Characterization of Polydimethylsiloxane- block-polystyrene (PDMS-b-PS) Copolymers by Liquid Chromatography at Critical Conditions Muhammad Imran Malik,* Pritish Sinha, Gareth M. Bayley, Peter E. Mallon, Harald Pasch Introduction Hybrid polymers are gaining increasing interest and applications in the field of polymer science and technology. These special materials allow quite different properties to be combined in one product and overcome some short- comings of pure materials. In addition, some specific properties can only be achieved by combining two or more blocks of distinctly different properties such as amphiphilic block copolymers which results in micelles in solvents where there is varying compatibilities to the two blocks. The applications of these hybrid materials in general have been described [1–7] and hybrid polymers containing poly- dimethylsiloxanes (PDMSs) in particular in ref. [8–11] Chen and co-workers [12–14] studied the surface segregation ability of di- and triblock copolymers as well as star polymers comprising of PDMS and polystyrene (PS). The different blocks of the hybrid materials under study have distinctly different properties, e.g., the glass transition temperature of PS is 100 8C (brittle solid at room tempera- ture) while that of PDMS is 127 8C (viscous liquid at room temperature even at higher molar masses), different surface energies, etc. Applications of PDMS hybrid polymers are found in the field of nanotechnology, electronics, filtration, and adsorption among many others. [8–21] Due to the incompatibility of the PS and PDMS blocks in the copolymer it is possible to control the phase segregation and the morphology at the nanoscale. The phase morphol- ogy is dictated by the composition and lengths of both blocks and the amount of unwanted homopolymer (PS or Full Paper Dr. M. I. Malik, Dr. P. Sinha, Dr. G. M. Bayley, Prof. P. E. Mallon, Prof. H. Pasch Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland7602, South Africa Fax: (þ27) 218084967; E-mail: imran@sun.ac.za In this study, liquid chromatography at critical conditions (LCCC) is used to determine the block lengths and molar masses of polydimethylsiloxane-block-polystyrene copolymers synthesized via atom transfer radical polymerization (ATRP) techniques. In addition, the analysis allows for the determination of the presence of homopoly- mers in the samples. LCCC at the critical point of polydimethylsiloxane (PDMS) on a reversed phase col- umn allows for the determination of PDMS homopo- lymer and the length of the polystyrene (PS) block in the block copolymer which elutes in the size exclusion chromatography (SEC) regime under these conditions. The PDMS block length and PS homopolymer can be obtained under normal phase conditions. The results of LCCC are compared with data from conventional SEC. Macromol. Chem. Phys. 2011, 212, 1221–1228 ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/macp.201000711 1221