Preparation and characterization of poly(ethylene glycol)-block- poly[ε-(benzyloxycarbonyl)-l-lysine] thin films for biomedical applications

The nanoscale architectures evident in the thin films of self-assembling hybrid block copolymers - which are tailored to inherit the advantageous properties of their constituent synthetic (homo)polymer and polypeptide blocks - have continued to inspire a variety of new applications in different fields, including biomedicine. The thin films of symmetric hybrid block copolymer, α-methoxy-poly(ethylene glycol)-block-poly[ε-(benzyloxycarbonyl)-l- lysine], MPEG₁₁₂-b-PLL(Z)₁₇, were prepared by solvent casting in five different solvents and characterized using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy, Thermogravimetric analysis, Derivative Thermogravimetric analysis, Differential Scanning Calorimetry, Contact Angle goniometry, Wide-Angle X-ray Diffraction, and Scanning Electron Microscopy. Film thickness was estimated to be 51 ± 23 μm by the "step-height" method, using a thickness gauge. Although no significant change to the block copolymer's microstructure was observed, its solvent-cast films displayed divergent physical and thermal properties. The resulting cast films proved more thermally stable than the bulk but indicated greater block miscibility. Additionally, the thin films of MPEG₁₁₂-b-PLL(Z) ₁₇ preserved the microphase separation exhibited by the bulk copolymer albeit with appreciable loss of crystallinity. The surface properties of the polymer-air interface were diverse as were the effects of the casting solvents. Oriented equilibrium morphologies are also evident in some of the as-cast thin films.