Interpenetration network (IPN) assisted transcription of polymeric hollow spheres: A general approach towards composite hollow spheres Chengliang Zhang a , Shujiang Ding a , Jianjun Li a , Huifang Xu a , Lili Sun a , Wei Wei a , Cuiping Li a , Jiguang Liu a , Xiaozhong Qu a , Yunfeng Lu b , Zhenzhong Yang a, * a State Key Laboratory of Polymer Physics and Chemistry, Beijing National Laboratory of Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China b Department of Chemical and Biomolecular Engineering, University of California at Los Angeles, Los Angeles, CA 90095-1592, USA article info Article history: Received 14 February 2008 Received in revised form 10 April 2008 Accepted 30 April 2008 Available online 8 May 2008 Keywords: Interpenetration networks (IPN) Hollow spheres Composite abstract We have demonstrated a general and facile method to synthesize composite hollow spheres by IPN- assisted transcription of polymeric hollow spheres. Starting from a parent PS hollow sphere, IPN polymer composite hollow spheres have been synthesized by a swell polymerization within the shell. The shell thickness and the cavity size are tunable by altering the feeding amount of the monomers. A variety of functional groups are derived by a selective modification of one network of the IPN polymer composite hollow spheres. By specific interactions of desired materials with gels, composite hollow spheres are obtained. The composition of the shell can be controlled within polymer, carbon, inorganic, metal and metallic compounds, and their composites. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Hollow spheres, especially composite functional hollow spheres, have spurred increasing interests due to their diverse potential ap- plications such as drug delivery, artificial cells, biosensors, energy conversion and catalysis [1–3]. The key effects on applications are to control both structure and composition. Many methods have been developed to control morphology and composition, including layer- by-layer assisted deposition [4–7], graft onto a core template [8,9], and gel shell induced favorable growth [10]. These methods are es- sentially based on core–shell structure approach, which usually in- volves removal of the core templates. The resultant osmotic pressure will usually cause apertures or fragmentation in the shell. In order to avoid removal of the core templates, hollow vesicles or liposome have also been used as templates [11,12]. This method fails to form intact composite shells, due to a poor compatibility after the desired materials are incorporated within the weak thin shell. Emulsion or suspension polymerization has been employed to synthesize poly- mer hollow spheres [13–15], which also involves a removal of liquid cores. In addition, self-assembly of block copolymer [16–19], core- template-free synthesis [20,21], galvanic metal replacement [22], Kirkendall effect based method [23,24], and gas bubbles as soft- templates [25] are also proposed to prepare composite hollow spheres. These mentioned methods remain to be restricted within special compositions thus lacking generality. Herein, we present a facile approach to the synthesis of com- posite hollow spheres with an interpenetration network (IPN) shell. As illustrated in Fig. 1 , a commercial polystyrene (PS) hollow sphere A is selected as an example parent template [13]. Composition of the shell can be controlled along series sequential stages. (1) Hy- drophobic monomers B can swell the shell and sequentially poly- merize forming an A/B binary polymer IPN hollow sphere. In order to strengthen the IPN shell, crosslinkers are usually used together with the monomers. Phase separation during the polymerization is dynamically prohibited within the highly viscoelastic shell, ensur- ing a bicontinuous IPN structure. (2) Another functional network B1 with desired groups is further derived by a selective modification of desired one polymer network such as B within the composite shell. The physicochemical environment such as being charged and per- meable is thus tuned. (3) Desired materials can be favorably grown within network B1 by specific interactions resulting in another composite network B2, whose composition can be varied within polymers, inorganic materials, metals and their compounds. Along the similar procedure, another functional network A1 and com- posite network A2 can also be derived from the parent network A. 2. Experimental 2.1. Synthesis of IPN composite hollow spheres 2.1.1. PS/(crosslinked PAN) IPN hollow spheres In 100 mL of water, 5 g of freeze-dried powder of parent poly- styrene (PS) hollow spheres HP-433 (a Rohm & Haas product) with * Corresponding author. Fax: þ86 10 62559373. E-mail address: yangzz@iccas.ac.cn (Z. Yang). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2008.04.060 Polymer 49 (2008) 3098–3102