Poly( N , N ‐dimethylacrylamide)‐ block ‐Poly( L ‐lysine) Hybrid Block Copolymers: Synthesis and Aqueous Solution Characterization

Four poly( N , N ‐dimethylacrylamide)‐ block ‐poly( L ‐lysine) (PDMAM‐ block ‐PLL) hybrid diblock copolymers and two PLL homo‐polypeptides are prepared via ROP of ε ‐trifluoroacetyl‐ L ‐lysine N ‐carboxyanhydride initiated by primary amino‐terminated PDMAM and n ‐hexylamine respectively. The PLL blocks render the copolymers a multi‐responsive behavior in aqueous solution due to their conformational transitions from random coil to α ‐helix with increasing pH, and from α ‐helix to β ‐sheet upon heating. The random coil‐to‐ α ‐helix transition is found to depend on the PLL length: the longer the peptide segment, the more readily the transition occurred. The same trend was observed for the α ‐helix‐to‐ β ‐sheet transition, which was found to be inhibited for short polypeptides unless conjugated with the PDMAM block.