DETERMINATION OF SOLUBILITY PARAMETERS OF POLYMERS BY USING INTRINSIC VISCOSITY METHOD
Advancing the chemical engineering fundamentals
Thermodynamics (T2-1P)
Keywords: SBES triblock copolymers, intrinsic viscosity, solubility parameter
The wide use of polymers in many fields emphasizes the need to analyze different polymer properties; one of the most important is the solubility parameter (dp). The objective of this work is to obtain the solubility parameter of a hydrogenated triblock styrene-butadiene-styrene copolymer (SBES), from intrinsic viscosity (IV) measurements at 30ºC.
All viscosity measures were carried out in an Ubbelohde 0b type of capillary viscosimeter. To obtain intrinsic viscosity values from flow time measurement, Huggins and Kraemer equations [1] were used:
Relative viscosity was obtained as the relation between the flow time of the polymer solution through a capillary tube of known diameter and length, and the flow time of the pure solvent. Specific viscosity is defined as relative viscosity minus one and represents the increase in viscosity due to the polymer. So the intrinsic viscosity can be determined as usual as the common intercept of the Kraemer and Huggins relationships, using specific and relative viscosities experimentally obtained.
Related to intrinsic viscosity of a polymer solution, the higher its value is, the more compatible polymer and solvent are. So, the solubility parameter of the polymer was determined by getting the maximum of the plot intrinsic viscosity vs. solvent solubility parameter (ds) [2] (eq. 1). The result obtained was 17.26 MPa^1/2 and is similar to other values found in literature for non-hydrogenated and non-vulcanized (SBS) rubbers [3], and to other found for random (SBR) rubbers [4]. The solubility parameter of polymer is closer to solubility parameter of cyclohexane and cyclopentane what indicates that these solvents are the most compatible with the polymer.
IV = -0.1167dp^2 + 4.027dp - 33.83 (1)
Table 1 The solubility parameter of solvents [5] and intrinsic viscosity.
Solvent ds (MPa^1/2); IV (gdl-1)
n-hexane 14.9; 0.29
methyl-cyclohexane 16.4; 0.84
cyclohexane 16.8; 0.94
cyclopentane 17.8; 0.88
toluene 18.2; 0.80
benzene 18.8; 0.68
References
[1] Bustamante, P. et al, Eur J Phar Sci 2005; 24; 229.
[2] Sheehan, C. J., Bisio, A.L., Rub Chem&Tech 1966: 150
[3] Romdhane I.H., et al., J App Pol Sci 1992; 45: 2049.
[4] Barton, A.F.M., Chem Rev 1975; 75(6): 731.
[5] Brandrup, J., Immergut, E.H., Polymer Handbook, 3ª Edition, 1989.
Presented Monday 17, 13:30 to 15:00, in session Thermodynamics (T2-1P).
