Imidazolium‐Based Ionic Liquids as Initiators in Ring Opening Polymerization: Ionic Conduction and Dielectric Response of End‐Functional Polycaprolactones and Their Block Copolymers

Abstract

Imidazolium alcohols, [R‐Im‐Z‐OH]+[X]−, are investigated as initiators for ring opening poly­merization (ROP) of ε‐caprolactone (CL). Two monomeric imidazolium alcohols {I [R = HOOC(CH2)5, Z = (CH2)11, X = Br] and III [R = n‐Bu, Z = (CH2CH2O)3CH2CH2, X = bis(trifluoromethylsulfonyl)imide (TFSI)]} are successfully utilized as initiators for ROP of CL, yielding corresponding polycaprolactones (PCL) Ia‐Br and IIIa‐TFSI. The oligoester II derived from I also acts as an initiator, providing block copolymer IIa‐Br. By anion exchange Ia‐Br and IIa‐Br are converted to Ia‐TFSI and IIa‐TFSI. The TFSI polymers have lower glass transition temperatures (Tg), resulting in higher conductivity, compared to the Br polymers. The ionic conductivities of the PCL block copolymers are higher than those of the PCL homopolymers, despite the similar Tg, because of their higher ionic content. Their static dielectric constants () increase linearly with ion content and exhibit the temperature dependence expected by Onsager, in the liquid state. The semi­crystalline PCL homopolymers, upon crystallization, undergo a significant increase in , owing to a Maxwell–Wagner–Sillars interfacial polarization. The present results demonstrate that with proper design, block copolymers have the potential to provide high ionic conductivities combined with good mechanical strength, key attributes for application of these materials in mechanical actuators. image