Nanosheets have in recent years received considerable attention because of their unique electronic and mechanical properties. They can be prepared by exfoliation of layered materials, but can also be formed via self-assembly which offers a much larger variability in size and chemical functionality. Self-assembly of amphiphilic molecules and polymers though usually leads to the formation of spherical, cylindrical and vesicular structures. The generation of nanosheets requires one to adjust the molecular structure such that planar bilayers sheets are formed with large bending constant to prevent closure into vesicles.

We report the formation of nanosheets or nanoplatelets from an amphiphilic block copolymer consisting of a poly(caprolactone) (PCL) and a fructose-functionalized poly(acrylate) (PFA) block (Scheme 1), prepared by RAFT-polymerization, in water. The nanoplatelets have a core/shell-structure, consisting of an inner core-sheet of the water-insoluble PCL-blocks and an outer sheet of the water-soluble PFA-blocks. The nanoplatelets are stabilized by the crystallization of the poly(caprolactone) block providing a sufficiently large bending constant. We use transmission electron microscopy (TEM) with phosphotungstic acid (PTA) negative staining to determine the thickness and lateral dimension of the nanoplatelets (Fig. 1). Using selected area electron diffraction (SAED) we prove the crystallinity of the poly(caprolactone) core-sheet (Fig. 2). The fructose-functionalized nanoplatelets have a thickness of 8 nm and lateral dimensions of 50 – 200 nm and are potential vectors for targeted drug delivery, where the planar geometry allows for large-area cooperative binding to cell surface receptors.

Figures:

Scheme 1: Structure of the block copolymer forming the nanoplatelets

Figure 1: TEM-image of self-assembled nanoplatelets showing their lateral dimension and thickness.

Figure 2: SAED-image of the nanoplatelets showing the crystallinity of the PCL-core sheet.

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EMC Abstracts - https://emc-proceedings.com/abstract/crystalline-nanoplatelets-of-a-pcl-fructose-block-copolymer/