Combination of “living” nitroxide-mediated and photoiniferter-induced “grafting from” free-radical polymerizations: From branched copolymers to unimolecular micelles and microgels |
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Authors: | Daniel Gromadzki Sergey Filippov Ri?ardas Makuška Josef Pleštil Petr Št?pánek |
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Institution: | a Department of Supramolecular Polymer Systems, Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Square 2, 162 06 Prague 6, Czech Republic b Department of Polymer Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania |
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Abstract: | We report on solution properties of lightly grafted copolymers composed of polystyrene (PS) backbone (degree of polymerization of PS backbone, Nb=95) and variable length of poly(tert-butyl methacrylate) P(tBuMA) side chains (degree of polymerization of side chains, Nsc=14-222) at fixed number of grafting sites n = 11 and polydispersity index (Mw/Mn) ranging from 1.05 to 2.63. Synthesis of these graft copolymers is based on a novel synthetic route Gromadzki D, Makuška R, Netopilík M, Holler P, Lokaj J, Janata M, et al. Eur Polym J 2008;44:59-71] involving two independent controlled/“living” polymerization mechanisms, namely nitroxide-mediated radical polymerization (NMP) for the synthesis of the backbone and photoinduced “grafting from” iniferter process for building of P(tBuMA) branches. The viscosity-related contraction factors g′<1 confirmed high degree of branching of the studied graft copolymers. Dilute solutions of graft copolymers in non-selective solvent (THF), examined by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and viscometry, revealed a transition from comb-like conformation through wormlike-star to a microgel architecture under increasing number of monomeric units in side chains. These data were further supported by the structure factors Rη/Rh and Rg/Rh obtained by independent measurements and extrapolated to infinite dilution. Persistence lengths of the samples exhibiting comb-like topology were larger compared to linear polystyrene backbone and P(tBuMA) side chains in THF suggesting stiffening of the main chain with increasing size of the attached side chains. Unimolecular micelles were detected by DLS and SAXS in solvent selective for grafts, tert-amyl alcohol. |
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Keywords: | Controlled/&ldquo living&rdquo radical polymerization Branched copolymers Conformation Microgel Unimolecular micelles |
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