|228. Plamper, F.A.; Becker, H.; Lanzendörfer, M.; Patel, M.; Wittemann, A.; Ballauff, M.; Müller, A.H.E.: Synthesis, Characterization and Aqueous Solution Behaviour of Star-shaped Poly(acrylic acid), Macromolecular Chemistry and Physics 206, 1813 (2005)|
We report the synthesis of star-shaped poly(tert-butyl acrylate) (PtBA) by atom transfer radical polymerization. We employ the core-first approach using glucose, saccharose and cyclodextrin based initiators leading to stars bearing five, eight and twenty one arms. Subsequent acidic treatment of PtBA leads to star-shaped poly(acrylic acid) (PAA). Alkaline cleavage of the arms enabled us to determine the initiation site efficiency. The PAA stars and arms were esterified to poly(methyl acrylate) (PMA). Molecular weight determination by means of GPC/viscosity, MALDI-ToF MS and NMR endgroup determination showed that initiation site efficiency is close to unity. Potentiometric titration of PAA arms and stars results increasing apparent pKa values with increasing arm number, which is a direct result of increasing segment density. Osmometry measurements of aqueous solutions of the PAA stars result in osmotic coefficients between 0.05 and 0.38, indicating that most of the counterions are confined within the star. The confinement increases with arm number.