Stereocomplexation of enantiomeric pairs of optically active polymers or between syndiotactic and isotactic polymers has led to improved thermal and mechanical properties of stereoregular polymer systems relative to the individual polymer components.  While stereocomplexation of polymer blends and stereoblock copolymers has been studied extensively with hydrophobic polymers, such as poly(lactic acid) (PLA) and poly(methyl methacrylate) (PMMA), functional amphiphilic polymer systems remain relatively unexplored, despite their essential roles in a number of advanced polymer applications, including therapeutic delivery, catalysis, and templating.  Anticipating that such interactions may impart interesting and potentially advantageous properties to amphiphilic block copolymer assemblies, this work explores the impact of stereocomplexation on nanostructures formed from amphiphilic block polypeptides.  The controlled stereochemistry and secondary structures characteristic of polypeptides render them an ideal platform for this study and provide added value for future application of these materials.  Sequential ring-opening polymerization of benzyl- and propargyl-substituted glutamate N-carboxyanhydrides produced well-defined functional block polypeptides, wherein the stereochemistry of the individual blocks was dictated by that of the monomer.  Modification of the alkyne groups of propargyl glutamate with hydrophilic thiols using photo-initiated thiol-yne click chemistry yielded amphiphilic polypeptides.  Nanostructures formed upon solution assembly of the amphiphilic stereoblock polypeptides were investigated using solid- and solution-state atomic force microscopy.  The optical and thermal properties of these polymers, evaluated by infrared and circular dichroism spectroscopies, thermogravimetric analysis, and differential scanning calorimetry, are also discussed.  Intertwining stereocomplexation interactions and amphiphilic block copolymer assembly is envisioned to have implications well beyond these fundamental studies to influence a wide range of nanostructure properties, including cargo release, secondary structure, and morphology, opening new opportunities for block copolymer nanostructures to enable a broad range of advanced applications.

Amphiphilic stereoblock polypeptides: Synthesis and solution assembly

254th National Meeting (2017)

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