Polymer solutions solvent system

In some polymer-nonpolar solvent systems, % has been calculated as a function of concentration on the basis of the statistical-thermodynamical theory called the equation of state theory [13,14]. This semiempirical theory takes into account not only the interaction between solute and solvent, but also the characteristics of pure substances through the equations of state of each component. At present, however, we cannot apply this approach to such a complex case as the NIPA-water system. Thus, at the present stage, we must regard % as an empirical parameter to be determined through a comparison between calculated and experimental results. The empirical estimation of % for the NIPA-water system will be described in the next section. 

The PEG/water, PPG/water, and PVAL/water are among the most extensively studied water-soluble polymer solutions. These systems typically show a closed-loop phase behavior (Figure 16.4). Results for some ternary systems have been reported many of these data are for PEG/Dextran/water and PEG/water/salts and related systems, which are important for separating biomolecules such as proteins. Only few data for PEG or other hydrogen bonding polymer with mixed water solvents have been reported. 

The general idea underlying the preparation of layered clay-polymer intercalates follows the simple rules of ion exchange. In most cases, the synthesis involves either intercalation of a polymer from solution or a suitable monomer followed by subsequent polymerization. But for more technologically important polymers, both approaches are limited since neither a suitable monomer nor a compatible polymer host solvent system is always available. 

The polymer was purified by dissolving the PNF in Freon TA (Miller Stephenson Chemical), followed by mixing in an equal volume of deionized distilled water with the Freon/polymer solution. The system was then allowed to phase separate. The Freon layer was eluted into hexane, causing the high molecular weight polymer to precipitate out. The polymer was then vacuum dried. Solutions of the purified polymer were prepared in reagent-grade acetone. All films were cast from solution in a closed environment to reduce surface contamination and retard the rate of solvent evaporation. 

It should be noted that among the three different methods of PNC preparation mentioned above, the solution method and the in situ polymerization method have only limited applications because neither a compatible polymer-silicate solvent system nor a suitable monomer is always available. Moreover, they are not always compatible with current polymer processing techniques. Among all the methods to prepare PNCs, the approach based on direct melt mixing/intercalation is perhaps the most versatile and environmentally benign. 

The cosolvency phenomenon was discovered in 1920 s experimentally for cellulose nitrate solution systems. Thereafter cosolvency has been observed for numerous polymer/mixed solvent systems. Polystyrene (PS) and polymethylmethacrylate (PMMA) are undoubtedly the most studied polymeric solutes in mixed solvents. Horta et al. have developed a theoretical expression to calculate a coefficient expressing quantitatively flie cosolvent power of a mixture (dTydx)o, where T,. is the critical temperature of the system and x is the mole fraction of hquid 2 in the solvent mixture, and subscript zero means x—>0. This derivative expresses the initial slope of the critical line as a function of solvent composition (Figure 5.4.1). Large negative values of (dT/dx) are the characteristic feature of the powerful cosolvent systems reported. The theoretical expression developed for (dT dx)o has been written in terms of the interaction parameters for the binary systems ... 

First part of the chapter is devoted to the equilibrium aspects of polymer solutions and factors diat influence miscibility. Influence of polymer type, molecular weight, concentration, nature of the fluid and its composition, temperature and pressure are demonstrated with selected polymers and solvent systems. A particular focus of the chapter is on the ternary systems that deal with the miscibility of polymers in binary fluid mixtures of caibon dioxide with an organic solvent, or the miscibility of two different polymers that are mutually incon atible, in a common solvent. The specific examples that are discussed are systems such as (1) polyolefin + alkane + carbon dioxide (2) copolymer elastomer + alkane + carbon dioxide (3) cellulosic polymer + polar solvent + carbon dioxide and (4) polyethylene + polypropylene + alkane. 

If the flexible polymer is placed in a better" solvent where there is much interaction between solute and solvent, then the radius of gyration will Increase more rapidly with M. As a is dependent on molecular weight, it will also increase. Tire maximum value of the exponent a in good solvents is 1.0. The parameters K and a are are determined by measurements of (iiJ for each solute-solvent system using for calibration samples of known molecular wei t. 

The theta temperature is different for each combination of polymer and solvent. Table 2.6 lists for some polymer solutions." Each system has its own theta temperature, although it may not be reached in the liquid phase of the solvent or below the decomposition temperature of the polymer. 

This has an important implication, especially for polymer systems. The diffusion coefficient of typical solute solvent systems is on the order of 10" cm ... 

There are concerns over polymer solution-based systems (eg, electrospinning) that are used to produce nanofibres. Solvent handling has safety concerns for production operatives and presents certain difficulties, eg, storage of volatile liquids. The recovery of solvents is expensive and adds significant costs to the economics of the process. 

We now turn from binary polymer solvent systems to ternary polymer matrix solvent systems. Dielectric relaxation studies using polyisoprenes as probe chains in polybutadiene -heptane solutions were examined by Urakawa,... 

In recent years, studies of solutions of polymer blends and of copolymers have aroused a substantial theoretical and experimental interest. This is motivated by both numerous applications and more fundamental issues concerning the usefulness of the scaling and universality concepts to describe the thermodynamic properties and the phase transitions in these systems. In this lecture, chain interactions in dilute and semidilute solutions are reviewed and it is discussed how and when the interactions between chemically different monomers lead to a macroscopic phase separation in the case of ternary polymer A-polymer B- solvent systems and to a mesophase formation in diblock-copolymer solutions. The important conclusion is that due to both the overall monomer concentration fluctuations (excluded volume effects) and the composition fluctuations, the classical Flory theory often fails. This requires the use of the renormalization method and of scaling concepts to give a correct description of the phase diagrams and the critical phenomena observed in these complex systems. We give only here a brief outline, a complete review has been published elsewhere, ... 

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