The influence of the molecular weight of polyvinylpyrrolidone (PVP) on the molecular mobility and physical stability of indomethacin (IMC)-PVP solid dispersions was investigated over a wide temperature range in the supercooled state. As the polymer molecular weight increased, there was a decrease in molecular mobility as evident from the longer α-relaxation times. Inhibition of IMC crystallization also increased as a function of polymer molecular weight. The extent of H-bonding interaction between drug and polymer, quantified by ssNMR, was independent of polymer molecular weight. Over a polymer concentration range of 5-20% w/w, the temperature dependence of mobility and viscosity was reasonably similar for different grades of PVP. It was concluded that the increase in effectiveness in crystallization inhibition as a function of polymer molecular weight is due to the increased viscosity, which slows down the mobility of these systems.
Bibliographical noteFunding Information:
This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We are thankful to Dr. Gregory Halder and Dr. Wenqian Xu at Argonne National Laboratory for their help during the synchrotron data collection. The project was partially supported by the William and Mildred Peters endowment fund.