Star-Like Polymers of tert-Butyl Acrylate via Controlled Radical Polymerization – Synthesis and Properties Andrzej Dworak, 1,2 Agnieszka Kowalczuk, 1 Barbara Mendrek, 1,2 Barbara Trzebicka * 1 Summary: Star polymers with different numbers and lengths of poly(tert-butyl acrylate) arms were obtained by the core-first method via atom transfer and iodine mediated radical polymerization. Multifunctional initiators with different numbers of initiating groups (from 3 to 28) were used to initiate the polymerization of tert-butyl acrylate, yielding stars with different numbers of arms. The structures of the stars were characterized by NMR and gel permeation chromatography with refractive index, multiangle laser light scattering and viscosimetric detectors. Keywords: branching parameters; controlled radical polymerization; core-shell polymers; poly(tert-butyl acrylate); star polymers Introduction Star polymers are branched structures consisting of a central core connected to linear chains. [1] The compact structure of stars is reflected in their solution and solid- state properties. For instance, stars have a lower hydrodynamic volume, smaller size and higher segment density than linear polymers of the same molar mass. [1,2] Well defined star structures are intensively investigated to determine the effect of the number of arms on the properties of polymers in solution and in the melt. Stars containing poly(tert-butyl acrylate) arms are especially interesting because pH sen- sitive covalently bonded spherical particles can be obtained after hydrolysis of the tert- butyl acrylate groups. [3–6] In general, three methods are commonly employed for the preparation of stars. [7] The arm-first method is based on the termination of living monofunctional poly- mer chains by a multifunctional terminating agent. In the core-first approach, a poly- functional core initiates monomer poly- merization, which forms the arms of the star. In the core-first approach, the number of arms in the star can be predefined, functional end groups can be easily intro- duced into the arms and unreacted linear chains are not observed if transfer reactions do not occur. Mixed, three step or in-out syntheses are a combination of arm-first and core-first methods that lead to well- defined miktoarm stars with chemically variable arms. [7] In the aforementioned methods, every step of the synthesis must be controlled, including the synthesis of the arms and the core, regardless of which structure is obtained first. To analyze the properties of stars, precise control of their architecture is required. Significant advancements in the field of controlled radical polymerization techniques have opened new routes to the synthesis of well-defined star structures by all three methods. [8–11] Non-linear polymers are characterized by determining the branching parameters, g and g 0 , [12,13] and the shape factor, r. [14–16] Macromol. Symp. 2011, 308, 93–100 DOI: 10.1002/masy.201151013 93 1 Centre of Polymer and Carbon Materials, Polish Academy of Sciences, M. Curie-Skl / odowskiej 34, 41-819 Zabrze, Poland E-mail: btrzebicka@cmpw-pan.edu.pl 2 University of Opole, Faculty of Chemistry, Oleska 48, 45-052 Opole, Poland Copyright ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com