Supramolecular self-assembly through inclusion complex formation between poly(ethylene oxide-b-N-isopropylacrylamide) block copolymer and a-cyclodextrin Cheng-Wei Tu a , Shiao-Wei Kuo b, ** , Feng-Chih Chang a, * a Institute of Applied Chemistry, National Chiao-Tung University, 30050 Hsinchu, Taiwan b Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung, Taiwan article info Article history: Received 6 February 2009 Received in revised form 20 April 2009 Accepted 21 April 2009 Available online 3 May 2009 Keywords: Cyclodextrin Inclusion complexes Block copolymer abstract A well-defined poly(ethylene oxide-block-N-isopropylacrylamide) (PEO-b-PNIPAM) diblock copolymer was synthesized by atom transfer radical polymerization and formed the inclusion complexes (ICs) after selective threading of the PEO segment of the block copolymer through the cavities of a-cyclodextrin (a-CD) units. The formation of the a-CD/PEO ICs between a-CD and PEO segment of the PEO-b-PNIPAM transformed the system from its original random coil conformation into a rod/coil-like structure. The stacking of the a-CD/PEO ICs and phase separation within the a-CD/PEO-b-PNIPAM IC resulted in the self- assembly of long-range-ordered lamellar structure exhibiting alternating layers of (i) a-CD/PEO ICs with hexagonally packed plates and (ii) amorphous phase of unincluded PEO/PNIPAM with brush conformation. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Supramolecular polymer chemistry has emerged as a fasci- nating subject within macromolecular research in recent years. A number of unique supramolecular architectures, such as poly- rotaxanes based on inclusion complexes (ICs) of cyclic host mate- rials and threaded guest molecules, have been reported as novel polymeric assemblies [1]. Cyclodextrins (CDs) have been the most popular host molecules employed to construct such molecular assemblies. CDs are cyclic oligosaccharides consisting of six (a), seven (b), or eight (g) glucose units linked by 1,4-a-glycosidic bonds [2]. They have a rigid, shallow truncated cone shape with a hydro- philic exterior and a hydrophobic interior cavity. The average diameters of the cavities of a-, b- and g-CD are 4.5, 7.0, and 8.5 Å, respectively, while the height of each CD’s torus is ca. 7.8 Å [3,4]. The cone-shaped cavities of CDs can act as hosts for a great variety of molecular guests [5]. The driving forces for IC formation are through a combination of geometric compatibility, van der Waals forces, and hydrophobic interactions between the CD cavity and the guest molecules [6,7]. Another important stabilizing force leads to the formation of ICs is hydrogen bonding between the hydroxyl groups situated along the rim of neighboring CDs [8,9]. Harada and Kamachi reported the first example of an IC formed via the self- assembly of a-CD and poly(ethylene glycol) [10]. Since this initial discovery of CD/polymer ICs, many other linear polymeric guests possessing either hydrophilic or hydrophobic properties have been reported to form ICs with various types of CDs [11–14]. Recently, a large number of publications have emerged describing the changes in the miscibility [15–17], crystallizability [18–20], and microdomain structures [21] of various polymers after formation of their respective CD ICs via selective threading onto guest segments. For example, a well-defined supramolecular structure for the a-CD ICs with linear poly(ethylene glycol) [22–24] and poly(3-capro- lactone) forms three-dimensional hexagonal crystal structures after reorganization through selective solvent treatment [22]. Zhu et al. have reported that the self-assembly process involves a gradual transition from an amorphous globule to a unique lamellar morphology consisting of stacked polypseudorotaxane bundles and amorphous polyether layers [25]. Although many guest polymers have been investigated for their interactions with various CDs, little attention has been paid to the changing morphologies of block copolymers after the formation of CD-based ICs. In a previous study, we found that the crystalline ICs formed from CDs and poly[(ethylene oxide)-ran-(propylene oxide)]-block-(g-benzyl-L-glutamate) [P(EO-r -PO)-b-PBLG] displays a bilayer-like structure possessing both hexagonally packed * Corresponding author. Tel./fax: þ886 3 5131512. ** Corresponding author. Fax: þ886 7 5254099. E-mail addresses: kuosw@faculty.nsysu.edu.tw (S.-W. Kuo), changfc@mail.nc- tu.edu.tw (F.-C. Chang). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2009.04.034 Polymer 50 (2009) 2958–2966