Radiation Physics and Chemistry 74 (2005) 247–251 Effects of the degree of polymerization on the free volume structure of linear amphiphilic poly(isobutylene)–poly(methyl vinyl ether) diblock copolymers K. Su¨ vegh a,Ã , T. Marek b , A. Ve´ rtes b , Rudolf Faust c , Sa´ ndor Ke´ ki d , Miklo´s Nagy d , Miklo´ s Zsuga d a Department of Nuclear Chemistry, Eo¨tvo¨s Lora´nd University, PO Box 32, H-1518 Budapest 112, Hungary b Research Group for Nuclear Techniques in Structural Chemistry, HAS at Eo¨tvo¨s Lora´nd University, PO Box 32, H-1518 Budapest 112, Hungary c Polymer Science Program, Chemistry Department, University of Massachusetts Lowell, MA 01854, USA d Department of Applied Chemistry, University of Debrecen, H-4010 Debrecen, Hungary Abstract The free volume was studied in different poly(isobutylene)/poly(methyl vinyl ether) diblock copolymers by positron annihilation spectroscopy. The degree of polymerization of both constituents was varied in the work. The addition of further monomer units was found to increase the size of free volume holes continuously. However, the observed effect was much smaller than the size of monomer units. According to Doppler-broadening measurements, the structure of blocks changes with their size. r 2005 Elsevier Ltd. All rights reserved. 1. Introduction Block copolymers represent a special class of poly- mers in which each macromolecule is composed of two or more segments of homopolymers (called blocks) that are connected to each other. Based on the number of blocks, block copolymers can be classified as di-, tri- and multiblock copolymers. The arrangements of blocks can be linear, in which the blocks are simply connected via their ends, and star, in which all of the blocks are connected at a single junction. By an adequate choice of monomers and arrange- ments, a wide variety of block copolymers can be synthesized and a wide range of properties can be reached. Block copolymers are regularly used as stabilizers (Burguiere et al., 2001; Corcos et al., 1999; Ke´ki et al., 2000) and thermoplastic elastomers (Hiki et al., 2000; Sipos et al., 1995) and they are even used in exotic fields such as nano-scale lithography (Cheng et al., 2004; Rasmussen, 2004). Most applications of block copolymers are based on their so-called self-assembling properties. The different blocks—having totally different chemical properties— tend to form microphases in the bulk and exhibit micelle formation in an appropriate solvent or solvent mixture (Balsara et al., 1991; Raspaud et al., 1994; Tao et al., 1997; Ke´ki et al., 1998). In dilute aqueous solutions, above the critical micelle concentration (cmc), amphi- philic block copolymers, i.e., block copolymers consist- ing of hydrophobic and hydrophilic block segments, self-assemble into various aggregates of spherical micelles or vesicles (Alexandridis et al., 1996; Alexan- dridis and Hatton, 1995; Almgren et al., 1995; Yun ARTICLE IN PRESS www.elsevier.com/locate/radphyschem 0969-806X/$-see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2005.04.020 Ã Corresponding author. Fax: +3613722592. E-mail address: suveghk@para.chem.elte.hu (K. Su¨vegh).