Macromolecular Nanotechnology Preparation and properties of polyimide/graphene oxide nanocomposite films with Mg ion crosslinker Jin-Yeon Kong a , Myeon-Cheon Choi a , Gwang Yeon Kim a , Jin Joo Park a , M. Selvaraj b , Mijeong Han c , Chang-Sik Ha a,⇑ a Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, Republic of Korea b School of Chemical and Biomolecular Engineering, Pusan National University, Busan 609-735, Republic of Korea c Advanced Materials Division, Korea Research Institute of Chemical Technology, 100 Jang-dong, Yuseong-gu, Daejeon 305-600, Republic of Korea article info Article history: Received 25 September 2011 Received in revised form 8 May 2012 Accepted 26 May 2012 Available online 15 June 2012 Keywords: Polyimide Graphene oxide Cross-linking Magnesium ions Properties abstract Polyimide(PI)/graphene oxide(GO) nanocomposite films were prepared by chemical cross- linking using small amounts of divalent Mg ions. The PI/GO nanocomposites showed enhanced tensile properties compared to pristine PI due to the presence of exfoliated GO in the PI matrix as well as crosslinking between poly(amic acid) (PAA), which is a precursor of PI, and GO by Mg ions. The hydrogen bonds between PAA and GO suppressed the phase separation between PI and GO, and small amounts of Mg ions can bond between the oxy- gen functional groups and carboxylate groups of GO and PAA. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Polymer-based composites were reported in the 1960s as a new paradigm for materials. High-performance lightweight composites could be developed and tailored to individual applications by dispersing strong and highly stiff fibres in a polymer matrix [1]. Polymer composites, particularly those containing conducting fillers, have been studied extensively over the past few decades because they can be utilized in elec- tromagnetic shielding, antistatic coatings, batteries, light emitting devices and other applications [2]. Among these con- ducting fillers, nanostructured carbon materials with graph- ene structures, such as carbon nanotubes (CNTs), carbon nanofibres (CNFs) and fullerenes, have been studied widely owing to their unique electric and micro- and macro- structural characteristics [3]. Graphene has attracted recent attention in material sciences owing to its unique structure of a two-dimensional sheet composed of sp 2 -bonded carbon atoms with a one-atomic thickness. Graphene has a high as- pect ratio (the ratio of lateral size to thickness), excellent elec- trical conductivity, and good tensile properties, which makes it an attractive candidate for use as an electronic and tensile filler. Furthermore, the presence of a paper-like structure may render graphene superior to CNTs for dispersion in a polymer matrix [4]. Among the known methods for creating graphene-based materials, graphene oxide (GO) by the oxida- tion of graphite is a versatile and easy processing method. GO has a wide range of oxygen functional groups on both the ba- sal planes and edges [5–8]. In addition, it can be simply exfo- liated and well-dispersed as graphene paper in both water and organic solvents for a range of applications in materials science including nanocomposites. Therefore, these materials have attracted attention as prominent hosts for hybrid mate- rials, particularly with a polymer matrix [4,9–18]. Aromatic polyimides (PIs) are well known high- performance polymeric materials owing to their good ten- sile properties, high-temperature durability, excellent chemical and thermal stabilities, low thermal expansion coefficient and low-dielectric constant [18–20]. Recently, 0014-3057/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eurpolymj.2012.05.015 ⇑ Corresponding author. Tel.: +82 51 510 2407; fax: +82 51 514 4331. E-mail addresses: csha@pusan.ac.kr, csha@pnu.edu (C.-S. Ha). European Polymer Journal 48 (2012) 1394–1405 Contents lists available at SciVerse ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj MACROMOLECULAR NANOTECHNOLOGY