Amphiphilic tadpole-shaped POSS-poly(glycerol methacrylate) hybrid polymers: synthesis and self-assembly

A new series of well-defined amphiphilic hybrid polymers of tadpole-shaped architecture with polyhedral oligomeric silsesquioxane (POSS) nanocage as the hydrophobic head and poly(glycerol methacrylate) (PGMA) as the hydrophilic tail (POSS-PGMA) has been synthesized via atom transfer radical polymerization (ATRP). The aminopropylIsobutyl POSS, a monofunctional POSS nanocage, was transformed into ATRP initiator by treating with 2-bromoisobutyrylbromide. The POSS-PGMA was achieved in two steps. First, solketal methacrylate (SMA) (the precursor monomer for GMA), synthesized by reacting solketal with methacryloyl chloride, was polymerized under typical ATRP conditions with THF as the solvent at 40 °C, employing the synthesized POSS based initiator, and CuCl/N,N,N,N,N-pentamethyldiethylenetriamine as the catalyst system. The size exclusion chromatography (SEC) chromatograms reveal monomodal molecular weight distributions and narrow polydispersity indices; suggesting that well-defined tadpole-shaped hybrid polymers have been achieved. This further confirms that the monofunctional POSS initiator is able to affectively polymerize SMA in a controlled fashion under ATRP conditions. In the second step, the obtained POSS-PSMA was transformed into amphiphilic POSS-PGMA by acid hydrolysis. The successful transformation could be verified by ¹H NMR and FTIR spectroscopy. Finally, because of the amphiphilic nature, the obtained POSS-PGMA could self-assemble when dispersed in water as confirmed by measuring the critical aggregation concentration (CAC) by fluorescence spectroscopy, using pyrene as the fluorescence probe. The CAC was found to increase with increasing the PGMA chain length. The large hydrodynamic size of the self-assembled structures, as determined by the laser light scattering data, however, suggests that the aggregates are not of typical core-shell type micelles.