A combination of vapor sorption and dynamic laser light scattering methodsfor the determination of the Flory parameter Chi and the crosslink densityof a powdered polymeric gel

Reliable techniques can be easily used to determine the crosslink density a nd the Flory interaction parameter of polymeric gels, on condition that mon olithic matrices of the crosslinked polymer are available, but they cannot be profitably applied to powdered forms. In the present work we propose an experimental procedure which is particularly suitable to determine the abov e mentioned parameters in the case of polymeric gel particles. The techniqu e is based on polymer swelling experiments performed in the presence of vap our and liquid external phases, and was applied to four different commercia l types of sodium starch glycolate. Such a crosslinked polymer is normally supplied in a powdered form and commonly used in the pharmaceutical field a s disintegrant in tablet formulation. For each polymer, the crosslink densi ty rho(X) and the Flory interaction parameter X were calculated from the ex perimental swelling data by solving the relevant equilibrium equations deri ving from the Flory theory for gel/liquid and gel/vapor equilibrium conditi ons. The crosslink density values were then used to estimate the mesh size of the polymeric networks. Such a parameter is of great interest in the pha rmaceutical field since it can play an important role in the performance of drug release systems based on polymeric gel matrices or minimatrices. (C) 2000 Elsevier Science B.V. All rights reserved.