Thermodynamic properties Polymer-solvent interactions

The alternative value, which describes the polymer-solvent interaction is the second virial coefficient, A2 from the power series expressing the colligative properties of polymer solutions such as vapor pressure, conventional light scattering, osmotic pressure, etc. The second virial coefficient in [mL moH] assumes the small positive values for coiled macromolecules dissolved in the thermodynamically good solvents. Similar to %, also the tabulated A2 values for the same polymer-solvent systems are often rather different [37]. There exists a direct dependence between A2 and % values [37]. 

Charlet, G. Ducasse, R. Delmas, G., "Thermodynamic Properties of Polyolefin Solutions at High Temperature 2. Lower Critical Solubility Temperatures for Polybutene-1, Polypen-tene-1 and Poly(4-methylpentene-1) in Hydrocarbon Solvents and Determination of the Polymer-Solvent Interaction Parameter," Polymer, 22, 1190 (1981). 

The binary interactirMi generally refers to the interactions between polymer-polymer and polymer-solvent The nature of solvent-polymer interaction plays an important role in the miscibility of blends. Many thermodynamic properties of polymer solutions such as solubility, swelling behavior, etc., depend on the polymer-solvent interaction parameter (y). The quantity was introduced by Flory and Huggins. Discussions of polymer miscibility usually start with Flory-Huggins equation for free energy of mixing of a blend (refer to Chap. 2, Thermodynamics of Polymer Blends ). 

PAT Patterson, D., Bhattachaiyya, S.N., and Picker, P., Thermodynamics of chain-molecule mixtures heats of mixing Unear methylsiloxanes, Trans. Faraday Soc., 64, 648, 1968. 1968SEE Seeley, R.D., Thermodynamic properties and polymer solvent interaction parameters for silieone rubber netwoiks. Rubber Chem. Technol, 41,608, 1968. 

Polymer solution viscosity is an important physical property in polymer research, development, and engineering. When high molecular weight nonionic polymer molecules dissolve in a fluid, they typically expand to form spherical coils. In dilute solutions, the volume associated with each polymer coil contains one polymer molecule surrounded by a much larger mass of solvent. A polymer coil s hydrodynamic volume depends upon the polymer molecular weight and its thermodynamic interaction with the solvent. Polymer-solvent interactions depend upon the polymer molecular structure, chemical composition, solution concentration, solvent molecular structure, and the solution temperature. 

Since the value of (r ) is a property of the polymer only, depending as it does only on chain geometry, it follows that the condition of the polymer at the 6 temperature in different solvents is exactly the same. The polymer behaves as though it were thermodynamically ideal showing no interaction at all with the solvent. 

Several block and graft copolymers have been shown to form stable aggregates under thermodynamically poor solvent conditions, as a result of differences in the solubility of different parts of a macromolecule. Whereas in a good solvent the experimentally measured value of A2 for a copolymer represents the balance of all the multiple interactions, under thermodynamically poor conditions A2 is mainly determined by the interaction of the groups situated on the polymer-solvent interface. Groups which form the hydrophobic core and are not in a contact with the solvent do not contribute significantly to the solution properties of the copolymer. 

In those cases in which V2/Vi is known, both gv° and g ° are given. For the rest of the systems, only gv° is given. Prediction of thermodynamic properties on ternary systems formed by a polymer and two solvents or two polymers and a solvent requires the knowledge of the parameter g°, characteristic of the interaction of the corresponding binary pairs [9], However, due to the variety of sources for the several systems studied, the data correspond to different polymer molecular weights, m, and to different temperatures. Since the variation of x with concentration may depend on M for low M s, it has selected data only for M > 2 x 109, where no M dependence is detected. 

Flory (1942) noted that the combinatorial term is not sufficient to describe the thermodynamic properties of polymer-solvent systems. To correct for energetic effects, he suggested adding a residual term, ares, to account for interactions between lattice sites. 

Group contributions for the interaction energy, ekk T, the surface area, Qk, and the reference volume, Rk, for the High-Danner model have been calculated for the alkanes, alkenes, cycloalkanes, aromatics, esters, alcohols, ethers, water, ketones, aromatic ketones, amines, siloxanes, and monochloroalkanes. If solvents and polymers of interest contain these building blocks, the thermodynamic properties can be calculated. More detailed information concerning the High-Danner equation of state is given in Procedure 3E. 

The failure of the van Laar model to give realistic predictions of the thermodynamic properties of polymer solutions arises from the assumption made in this model that the solvent and solute molecules are identical in size. However, Flory [1] and Huggins [2] proposed, independently, a modified lattice theory which takes into account the large differences in size between solvent and polymer molecules, in addition to Intermolecular interactions. 

Molecules in the dissolved, molten, amorphous, and glassy states of macromolecules exist as random coils. This is a result of the relative freedom of rotation associated with the chain bonds of most polymers and the myriad number of conformations that a polymer molecule can adopt. As a consequence of the random coil conformation, the volume of a polymer molecule in solution is many times that of its segments alone. The size of the dissolved polymer molecule depends quite strongly on the d ee of polymer-solvent contact. In a thermodynamically good solvent, a high degree of interaction exists between the polymer molecule and the solvent. Consequently, the molecular coils are relatively extended. On the other hand, in a poor solvent the coils are more contracted. Many properties of macromolecules are dictated by the random coil nature of the molecules. We now discuss briefly the conformational properties of polymer chains. 

Starting from a thickness of 0.3 x 10 m, the properties of the boundary layer of the polymer approach the voliunetric values. The data enable determination of specific changes of the retention voliune Vg with change in the film thickness. For the polymer located on the surfactant-treated basalt surface we observe a neghgible change of Vg with variation of the film thickness. When the imtreated basalt flakes with a film thickness of 0.03 x 10 m are used, we observe a sharp increase of Vg that can be explained by the decrease of structme density. Figure 9.2 presents the dependence of the thermodynamic interaction parameter of polymer solvent Xi,2 the film thickness. As is... 

Also for polymer solutions, the properties depend on interactions between solvent and dissolved components and vary strongly with concentration and temperature. Therefore, beside the molecular analysis, there is the important question for the understanding of the relationship between structure and properties, whether and how PLCs in a solution can be distinguished from those containing non-liquid crystalline polymers with a similar molecular architecture. Another interesting question is, to what extent the conformation of the macromolecules in solution is influenced by interactions between mesogenic groups. As a consequence of that, the hydro- and thermodynamic properties of the solution should also be affected. 

In these considerations the solute practically plays no part in the thermodynamic properties of the system. When separation occurs in polymer solutions, however, the high polymer substance itself is determinant for the thermodynamic behaviour and we must apply the theory of section 7. a. 1, taking into account that the interaction constant 7 changes with temperature (see below). Experiments with polythene in various solvents are in fair agreement with Huggins and Flory s theory. Discrepancies are attributed partly to the non-uniform molecular weight of the solute. 

The two monomers of major interest, styrene and ethylene, are well known and details can be found on all aspects of their technology elsewhere. Poly(ethylene-co-styrene) is primarily produced via solution polymerization techniques using metallocene catalyst/co-catalyst systems, analogous to the production of copolymers of ethylene with a-olefin monomers. Solvents that can be employed include ethyl-benzene, toluene, cyclohexane, and mixed alkanes (such as ISO PAR E, available from Exxon). The thermodynamic properties of poly(ethylene-co-styrene), including solvent interactions and solubility parameter assessments, are important factors in relation to polymer manufacture and processing, and have been reported by Hamedi and co-workers (41). 

---