Yu.S. Bessonov

Thermodynamics of mixing polymers

Abstract Free energies Δg x , enthalpies Δh x and entropies TΔs x of mixing were calculated for eight polymer-polymer systems. It was shown that the polymer compositions studied, in respect of the shape of the curve showing the concentration dependence Δg x , may be classified in three groups: stable, metastable and unstable. For a stable cellulose nitrate-polyvinylacetate system a reduction in entropy was observed during mixing, which may be due to ordering of elements of the system. For metastable systems thermodynamic functions of mixing Δh x and TΔs x are positive in one range of composition and negative in the other. An unstable polymethylmethacrylate-polybutylmethacrylate system undergoes endothermic mixing over the entire range of composition and the free energy varies positively and entropy of mixing increases in this case.

The thermochemistry of polymer solutions and compositions in the phase separation region

The heats of mixing of oligomeric polyoxypropylenediol (POPD) with water and of the following polymers: cellulose nitrate (NC) with polyvinylacetate (PVA), NC with cellulose acetate (CA), CA with PVA and polyvinylchloride (PVC) with polymethyl-methacrylate (PMMA) have been obtained in the region of phase separation. For the polymer compositions the heats of mixing were calculated according to Hesss law, fow which the heats of solution of the polymers and polymer mixtures in a common solvent were determined. The POPD-water system, which has a lower critical temperature of mixing (LCTM) is exothermic over the entire range of compositions and temperatures. At T LCTM) the curves contain a linear section. The curves of the concentration dependence of the enthalpy of mixing of NC with PVA are uninterrupted and the system is exothermic. The enthalpy of mixing-composition curves of the other polymer compositions contain a linear section, indicating phase separation. Analysis of the curves showed that the temperature coefficients of solubility of each component in the two layers have the same sign, which is possible only if there is one sided diffusion of one of the components. From the evidence presented it follows that PVC diffuses into PMMA, CA into NC and CA into PVA. This is accompanied by loosening up of one part of the transitional layer (in which diffusion takes place), with an endothermic effect, and compacting of the other part of the transitional layer, with an exothermic effect. This is in good agreement with the ideas developed by Voyutskii and Kuleznev.

Thermodynamic studies of reactions in filler containing polyvinyl chloride

Abstract Microcalorimetry and isothermal sorption have been used to study the enthalpy, free energy and entropy of the PVC reactions with aerosil, white carbon, chalk and kaolin. The thermodynamic parameters of these reactions were found to change a lot with the amount of filler and its chemistry. Negative heats and entropies of reaction in the range of low filler contents other than chalk are explained by the formation of adsorbed and oriented PVC layers on the filler surfaces. The positive values of these are typical for the system PVC-chalk as well as for larger contents of aerosil, white carbon and kaolin; they indicate the lack of any thermodynamic affinity of the components for each other and the thermodynamic instability of such compositions.

Effect of the thermodynamic affinity of plasticizers for polyvinyl chloride on the heat of its interaction with fillers

Abstract A microcalorimeter of the Calve type has been used to determine the heats of swelling of PVC in four plasticizers and heats of wetting by the latter of chalk, kaolin and Aerosil and the heats of the interaction of plasticized PVC with these fillers. It is shown that the energy interaction of PVC with the filler is due to the competing influence of its heats of swelling in the plasticizers and the heats of wetting by the latter of the fillers. For identical thermodynamic affinity of the plasticizers for PVC the global thermal effect of the interaction of plasticized PVC with filler is more negative the greater the heat of wetting by the plasticizer of the filler. For identical heats of wetting by the plasticizers of the PVC filler the worse PVC interacts energetically with the filler, the greater the thermodynamic affinity of the plasticizer and the greater the heat of swelling of PVC.

