Structural and Rheological Properties of Polyacrylate Homopolymer Upon Thermal Manipulation

Nova Southeastern University, Davie, Florida, USA

Objective. Evaluate the structural and solution flow properties of Carbopol 981, upon thermal treatment of the solid polymer. Background. Polyacrylate polymers are viscosifying agents that could be utilized in the development of extraction-resistant abuse-deterrent formulations (ADFs). In this study, we evaluated the tolerance of the polymer to thermal manipulation, indicated by its structural and rheological stability. Methods. Solid Carbopol 981 was heated (air-circulated oven, 80 and 180 C, 1 hr.); the polymer (125mg) was dissolved in 25 mL solvent (water, 40% v/v ethanol, and saline), and the mixtures were adjusted to pH 6–7 using NaOH. Non-treated control samples were also prepared. The rheological properties of the prepared solutions were measured using a cone & plate rheometer at 25°C. The structural stability of the solid polymer samples was assessed using DSC and FTIR. Results. Changes in solution viscosity between the control and heated polymer at 80oC were <20% in all solvents, with pseudoplastic flow behaviour over the shear rate of 37-1537 sec-1. On the other hand, the aqueous mixtures of the heated polymer at 180oC showed significant reduction in viscosity along with polymer precipitation. Reproducible results could not be obtained for such samples due to the presence of solid powder in solution which interfered with the measurement. The DSC and FTIR analysis confirmed structural changes with the 180°C-heated powder. Conclusion. Carbopol 981 is sensitive to thermal manipulation at high temperatures, rendering the carbopol-based compositions abusable by the intravenous route. Grants. NSU Grant 335081.