T.D. Ignatova

Comparison of thermodynamic and rheological properties of binary polymer mixtures

Abstract The dependence of viscosity on concentration for a series of binary mixtures of polymers differing in their chemical nature and for mixtures of polymer homologues was compared with the peculiarities of their phase diagrams as well as with the concentration dependence of their thermodynamic interaction parameters. A definite correlation was found between the composition dependence of the viscosity and the thermodynamic state of the system in the melt at a given temperature. The universal character of this correlation was shown both for the mixtures of various polymers and for those of the polymer homologues.

Influence of solid surface on equilibria in polymer mixtures

Abstract The influence of solid disperse particles (aerosil) on phase equilibria in ternary (polymer-polymer-solvent) and binary (polymer-polymer) systems has been investigated using adsorption and gas chromatography techniques. The change in position and shape of the binodal for the ternary systems has been established. The region of thermodynamic compatibility of two polymers in a common solvent is broadened due to the selective adsorption of high molecular weight fraction of one of the polymers, this effect being dependent on the amount of solid particles introduced into the system. For binary systems, the thermodynamic interaction parameters χ 23 have been determined and increasing thermodynamic stability of the mixture in the presence of the solid phase has been discovered. The complicated dependences of the interaction parameters on mixture composition are connected with differences in selectivity of adsorption for various compositions. It is supposed that increased thermodynamic stability of a mixture of two incompatible polymers in the presence of solid is due to the transition of both polymers into adsorption and border layers.

Some peculiarities of thermodynamic behaviour of oligomeric mixtures with specific interactions between components

Abstract Using inverse gas chromatography, the temperature and concentration dependences of the interaction parameter χ 23 were estimated for mixtures of various oligomers capable of specific interaction. Mixtures of polyethylene glycol with polypropylene glycol and polyethylene glycol adipate were studied, including mixtures of polyethylene glycol fractions of different molecular weights. It was found that there is a maximum and a minimum in the temperature dependence of χ 23 , and the bimodal character phase diagrams was established. Experimental data were explained by aggregation or association phenomena in mixtures. The comparison of experimental values of χ 23 with those calculated on the basis of the new Flory theory shows essential differences, especially for enthalpy and entropy contributions, this being explained by the specific interaction between components.

The thermodynamic compatibility of melted components and the crystallinity of the polymer blends produced from them

Reversed gas-chromatography has been used to establish the Flory-Huggins parameter ξ23 for the thermodynamic interaction between the melted components of polyethylene glycol (PEG-15,000) and oligoethylene glycol adipate (OEGA-2000), oligopropylene glycol (OPG-1055) and oligostyrene (PS-3040), and of paraffin with M-270; the same was also established for OEGA-OPG, PEG-2000-PEG-40,000 blends and those of low density PE with polyoxymethylene. The concentration dependence of the crystallinity of all the above systems has been found to be identical with that of their ξ23. The conclusion drawn is a larger crystallinity for the dynamically less stable melt blends in the solid state, while those more stable have a lower crystallinity after cooling.

Thermodynamic and sorption properties of interpenetrating polymer networks based on a polyurethane and a styrene-divinyl benzene copolymer☆

The methods of inverse gas chromatography and the sorption of the vapours of low molecular substances have been used to investigate a system of interpenetrating polymer networks (IPN), namely, a polyurethane with a styrene-divinyl benzene copolymer. The thermodynamic properties of the IPN were first assessed. The existence of a transition region in the IPN was established experimentally and the proportion of it was assessed, together with the excess enthalpy of mixing as a function of composition. On the basis of the experimental data for the sorption of benzene vapour, the diffusion coefficient in IPN and in the individual components was calculated for various relative pressures of the sorbate vapour. The free volume fraction was calculated for the diffusion process by Fujitas method. It was established that the free volume fractions in IPN were not additive.

Formation of a linear-polyurethane-linear-polystyrene blend in situ

Blends of linear poly(urethane) and linear polystyrene formed simultaneously in situ by different mechanisms (radical polymerization and polyaddition) at various initial mixture compositions and initiator and catalyst concentrations have been studied by DSC and light scattering. It has been shown that formation of the poly(urethane)-polystyrene blend is characterized by the same kinetic and thermodynamic features as the previously studied poly(urethane)-poly(methyl methacrylate) system. However, the poly(urethane)-polystyrene blend forms much slower than the poly(urethane)-poly(methyl methacrylate) blend owing to different reactivities of the starting components, which are determined by their chemical nature. Phase separation in the poly(urethane)-polystyrene system, which at initial stages proceeds via the spinodal mechanism, occurs much faster than that in the poly(urethane)-poly(methyl methacrylate) system because of a poor mutual solubility of the poly(urethane) and polystyrene being formed and probably because of a higher mobility of their macromolecules at the onset of phase separation.

The thermodynamic and rheological properties of polymer melt mixtures

Abstract Melts of polymer mixtures have been found to possess a correlation between their rheological properties and thermodynamic stability. Regardless of the phase of the mixture components (both crystalline or amorphous, or one crystalline, the other amorphous), a low thermodynamic stability of the system will mean a substantial reduction of the viscosity below that of additivity, and vice versa. An attempt is being made to explain the observed mechanism by the type of phase separation mechanism of such systems.

Some features of the thermodynamic reactions between components in oligomer-polymer homologue mixtures as functions of concentration and temperature☆

Abstract Reverse chromatography has been used on some two-component oligomer systems with specific interactions between the components and on polymer-homologue mixtures of polyethylene glycol and polystyrene to study the temperature and concentration dependences of the thermodynamic reaction parameters. A number of anomalies have been detected in the thermodynamics which can be described within the terms of the Flory theory, but also those of the new Huggins theory. Where the polymer homologue mixtures have fairly contrasting thermal expansion coefficients of the components these can be said to be thermodynamically incompatible unless there exist specific reactions between the components.

Features of the in situ formation of a linear poly(methyl methacrylate)-crosslinked polyurethane blend in the presence of an oligomeric initiator

The process of the in situ formation of a linear poly(methyl methacrylate)-crosslinked polyurethane blend in the presence of different amounts of an oligomeric azo initiator containing fragments of a polyurethane chain and groups capable of initiating the radical polymerization of methyl methacrylate has been studied. It has been shown that the use of an azo initiator providing for the formation of block copolymers retards the phase separation in the system and favors the formation of a finer blend structure that is characteristic by a domain size several times smaller than that of the pristine blend, without the azo initiator. The optimum azo initiator concentration that results in a better dispersion of polyurethane in poly(methyl methacrylate) has been determined.

Thermodynamic characteristics of some oligomer oligomer mixtures

Abstract A study has been made of the mutual solubility of mixtures of oligomeric poly(propylene glycol) with poly(ethylene glycol adipate) (PEGA) and poly(ethylene glycol) (PEG), and of mixtures of PEG with PEGA. The free energy, entropy and enthalpy of mixing were determined over a wide range of temperatures and compositions by the method of inverse gas chromatography. It is shown that the variation of the thermodynamic parameters of mixing is not accord with that predicted by the current theories of mutual solubility of polymers and of solutions of polymers in low molecular solvents.