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Imidazolium‐Based Ionic Liquids as Initiators in Ring Opening Polymerization: Ionic Conduction and Dielectric Response of End‐Functional Polycaprolactones and Their Block Copolymers
Author(s) -
Choi U Hyeok,
Mittal Anuj,
Price Terry L.,
Colby Ralph H.,
Gibson Harry W.
Publication year - 2016
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.201500424
Subject(s) - copolymer , ionic liquid , polymer chemistry , polymerization , ionic conductivity , glass transition , dielectric , imide , polymer , materials science , ring opening polymerization , monomer , ionic bonding , conductivity , chemistry , ion , organic chemistry , catalysis , composite material , electrolyte , optoelectronics , electrode
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(CH 2 ) 5 , Z = (CH 2 ) 11 , X = Br] and III [R = n‐ Bu, Z = (CH 2 CH 2 O) 3 CH 2 CH 2 , 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 ( T g ), 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 T g , because of their higher ionic content. Their static dielectric constants ( ε s ) 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 inε s , 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.