Abstract
Purpose: Poly (3-hydroxybutyrate-hydroxyvalerate) displayed high dipole-dipole interaction, a high hydrogen bonding but low polar interaction, and was therefore expected to be miscible with solvents/plasticizers that exhibit similar pattern of cohesive interaction. To determine the applicability, or otherwise of the theory of the three dimensional solubility parameters to the formulation of poly (3-hydroxybutyrate-hydroxyvalerate) polymeric coating system, and hence identify any limitation in the application of the theory. This aspect was investigated in the study. Method: The structural group contribution method was employed to compute the partial and total solubility parameters of the compounds – the biopol polymer, a series of organic solvents and plasticizers. The computed partial solubility parameters included: dipole-dipole (dd), polar (dp) and hydrogen bonding (dh). Following a standard procedure in the literatures, the dd and dp values were combined to form a composite solubility parameter, dv: where dv = √ δd 2+δp 2. A plot of dh versus dv gave the energy maps, which depicted the energy levels of the various compounds and from which the miscibility of the compounds were predicted. The closer the position of the solvent or plasticizer to the polymer in the map, the greater, the probability of mixing. Cast films of the various polymeric formulations were made and examined for homogeneity by scanning electron microscopy. Results: It was possible to select suitable plasticizers that were miscible with the polymer by applying theory of solubility parameters. The prediction for the solvents was, however, erroneous and this may be attributable to the inability of the dv parameter to clearly reflect the differences between the dd and dp interactions of the polymer on the one hand and those of the various solvents in all situations on the other hand. This means that in certain instances, the dv values of the polymer and the solvents were similar even though their dd and dp interactions were dissimilar. Conclusion: The analysis of the data showed that the composite solubility parameter dv of compounds could be similar even though the actual energies of dd and dp interactions are different. This is a limitation in the application of the theory of the three dimensional solubility parameters. Keywords: keyword; keyword; keyword > Tropical Journal of Pharmaceutical Research Vol. 4 (1) 2005: pp. 355-362
Highlights
IntroductionThe term solubility parameter (δ) is defined as the square root of the cohesive energy density (E/V) of a compound[1], :
The term solubility parameter (δ) is defined as the square root of the cohesive energy density (E/V) of a compound[1], : = E /V (1)where E is the molar cohesive energy of a compound of molar volume, V
The total solubility parameter is applicable to non-polar compounds only where the dipole-dipole interaction is predominant over other forces of interaction[6]
Summary
The term solubility parameter (δ) is defined as the square root of the cohesive energy density (E/V) of a compound[1], :. Rowe applied the energy maps of the two dimensional solubility parameters to predict miscibility between ethyl cellulose and hydroxypropyl cellulose and the miscibility of plasticizers with the polymer blends[7] Such two dimensional based maps could not be used to select or predict the solvents and plasticizers that are miscible with the acrylatemethacrylate copolymer where the dipole-dipole interactions are considerable and should be considered with the other forces of interaction in the simulation. With this type of compounds, the three dimensional solubility parameters is applied whereby the δd and δp interactions are combined to form a composite solubility parameter designated δv[8]. The formulation of poly (3-hydroxybutyratehydroxyvalerate) polymeric coating system is used as a case in point
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