Polyethers with phosphate pendant groups by monomer activated anionic ring opening polymerization: Syntheses, characterization and their lithium-ion conductivities Heeralal Vignesh Babu, Krishnamurthi Muralidharan * School of Chemistry, University of Hyderabad, Hyderabad 500 046, India article info Article history: Received 12 September 2013 Received in revised form 28 November 2013 Accepted 2 December 2013 Available online 10 December 2013 Keywords: Ring opening polymerization Lithium-ion conductivities Catalysis abstract This paper describes the preparations and lithium-ion conductivities of various solid polymer electro- lytes for potential use in high-energy density lithium-ion batteries. The ring opening polymerization of epoxides (M1eM6), catalyzed by Zn(II), Cu(II) and Cd(II) complexes in the presence of tetrabuty- lammonium bromide (TBAB), yielded polyethers (P1eP6) in which phosphates were attached as pendant groups. A reaction condition where Zn(II) catalyst used slightly excess to TBAB increased the polymeri- zation rate remarkably and yielded the polyethers with higher molar masses in a short time. These polymerizations proceeded following a “monomer activated anionic ring opening polymerization” mechanism. These living like polymerizations also progressed according to “formation of polymer chain per initiator” model. The solid-state lithium-ion conductivities of these polymers were examined using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The conductivity of one of the solid polymer elec- trolytes with 40 wt% of LiTFSI was 5.2  10 5 S cm 1 at room temperature and 2.9  10 4 S cm 1 at 80  C. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Several variations have been tried to increase the ionic con- ductivity of poly(ethylene oxide) (PEO) since its room temperature ionic conductivity is low (10 7 S cm 1 ) for practicable applications [1]. Some effective variations are; the PEO based composites pro- duced by mixing with polymer blends [2], inorganic fillers [3], plasticizers [4] and ionic liquids [5]; PEO based network polymers [6], cross-linked by siloxane polymers [7]; and block copolymers [8]. One of the major reasons causing the low ionic conductivity at ambient temperatures is the large crystalline area of PEO and less conformational flexibility. Therefore, there are interests towards decreasing crystallinity and increasing conformational flexibility. Since the amorphous region is responsible for the ion-conductivity, extending the amorphous phase can also improve the conductivity of polymers [9]. The ionic conductivity in amorphous polymers is caused by mobility of ions promoted by local segmental motion of the polymer chains above T g . Beyond T g , the polymer’s super- structures have disordered and flexible environment. Therefore, when the chains are in constant motion, vacant spaces would continually create and disappear through which ions can be transported. Because of the conformational flexibility induced by the presence of atoms of varying sizes in the polymer chains, the polyphosphazenes [10] and polysiloxanes [11] showed lithium ion conductivities of 5.0  10 5 S cm 1 and 4.5  10 4 S cm 1 respectively. Our interest is impelling conformational flexibilities and expanding the amorphous region; and examine the properties like crystallinity, T g and ionic conductivity of the polymer. Lithium-ion batteries are the major power sources for portable electronics. In the lithium-ion batteries, the electrodes are sepa- rated by an inert, porous polymer separator which is usually poly(propylene) soaked with low molecular weight organic liquids containing a dissolved salt. At room temperature, the ionic con- ductivity of liquid organic electrolytes is in the range of 10 3 S cm 1 . However, these organic liquids have potential fire hazard especially with large batteries that are useful for electric vehicles [12]. Thus, the research on finding solid polymer electrolyte (SPE) with flame- retardant properties to replace organic solvents in high-energy density lithium-ion batteries is always been in demand. The flame-retardant property for polymer electrolytes so far achieved by blending phosphorus containing molecules or covalently attaching them directly to the polymer chains [13]. Varieties of polymers in which phosphorus is a part of polymer chains are well- known [14e16]. However, the present interest is producing poly- ethers with bulky rigid pendant groups such as substituted phos- phates. These rigid groups would be influencing the assembly of * Corresponding author. Tel.: þ91 40 23012460. E-mail addresses: kmsc@uohyd.ernet.in, murali@uohyd.ac.in (K. Muralidharan). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymer.2013.12.005 Polymer 55 (2014) 83e94