Conformational and thermal analyses of α-methoxy-poly(ethylene glycol)-blockpoly[ε-(benzyloxycarbonyl)-L-lysine] hybrid block copolymers

Hybrid block copolymers find applications in drug delivery, tissue engineering, biomimetics and bioimaging, amongst others, mainly due to their propensity to form phase-separated microdomains as well as to the aggregation of their polypeptide segments. They not only enhance control over structure at the nanometre scale but also yield materials that can interface with various biosystems for different utilities. α-Methoxy-poly(ethylene glycol)-block-poly[ε-(benzyloxycarbonyl)-L-lysine] hybrid block copolymers of varying degrees of polymerization, MPEG_n-b-PLL(Z)_m, were synthesized by N-carboxyanhydride ringopening polymerization and characterized using infrared and NMR spectroscopy and gel permeation chromatography. Their secondary structures and bulk conformations were investigated using circular dichroism spectroscopy and wide-angle X-ray diffraction, respectively, whereas thermogravimetric analysis (TGA), derivative TGA and differential scanning calorimetry were employed for thermal analyses. The resulting block copolymers exhibited microphase separation and suppressed degrees of crystallinity with increasing L-lysine content and adopted α-helix and β-sheet secondary structures in aqueous milieu. The copolymers were also more thermally stable than their constituent homopolymers. Interestingly, the effects of the retention of the N^ε-benzyloxycarbonyl moiety on polymer properties proved considerable. The hybrid block copolymers herein afforded hierarchical structures of potential utility in the biomedical and pharmaceutical fields.