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

Abstract

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.

Graphical abstract

Keywords:

• Block copolymer
• amino acid
• polyisobutylene (PIB)
• sequence-controlled polymer
• pH-responsive polymer

Acknowledgements

This work was supported by the Science and Engineering Research Board (SERB) [File No.: CRG/2021/000095], Government of India. A.D. acknowledges “Innovation in Science Pursuit for Inspired Research (INSPIRE),” Department of Science and Technology (DST), Government of India, for her Senior Research Fellowship (SRF).

Disclosure statement

The authors declare no competing financial interest.