Polymer, branched Interaction parameter

The global solubility parameters of polymers were determined from partial molar enthalpies of mixing [60, 71, 72], from partial molar free energies of mixing [60] and from the polymer-solute interactions parameters [60, 68, 101, 108, 109] all these functions were obtained by GLC. For normal, branched and cyclic alkanes, aromatic hydrocarbons and tetraline in polystyrene, eqns (5.40) and (5.42) yield Sj = 7.6 0.2 and 82 = 7.4 i 0.4 cali/2 "cm /z [60] at an average column temperature of 193°C. The same substances in poly(methyl acrylate) give 82 = 8.7 0.3... 

A different approach to the problem has been adopted by Candau and co-workers (85), They make a useful distinction between the temperature 0 that occurs in their equations as a parameter characterizing the polymer-solvent interactions which may be assumed to be independent of MW or branching,- and the temperatures 0Al and 0a at which A2 =0 and os = I respectively, which do depend on both factors. They assume that the free energy of mixing AGm of nl molecules of solvent with n2 molecules of polymer is given by ... 

The viscoelastic properties of solutions of linear and 4-armed star polybutadienes were studied by Osaki and co-workers (117), who compared the storage and loss shear moduli extrapolated to zero concentration with theoretical values. The results for the branched polymer could be accounted for well in terms of the Zimm and Kilb theory (34) a lower value of the hydrodynamic interaction parameter was indicated for the branched polymer than for the linear one, which may be associated with the higher density of polymer segments in the former. 

Cyclic voltammetric behaviour of redox polymers including PVF has been studied previously in acetonitrile and in water solutions [18]. In acetonitrile, PVF exhibits stable, symmetrically shaped cyclic voltammetry peaks at potentials characteristic of oxidation and re-reduction of ferrocene sites in the polymer film. In aqueous electrolyte solutions, non-symmetrical peaks are evident in both anodic and cathodic branches. Differences in PVF behaviour in the two solvents have been attributed to solvent uptake in the polymer film (lower for aqueous solutions), changes in site-site interaction parameters for the polymer film (attractive for aqueous electrolytes and repulsive for acetonitrile electrolytes), and differences in deswelling processes in aqueous solution in the reduction half of the cycle as compared with the oxidation half (Figure 2.4). Acetonitrile is a better swelling solvent for PVF than water [18] and break in of the spin-coated films usually requires more cycling in water than in acetonitrile. 

The position of the left -hand (thermodynamic) branch of the diagram is defined by the solution concentration, polymer M and the interaction parameters x,- position of the right-hand (optical) one is defined by the instrument s geometry and cell length. The system is considered as optimized if there exists a initial solution concentration range between these two branches where imax = 100%. 

The activity coefficients and interaction parameters w ere also determined for other polymer-solute systems (a) normal, branched and cyclic alkanes and aromatic hydrocarbons in poly (methyl methacrylate) [60,100] ... 

Equation (49) formulated for blends of linear macromolecules also provides the facility to model blends of linear polymers (index L) and branched polymers (index B) synthesized from the same monomer [28]. If the end-group effects and dissimilarities of the bi- and trifunctional monomers can be neglected, the parameter a becomes zero. This means that the integral interaction parameter is determined by the parameter i lb. i c > the conformational relaxation, in combination with the intramolecular interaction parameters of the blend components. Because of the low values of and the first terms in (47) and (48) can be neglected with respect to the second terms (for molar masses of the polymers that are not too low) so that one obtains the following expression ... 

Fig. 13 Flory-Huggins interaction parameters for solutions of linear PI (circles, = 23.2 kg/ mol) and of branched PI (stars, Af = 21.6 kg/mol) in CH as a fimction of polymer concentration...

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