**2.7 Plasticization**

A number of attempts have been made on plasticized–polymer electrolytes in order to rise up the ionic conductivity greatly. Plasticization is generally recognized as one of the effective and efficient methods available for decreasing the crystalline region of polymer electrolytes (Suthanthiraraj et al., 2009). Plasticizer is a non–volatile and low molecular weight aprotic organic solvent which has a �� in the vicinity of –50 °C. Carbonate ester such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC) and

Characterization of High Molecular Weight Poly(vinyl chloride) –

the EC–based plasticized–polymer electrolytes (Ali et al., 2007).

**3. Materials** 

choosing the materials.

units of CH2–CHCl.

**3.1 Poly(vinyl chloride) PVC** 

Fig. 1. Chemical structure of PVC.

Lithium Tetraborate Electrolyte Plasticized by Propylene Carbonate 171

plasticizers, DOP was found to be the excellent plasticizer in term of thermal stability as proven in differential thermal analysis (DTA). The results show the reduced weight loss as increases the plasticizer concentration. Ali et al. (2007) studied the plasticized–polymer electrolytes that composed of PMMA, propylene carbonate (PC) or ethylene carbonate (EC) as plasticizer and LiTf or LiN(CF3SO2)2 as dopant salt. According to this literature, the ionic conductivity increases with the concentration of the plasticizer. They also declare that the PC–based plasticized–polymer electrolytes exhibit higher ionic conductivity compared to

Rajendran et al. (2004) also incorporated few types of plasticizers in the polymer electrolytes containing PVA/PMMA–LiBF4. The highest ionic conductivity of 1.29 mScm-1 had been observed for EC–based complex because of higher dielectric constant of EC (*ε*=85.1) (Rajendran et al., 2004). The addition of the plasticizer has been reported to reduce the crystallinity of the polymer complexes which in turns to a better ionic conductivity (Kelly et al., 1985). Kelly and co–workers assert that the presence of plasticizer exhibits downward shift in *Tg* due to the weaker interactions between the ions and polymer chain which in accordance with higher ion dissociation. A maximum electrical conductivity of 2.60×10−<sup>4</sup> Scm−1 at 300 K has been observed for 30wt.% of PEG as plasticizer compared to the pure PEO–NaClO4 system of 1.05×10−6 Scm−1. This can be explained that the addition of plasticizer enhances the amorphous phase in with concomitant the reduction in the energy barrier. Eventually, it results higher segmental motion of lithium ions (Kuila *et al*., 2007).

In this study, poly (vinyl chloride) (PVC), lithium tetraborate (Li2B4O7) and propylene carbonate (PC) were employed as host polymer, dopant salt and plasticizer, respectively. In this section, we discuss about the general description of the materials and the reasons for

Apart from PEO, poly(vinyl alcohol) (PVA), poly(acrylonitrile) (PAN), poly(ethyl methacrylate) (PEMA), poly(vinyl chloride) (PVC), poly(vinylidene fluoride) (PVdF) have also been used as polymer host materials. PVC is a thermoplastic polymer where its IUPAC name is poly(chloroethanediyl). It consists of numerous repeating units of monomers called vinyl chloride. It is a vinyl polymer composing of numerous repeating

C C C

n

H

H H H

H

Cl Cl

C

H

diethyl carbonate (DEC), and high dielectric constant solvent such as N,N– dimethylformamide (DMF), N,N–dimethylacetamide (DMAc) and *γ*–butyrolactone are widely used as main components of GPE (Pradhan et al., 2005; Suthanthiraraj et al., 2009; Ning et al., 2009). Other examples of common plasticizers are dibuthyl phthalate (DBP), diocthyl adipate (DOA) and polyethylene glycol (PEG) (Suthanthiraraj et al., 2009).
