Synthesis of Star Polymer by Atom Transfer Radical Polymerization with Resorcinol-Core Multifunctional Initiator: The Construction of Nanocapsule via Hydrolysis and Olefin Metathesis Reaction of the Obtained Star Polymer ATSUSHI NAGAI, TOSHIAKI HIRABAYASHI, HIROTO KUDO, TADATOMI NISHIKUBO Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1, Rokkakubashi, Kanagawa-Ku, Yokoyama 221-8686, Japan Received 29 August 2007; accepted 18 April 2008 DOI: 10.1002/pola.22824 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Olefin group-carrying styrene, 1-but-3-enyl-4-vinylbenznene (BVB), was polymerized via atom transfer radical polymerization (ATRP) initiated from C-meth- ylcalix [4]resorcinarene-based multifunctional initiator (CRA-bib) at low conversion to produce star polymer [poly(BVB)] with narrow molecular weight distribution (M w /M n < 1.35). The copolymerization of styrene (St) with poly(BVB) (M n ¼ 11,000, M w /M n ¼ 1.23) as a macroinitiator afforded star block copolymer [poly(BVB-b-St)] with M n ¼ 35,000 and M w /M n ¼ 1.44. The BVB layer of poly(BVB-b-St), located between the St shell and the CRA core, was crosslinked by olefin metathesis reaction of olefin groups o the BVB moieties. The removal of the CRA core of the crosslinked poly(BVB-b-St) by hydrolysis using KOH as a base gave polymeric hollow sphere [poly(cored crossBVB-b-St)] with good solubility in organic solvents. The morphological structure of the poly(cored crossBVB-b-St) showed spherical aggregates in THF by scanning electron microscopy (SEM). Furthermore, the nanocapsule structure of poly(cored crossBVB-b-St) with hollow spheres was found to be observed by transmission elec- tron microscopy (TEM). V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4879–4888, 2008 Keywords: atom transfer radical polymerization (ATRP); nanocapsule; spherical aggregate; star polymers; TEM INTRODUCTION Star polymers, consisting of one macromolecules possessing both one individual central branching core point and several polymeric arms, are of interest due to their unique properties, that is, a lower zero-shear viscosity and a decreased steady-state compliance in comparison with lin- ear polymers having similar molecular weights. 1,2 The synthesis of regular star polymers requires that a controlled and/or living polymerization technique be employed. Controlled radical poly- merizations (CRP) have proved to be versatile in the preparation of a multitude of star polymers. These methods include nitroxide-mediated poly- merization (NMP), reversible addition fragmenta- tion chain transfer (RAFT) polymerization, and atom transfer radical polymerization (ATRP). 3–5 ATRP 6–8 have been broadly applied to star poly- mer synthesis by using two approaches: (i) the arm-first 9–12 and (ii) the core-first methods. 13–15 The arm-first technique is crosslinking to the core after the linear arms of the star polymers Correspondence to: T. Nishikubo (E-mail: nishikubot@ kanagawa-u.ac.jp) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 46, 4879–4888 (2008) V V C 2008 Wiley Periodicals, Inc. 4879