The miscibility and intermolecular interaction between two uncharged polymers, poly(ethylene-co-propylene) (EPC) and poly(alkyl methacrylates), namely: Poly(methyl methacrylate) (PMMA), poly(dodecyl methacrylate) (PDDMA) or poly(octadecyl methacrylate) (PODMA), in dilute xylene solution at 30 °C were thoroughly investigated by the viscosity measurements. These polymers are mostly used as a lubricating oil additives for rheology properties improvements, particularly the viscosity, temperature dependence of viscosity and pour point depresance, and thus extend the temperature range over which they can be used. The molecules of two polymers, when reaching the point at which the distance between dispersed molecules in dilute solution is of the order of their diameters, will undergo strong mutual attraction or repulsion according to their miscibility. The specific, reduced and intrinsic viscosity and the interaction parameters for above described polymer mixture have been experimentally measured for the binary (polymer/solvent) as well as for the ternary (polymer-1/polymer-2/solvent) systems and also theoretically evaluated for the latter. The interaction between the molecules of two examined polymer mixture leads to the change of the effective hydrodynamic volume of their macromolecules, and thus will influence the solution viscosity. The plot of reduced viscosity of different polymer mixtures composition (WEPC = 0.0 - 1.0) against concentration (γ = 0.5 - 2.0 × 10-2 g cm-3), follows the familiar pattern of the linear plots over the entire range of concentrations, laying between the highest EPC value and lowest PAMA values, and shows an increase as the content of EPC in the mixtures increases (Fig. 1). The experimental values follow the typical linear relationship of the Huggins equation found for the flexible uncharged polymers. The change in the slope of the curve (bm) is attributed to the mutual interaction of macromolecules in solution. At high concentration, the macromolecule chains have increased hydrodynamic volume, which leads to the increasing slope of the ηred vis-a-vis polymer mixtures concentration. The intrinsic viscosities as well as the values of Huggins constants for the all polymer-polymer mixtures was established (Fig. 2, Table 1). It was found that the intrinsic viscosities arise as the WEPC increases, whereas the Huggins parameter, KH, follows the curve showing a minimum at about w = 0.5/0.5 of the polymer mixture composition. This observation indicates a strong composition dependence of intermolecular interaction between EPC and PAMA molecules. According to the criteria proposed, as the difference between the experimental and theoretical (ideal) values of intrinsic viscosities, Δ[η] are positive, the examined mixture could be considered as inmiscible one. The specific viscosities of the polymer mixture of EPC and PMMA, PDDMA or ODMA obtained as the experimental results and calculated applying two theoretical equations, the Catsiff-Hewett and Krigbaum-Wall, were plotted against different weight fraction of EPC (WEPC = 0.0 - 1.0) and over all concentration of 0.5, 1.0 and 2.0 × 10-2 g cm-3. The experimental results entirely follow the Krigbaum-Wall equation curve at higher concentration, however, at lowest concentration (0.5 × 10-2 g cm-3) the both theoretical curves become closer, and the experimental points follow a mild S-curvature. This observation is probably due to the predominant concentration dependence of the intermolecular excluded volume effect, resulting in the concentration of macromolecular coils and thus the reduction of viscosities at higher concentration in comparison with the values obtained, by using the low weighted additive. The estimation of the miscibility degree of the above polymer pairs have been established also by means of sign of the interaction parameter based on the comparison between experimental and theoretical or ideal values obtained by both Krigbaum-Wall and Catsiff-Hewett viscometric miscibility criteria (Table 2). Both methods provide compatibility prediction in argument with those made with the traditional one. As the all polymer/polymer pairs showed the negative Δb12 values (Δb12 12 the observed inmiscibility behavior follows the order: EPC/PMMA > > EPC/PDDMA > EPC/PODMA, in xylene as a solvent at 30 °C and in the assayed composition range (Fig. 5 and Fig. 6). These results show that the bulkiness of the methacrylate units in PAMA play an important role in the interpolymer interaction with polyolefines.
