevertheless, observations on these lyotropic PLCs did stimulate the first convincing theoretical rationalizations of spontaneously ordered fluid phases (see below). Much of the early experimental work was devoted to characterizing the texture of polypeptide solutions. (23) The chiral polypeptides (helical rods) generate a cholesteric structure in the solution the cholesteric pitch is strongly dependent on polymer concentration, dielectric properties of the solvent, and polymer molecular weight. Variable pitch (<1 - 100 pm) may be stabilized and locked into the solid state by (for example) evaporating the solvent in the presence of a nonvolatile plasticizer.(24)... 

Table 8.1 Mobility of holes and electrons in P3HT, [60JPCBM, and P3HT [60]PCBM blend OFETs using different solvents and polymer molecular weights.

Most fibers and films of PAn have been prepared from a solution of emeraldine base and converted to the emeraldine salt by acid doping. The choice of dopant acid has a profound effect on mechanical properties. In fact, MacDiarmid et al. have shown that the mechanical properties depend in a complex way on dopant, casting solvent and polymer molecular weight. Full details of the effects of polymer structure (as influenced by dopant and solvent) on the mechanical properties are yet to be eludicated. 

Some complexes dissociate fully in solution (e.g., 7r-allyl nickel tri-fluoroacetate) whence [63] Rp cc [C2][M]. Donor solvents (triphenyl-phosphite, nitrobenzene) can also coordinate with the metal and influence catalyst dissociation with effects on rate and polymer molecular weight the structure of the polymer may also be affected [173]. 

The molecular clustering in systems composed of low molecular weight solvents and high molecular weight polymers, proteins, etc., has been investigated both experimentally and theoretically. The present paper is focused on the theoretical investigation of clustering on the basis of the fluctuation theory... 

A theoretical treatment of aqueous two-phase extraction at the isoelectric point is presented. We extend the constant pressure solution theory of Hill to the prediction of the chemical potential of a species in a system containing soivent, two polymers and protein. The theory leads to an osmotic virial-type expansion and gives a fundamentai interpretation of the osmotic viriai coefficients in terms of forces between species. The expansion is identical to the Edmunds-Ogston-type expression oniy when certain assumptions are made — one of which is that the solvent is non-interacting. The coefficients are calculated using simple excluded volume models for polymer-protein interactions and are then inserted into the expansion to predict isoelectric partition coefficients. The results are compared with trends observed experimentally for protein partition coefficients as functions of protein and polymer molecular weights. 

It has been established that Ko normally is independent of the solvent and the molecular weight of the polymer, though often dependent to some extent on the temperature. It is therefore possible to deduce values for the expansion factor in good solvents from intrinsic viscosities measured in them. From Eqs. (3.181) and (3.184) the linear expansion factor a.jj, which is a measure of long range interactions and pertains to hydrodynamic chain dimensions, is thus given by... 

Cobaltocene and related complexes have been incorporated into conjugated polymers. Reaction of cobaltocene-containing polymers 49 (R = aryl) with Tmtylisocyanide gave new metallopolymers, 154 (Scheme 4.34)." These polymers were soluble in organic solvents and had molecular weights of 6800-22,600 Da (Mn, GPC). Polymers 154 could be partially V-methylated with iodomethane. 

Besides the structures already discussed, more complex morphologies may be obtained from the growth of polymer crystals from solutions. The structure that emerges from the crystallization of a polymer is a function of a complex interaction of factors that include the type of solvent, solution temperature, concentration, and polymer molecular weight. Some examples of these structures include spiral growth, dendrites, and hedrites. 

T.ee Lee, B.-C., Lim, J.S., and Lee, Y.-W., Effect of solvent composition and polymer molecular weight on cloud points of poly(L-lactide) in chlorodifluoromethane + carbon dioxide, J. Chem. Eng. Data, 48,774,2003. 

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