Full-composition-range glass transition behavior of the polymer/solvent system poly (lactic acid) / ethyl butylacetylaminopropionate (PLA/IR3535®)

Abstract

© 2020 Elsevier Ltd The polymer/solvent system poly (lactic acid)/ethyl butylacetylaminopropionate (PLA/IR3535®) is considered as a drug-delivery system, in which a polymer hosts a liquid with a functionality as insect repellent. Such devices require solubility of the components at high temperature and observation of crystallization-induced solid-liquid phase separation on cooling. Precise knowledge of the thermodynamic solubility of the components is then difficult to obtain due to possible superposition of liquid-liquid phase separation with polymer crystallization. Therefore, in the present study the miscibility of the polymer/solvent system PLA/IR3535® was explored by employing non-crystallizable PLA, by analysis of the glass transition behavior in the full composition range. The data revealed that the two components are miscible regardless the system composition, with the glass transition temperature of solutions showing a negative deviation from the linear mixing rule, suggesting rather weak enthalpic interactions of the system components. The study included application of conventional and fast scanning chip calorimetry, which allowed for controlled and stepwise evaporation of solvent by repeated exposing the system to elevated temperature and evaluation of the glass transition temperature during in-between cooling and reheating. This novel approach permits an efficient analysis of the glass transition temperature as function of the system composition in a single experiment in a wide range of solvent concentrations.