Oxazoline-methacrylate graft-copolymers with upper critical solution temperature behaviour in Yubase oil

Abstract

Thermoresponsive behavior of polymers in aqueous solutions has been widely studied and utilized in various applications. However, the fundamental understanding on the use of oil soluble polymers in non-aqueous solutions is very limited. Herein, we report the synthesis of linear homo and copolymers as well as graft-copolymers based on 2-oxazoline monomers and the investigation of their solution behavior and thermal properties via turbidity measurements and thermal analyses (DSC and TGA). The homo and copolymers were synthetized via living cationic ring-opening polymerization (CROP) of 2-stearyl-2-oxazoline (SteOx) and 2-ethyl-2-oxazoline (EtOx) and their composition was varied in order to tune the thermoresponsive behavior in a commercially available base oil (Yubase-4). The graft-copolymers were obtained using the grafting-onto method. The backbone composed of a methacrylic acid and 2-ethylhexyl methacrylate copolymer was synthetized via reversible addition–fragmentation chain-transfer (RAFT) polymerization, while side chains consisting of SteOx–EtOx copolymers were obtained via CROP. Various polymerization parameters were evaluated in order to optimize the grafting efficiency and the solubility in oil of the synthetized graft-copolymers. It was seen that not only the overall hydrophobicity of the polymer chains but also the overall order of the system have significant effects on the upper critical solution temperature (UCST) in oil. Finally, a relationship between the crystallization temperature measured using DSC and the transition temperature (T_trans) values obtained from the turbidity measurements was compared.