PIB-based block copolymer with a segment having alternating sequence of leucine and alanine side-chain pendants

A family of block copolymers with a hydrophobic polyisobutylene segment and another segment with an alternating sequence of tert-butoxy carbonyl (Boc)-leucine containing maleimide unit and Boc-alanine containing styrene unit was synthesized using a combination of living cationic and reversible addition-fragmentation chain transfer polymerizations. After successful deprotection of the Boc-groups from the pendant amino acids, the block copolymers become amphiphilic with free –NH3+ and –COOH functionalities in an alternating fashion in the poly(maleimide-alt-styrene) segment. The alternating sequence of leucine and alanine pendants throughout the second segment of the block copolymer chain was investigated systematically using NMR spectroscopy. In the pH range of 2–9, the deprotected copolymers showed pH-induced transformation of polymeric self-assemblies with critical aggregation concentrations ∼28 and ∼30 mg/L at pH 2 and pH 9, respectively. The pH-induced morphological transformation was well evidenced by 1H NMR spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy analysis. Additionally, these block copolymeric self-assemblies were studied for delivery applications at different pH, using Nile red as a model hydrophobic dye molecule.