Article

 

Interaction Parameter (Χ); Expansion Factor (ε); Steric Hindrance Factor (σ); and Shielding Function F(ξ); for the System PEA-Organic Solvents by Intrinsic Viscosity Measurements

 

Martha L. Cecopieri-Gómez*^,a and Joaquín Palacios-Alquisira^b

 

^a Instituto Mexicano del Petróleo, Research and Development Program in Molecular Engineering, Lázaro Cárdenas 152, Col. San B. Atepehuácan, 07730 México D. F., México. * e-mail: mcecopie@imp.mx

^b Universidad Nacional Autónoma de México, Chemistry Faculty, Macromolecular Physicochemistry Department. "D" Building, Lab. 108, Cd. Universitaria, 04510 México D. F., México

 

Received: November 5, 2004
Published on the web: April 26, 2005

 

Abstract

In this work we present experimental data of the Flory binary interaction parameter, χ, of poly (ethylene adipate) PEA, a plasticizer material. We have used the viscometric method for measuring dilute PEA solutions in good solvents: benzene, chloroform and acetone. A procedure based on the Stockmayer-Fixman, (SF), hydrodynamic solutions theory, allows us to evaluate some thermodynamic parameters via the intrinsic viscosity [η], measured in several good solvents. This method also estimates the unperturbed parameter, k_θ, and the steric hindrance parameter, (σ), by viscosity measurements at constant temperature of 30°C. By correlation of the molecular weight (M) and intrinsic viscosity data, according to the Stockmayer-Fixman (SF) solution theory model, values of Flory binary interaction parameter χ, equal to χ_1,2 =0.1544 ± 0.01; χ_1,2 =0.1631 ± 0.01; and χ_1,2 =0.1922 ± 0.01, for PEA in benzene, chloroform and acetone, respectively, were obtained. In addition we applied the Debye-Bueche theory, in order to estimate values of: expansion factor (ε), shielding factor (ξ) and depth of shielding (L) for the system PEA-organic solvents, by [η] and (M) experimental data correlation. The results confirm that values obtained, correspond to "good solvents" for the PEA polymer.

Keywords: Flory binary interaction parameter, hydrodynamic properties of poly(ethylene adipate), Stockmayer-Fixman (SF) hydrodynamic model, Debye-Bueche solution theory, intrinsic viscosity

 

Resumo

Medidas viscosimetricas de PAE, poli(adipato de etileno), em benzeno, cloroformio e acetona a 30 °C foram utilizadas para determinar experimentalmente os parâmetros binários de interação de Flory (χ_i,j), para esse material plastificante. Obtiveram-se valores de χ_1,2 =0,1544 ± 0,01, χ_1,2 =0,1631 ± 0,01, e χ_1,2 =0,1922 ± 0,01, para o PAE em benzeno, cloroformio e acetona respectivamente, mediante correlação de dados de peso molecular (M) e viscosidade intrínseca [η] de acordo com o modelo hidrodinámico de Stockmayer-Fixman (SF) para soluções poliméricas diluídas. O modelo permite também estimar o parâmetro constante, k_θ para a combinação polímero (1) - solvente (2) no estado tetha (θ) e o parâmetro de impedimento estérico (σ). Neste trabalho reporta-se os valores para o parâmetro binário de interação de Flory, que apontam que os solventes utilizados, são termodinamicamente, bons solventes para o PAE. Adicionalmente, mediante a aplicação da teoria de Debye-Bueche aos dados experimentais de [η] e (M), estimaram-se os fatores de expansão (ε) e proteção (ξ) e a profundidade de proteção (L), quantidades que confirmam que os solventes empregados são bons solventes para o sistema PAE.

 

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