Controlled synthesis of amino-acid based tadpole-shaped organic/inorganic hybrid polymers and their self-assembly in aqueous media.

Abstract

Synthesis, characterization and solution behavior of tadpole-shaped amphiphilic polymers with hydrophobic polyhedral oligomeric silsesquioxane (POSS) chain-end and hydrophilic main-chain having leucine pendants were investigated. Reversible addition-fragmentation chain transfer (RAFT) polymerization technique was employed to polymerize tert-butyloxycarbonyl-l-leucine methacryloyloxyethyl ester (Boc-Leu-HEMA) in the presence of POSS based RAFT agent. The POSS content and molecular weight of polymers could be controlled while maintaining a narrow molecular weight distribution (<1.3). Glass transition temperature (Tg) of tadpole shaped polymers (TSP) increased with increasing content of POSS moiety in the polymer matrix. Circular dichroism (CD) spectroscopy confirmed that the POSS moiety did not perturb the higher ordered secondary conformation of TSP, attained due to the presence of pendent chiral leucine moiety. Expulsion of side chain Boc groups produced pH responsive amphiphilic cationic polymers, which exhibited self-assembly in aqueous medium, confirmed by dynamic light scattering (DLS) and field-emission scanning electron microscopy (FE-SEM). The aggregation behavior of POSS end-capped polymeric nanoparticles was further investigated through nile red encapsulation as a hydrophobic probe in aqueous medium