Tailoring Micelle Formation and Gelation in (PEG−P(MA-POSS)) Amphiphilic Hybrid Block Copolymers

Abstract

We demonstrate that hydrophobic POSS (polyhedral oligomeric-silsesquioxane) nanoparticles, added to block copolymer solutions of poly(ethylene glycol) (PEG) and poly(methacrylisobutyl polyhedral oligomericsilsesquioxane) P(MA-POSS) as the hydrophilic and hydrophobic blocks respectively, could be employed to tailor their micelle formation, gelation, and rheological performance. For example, the hydrodynamic size of the micelles, formed by PEG5k-b-P(MA-POSS)3.6, increased from 13.6 ± 1.0 to 56.9 ± 3.7, an increase of more than four times, with 0.1 wt % (with respect to block copolymer) POSS nanoparticles in solution. However, the micelles retain their spherical morphology with core−shell structure as evidenced by calculating the values of dimensionless ratios, Rg/Rh for micelles as a function of added POSS nanoparticles content. For P(MA-POSS)-b-PEG10k-b-P(MA-POSS) triblock copolymers, which is associative in nature, addition of POSS nanoparticles resulted in formation of more robust and stronger hydrogels with a significantly higher storage modulus, G′, yield strengths, σy, and lower critical gelation concentration, cg, as compared with those for the pristine triblock copolymer. The presence of eight vinyl groups, attached to the POSS nanoparticles under investigations, is also exploited for further enhancement of rheological properties of the hydrogels with UV treatment. Finally, gel formation is induced in aqueous solutions of PEG5k-b-P(MA-POSS)3.6 diblock copolymer by introducing P(MA-POSS)-b-PEG10k-b-P(MA-POSS) triblock copolymer chains, and the rheological performance of the produced hydrogels, with certain compositions, is even superior to that of pure triblock copolymer gel.