Improvement in Comprehensive Properties of Poly(Methyl Methacrylate)-Based Gel Polymer Electrolyte by a Core-Shell Poly(Methyl Methacrylate)-Grafted Ordered Mesoporous Silica

Hindawi Publishing Corporation Journal of Nanomaterials Volume 2012, Article ID 457967, 10 pages doi:10.1155/2012/457967 Research Article Improvement in Comprehensive Properties of Poly(Methyl Methacrylate)-Based Gel Polymer Electrolyte by a Core-Shell Poly(Methyl Methacrylate)-Grafted Ordered Mesoporous Silica Lixin Xu, Feng Xu, Feng Chen, Jintao Yang, and Mingqiang Zhong College of Chemical Engineering and Materials Science, Zhejiang University of Technology, No. 18, Chaowang Road, 6th Zone, Chaohui, Hangzhou 310014, China Correspondence should be addressed to Mingqiang Zhong, Received 2 March 2011; Accepted 7 April 2011 Academic Editor: Sherine Obare Copyright © 2012 Lixin Xu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A novel strategy, herein, is demonstrated for improving comprehensive properties of poly (methyl methacrylate)(PMMA)-based gel polymer electrolyte (GPE) with a core-shell PMMA-grafted ordered mesoporous silica (OMS-g-PMMA). The OMS-g-PMMA was synthesized by surface-initiated atom transfer radical polymerization of methyl methacrylate from the exterior surface of OMS particle. A series of PMMA-based GPE membrances, filled with the OMS-g-PMMA of different contents, were further prepared by solution casting technique. The OMS-g-PMMA was confirmed to possess regular core-shell structure, in which a PMMA shell is chemically grafted to the exterior surface of silica core remaining intact mesoporous characteristics. Compared to the bare OMS, the OMS-g-PMMA is found to more effectively improve the comprehensive properties of PMMA-based GPE including ionic conductivity, thermal stability, and mechanical properties as well. For the PMMA-based GPE filled with 15 phr OMS-g-PMMA, the ionic conductivity at 25◦ C reaches 1.59 × 10−4 S · cm−1 , which is higher by nearly two orders than that of the corresponding filler-free parent GPE. Meanwhile, the tensile strength and Young’s modulus increase by 2.39 and 2.41 times, respectively, with an improvement in glass-transition temperature (Tg ) about 10◦ C. The excellent comprehensive properties make the PMMA-based GPE filled with OMS-g-PMMA as potential candidate for electrochemical devices. 1. Introduction Polymer electrolytes with excellent comprehensive properties have been attracting considerable attention in recent years with increasing demands for safe, lightweight lithium ion batteries, and various electrochemical devices of high performance. A great number of strategies, so far, have been explored for optimizing properties of polymer electrolytes, typically such as modification by adding plasticizers [1– 5], and inorganic fillers [6–10]. Among them, impregnating plasticizer into polymer matrix to form gel polymer electrolyte (GPE) is one of the widely adopted approaches, since GPE combines the advantages of liquid electrolytes with higher ionic conductivity and solid electrolytes without leakage [11]. Nevertheless, GPE usually exhibits poor mechanical properties and thermal instability owing to the existence of plasticizer, which is the major hindrance to their various practical applications. Although many methods have been successfully demonstrated for improving certain single property of GPE, it is still a challenge to develop GPE with excellent comprehensive performance including higher ionic conductivity, better mechanical properties and improved thermal stability as well. One of the preferable solutions to above challenge is to incorporate inorganic nanosized fillers, such as SiO2 [3, 7, 8], Al2 O3 [6, 12], TiO2 [6, 13], and layered clays [11], into GPE to form nanocomposite GPE (NGPE). It has been reported that the introduction of some inorganic nanosized fillers could lead to an improvement both in ionic conductivity and in other properties including mechanical strength and thermal stability [3, 11, 12]. The role of inorganic nanosized fillers in improving ionic conductivity of GPE is usually attributed to the Lewis acid-base interaction between the polar surface of fillers and ionic species, which yields more 2 mobile ion species, and thus leads to an improvement in ionic conductivity [14, 15]. In addition, some surface groups of inorganic nanosized fillers may provide physical crosslinking centers [16], and thus can improve, to an extent, the mechanical properties and thermal stability of GPE. Obviously, it is of great importance for NGPE to ensure a homogeneous dispersion of inorganic nanosized fillers in matrix for the above roles depend largely on the particle size and surface status of fillers. However, aggregation is usually inevitable in polymer matrix for the bare inorganic nanosized fillers due to their higher specific surface area and poor interfacial compatibilization with polymer matrix. Although the dispersibility of inorganic nanosized fillers in polymer matrix could be improved by surface modification with organic moieties such as coupling agent or polymer, the modified surface status of fillers usually leads to the dissociation of Lewis acid-base complex between the surface of fillers and ionic species, which is unfavorable to the improvement in properties of GPE. We herein explore a novel strategy for improving comprehensive properties of poly(methyl methacrylate) (PMMA)-based GPE by using a core-shell PMMA-grafted ordered mesoporous silica (OMS-g-PMMA) as filler. The OMS-g-PMMA possesses a PMMA shell, which is chemically grafted to the exterior surface of ordered mesoporous silica (OMS) as a core remaining intact mesoporous structure. The PMMA shell is expected to greatly improve the interfacial interaction between the OMS and PMMA matrix, and thus to impart the modified GPE with highly improved mechanical properties and thermal stability. Moreover, the silica core has ordered and tunable pore channels with larger surface area and abundant surface –OH, which is beneficial to the formation of Lewis acid-base interactions between fillers-ions and thus to the improvement in ionic conductivity of GPE. Although a large volume of research papers on application of OMS as fillers in composite polymer electrolyte (CPE) [10, 17–21] are available, researches related to the effect of core-shell polymer-grafted OMS hybrid particle as fillers in GPE are still scarce. In this research, the OMS-g-PMMA was synthesized by surface-initiated atom transfer radical polymerization (ATRP) of methyl methacrylate from the exterior surface of OMS particle and the PMMA-based GPE was prepared by solution casting technique using the OMS-g-PMMA as filler, LiClO4 as salt and propylene carbonate (PC) as plasticizer. The structure of the OMS-g-PMMA was characterized and the role of it in improving comprehensive properties of PMMA-based GPE was assessed. 2. Experimental Section 2.1. Materials. Propylene carbonate (PC, >99.5%) and 2-bromoisobut (...truncated)