Hybrid Polymers Bearing Mono/Oligo-L-Lysine(Z)s: ADMET Polymerization and Structural Investigations in the Solid State

Advancing novel polymers for biomedical applications requires in-depth knowledge between their chemical structure and physical properties under conditions such as assembly or folding. The secondary structure of hybrid-polymers containing lysine-residues (Lys) inside their main chain, separated by a stretch of n-alkyl-chains is here investigated. The polymer (A-[Lys_{n = 1}]_{m = 18}) is prepared by ADMET polymerization of the bis-ω-ene-functional mono-L-lysine(Z)s (Lys_{n = 1}) optimizing conditions for ADMET polymerization of Lys_{n = 1} monomers in bulk. The hybrid-polymers, A-[Lys_{n = 1}]_{m = 3, 7, 9, 18, 44} with molecular weights ranging from 1.3 to 17.6 kDa, display polydispersity (Đ) values in the range of 1.3–2.6. Comparison between these polymers and previously reported hybrid ADMET polymer, oligo-L-lysine(carboxybenzyl(Z)), (A-[Lys_n]_m) (i.e., n = 4, m = 24), containing longer stretches of the embedded lysine-unit was accomplished. Solid-state investigations (FT-IR and DSC) of the hybrid-polymers, A-[Lys_{n = 1}]_{m = 18}, A-[Lys_{n = 12}]_{m = 8,} and A-[Lys_{n = 24}]_{m = 4}, and the pre-polymers, Lys_{n = 12} and Lys_{n = 24} proved the presence of α-helices and β-folds at elevated temperatures in the range of 20 to 200 °C, further gaining understanding of the influence of the chain length of polymers on the formation of secondary structures.