Multi-stimuli-responsive chiral-achiral ampholytic block copolymers composed of poly(N-acryloyl amino acid) and poly(vinyl amine)

Abstract

In this work, novel chiral-achiral ampholytic block copolymers comprising poly(N-acryloyl amino acid) and poly(vinyl amine), poly(VAm), were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization of N-acryloyl-L-glutamic acid (A-Glu-OH), which has two carboxylic acid moieties. The precursor of the cationic poly(VAm) segment, poly(NVPI), was prepared by the RAFT polymerization of N-vinylphthalimide (NVPI), which was employed as the macro-chain transfer agent (CTA). RAFT polymerization of A-Glu-OH in the presence of the dithiocarbamate-terminated poly(NVPI) macro-CTA and subsequent deprotection afforded ampholytic block copolymers with positive poly(VAm) and negative poly(A-Glu-OH) segments. For comparison, an ampholytic block copolymer with an amino acid-based polyelectrolyte having one carboxylic acid moiety in the monomer unit was prepared by the RAFT polymerization of N-acryloyl-L-alanine (A-Ala-OH). The resulting ampholytic block copolymers formed self-assembled micelles with electrostatically complexed cores and anionic shells, which were affected by pH values and salt and urea concentrations. In these micelles, interpolyelectrolyte complexes between the cationic poly(VAm) and anionic amino acid-based segment, corresponding to the core and chiral segment [poly(A-Glu-OH) or poly(A-Ala-OH)], respectively, contribute towards the manipulation of the multi-stimuli-responsive properties and functions of the shell. Selective interactions of DNA with the cationic poly(VAm) segment in the block copolymer were further investigated.