Thermodynamic study of blends of polymethylmethacrylate with copolymers of methylmethacrylate and butylmethacrylate

Abstract Successive interval sorption and microcalorimetry have been used to determine the mean Gibbs energies Δg x and the enthalpies Δh x of mixing PMMA with the statistical copolymers of methylmethacrylate and butylmethacrylate of different composition. The mixing entropies are calculated. It is shown that PMMA is incompatible with copolymers containing 50 and 75% by weight of butylmethacrylate. The compatibility of PMMA with copolymers with a smaller amount of butylmethacrylate (10 and 25%) is observed only for certain component ratios. It was found that the formation of compatible blends is accompanied by positive values of mixing entropy, enthalpy, and TΔS x > Δh x . The transition from compatibility to incompatibility at which Δg x changes sign as a result of the balance of the enthalpic and entropic terms is of a critical nature.

The thermodynamics of the interactions in filled plasticized polyvinylchloride compositions

Abstract Microcalorimetry and isothermal sorption have been used to study the enthalpy, free energy, and entropy of the reactions of di-octyl sebaceate modified PVC with chalk and Aerosil as filler. The di-octal sebaceate (DS) has been found to have little affinity for the PVC. The introduction of the fillers into the plasticized PVC variously affected the thermodynamic interaction parameters. The production of the PVC-DS-chalk composition has been found to be accompanied by positive values of all the thermodynamic interaction parameters; there is a dominant disarrangement of the polymer matrix. In the case of the PVC-DS-Aerosil composition the parameters were negative and this was enhanced by increasing the filler content. Competition has been found to exist between the PVC-DS, PVC-Aerosil, and DS-Aerosil contacts, so that an energetical interaction between DS and the Aerosil became dominant and resulted in better order in the system and in an improved thermodynamic stability.

Heats of solution of cardo-polyheteroarylenes and the effect of individual macromolecular groups☆

Abstract A study was made of heats of solution and swelling in dimethylformamide and tetrachloroethane of a number of polyarylates, aromatic polyamides and tetrachloroethane of a number of polyarylates, aromatic polyamides and polyimides, the macromolecules of which contain phthalide, fluorene and anthrone cardo-groups. The interaction of all polymers studied with DMF and tetrachloroethan is normally accompanied by considerable exothermic effects. Heats of solution or swelling are additive and formed of heats of interaction with these solvents recurrent in the chain of aromatic acid, diamine and bisphenol residues.

The effect of molecular weight and pore structure on the thermodynamic solubilization parameters of carding polyarylate

The integral heats of solubilization of polyarylate fractions have been determined and the sorption of chloroform vapours by samples of various molecular weights and porosities investigated. The true density of the polymer was found to diminish as the molecular weight (mol.wt.) increased, while the heat of solubilization became more negative; it became constant from M = 70,000 upwards. Porosity differences did not affect the heat of solubilization. The thermodynamic affinity parameters of the polyarylate for the solvent (the free energy of mixing and reaction parameter χ1) depend on the pore structure of the polymer in the range of concentrations by weight of ω2 < < 0·05, so long as the polymer-solvent systems remain in the glass-like state at the experimental temperature.

Thermodynamics of the solution of card polyarylates in chloroform and tetrachlorethane

Abstract Free energies, enthalpies, entropies of mixing of two polyarylates (P-2 and D-9) in tetrachlorethane (TCE) and chloroform were determined. It was shown that TCE is a more satisfactory solvent than chloroform for both polymers. Both polymers dissolve in both liquids with very high exothermal effects and reduced entropy. The heat and entropy of solution of D-9 in CF are more negative than in TCE, which is the consequence of partial crystallization in this solvent.

Thermodynamic study of solutions of polyvinyl acetate and cellulose tricarbanilate in the pre-critical region☆

It has been found that endothermic mixing occurs in the pre-critical region in the polyvinylacetate (PVA)-methanol system, which has an upper critical temperature of mixing (UCTM) (Δhm>0 and∂2Δhm∂x22 0). Consequently for these two systems, with liquid phase separation, there are thermodynamic criteria of the UCTM and LCTM. In the system CTC-cyclohexanol, in which crystalline phase separation occurs, these criteria are not present. The mixing volumes were determined and the internal pressures and energies of mixing were calculated for all the systems. It was found that Δhpm≠ΔUνm, corresponding to exothermic mixing in the CTC-cyclohexanol system, is due to contraction of the system on mixing. The internal energy of mixing of this system is positive.