Supramolecular Modification of ABC Triblock Terpolymers in Confinement Assembly

Abstract

The self-assembly of AB diblock copolymers in three-dimensional (3D) soft confinement of nanoemulsions has recently become an attractive bottom up route to prepare colloids with controlled inner morphologies. In that regard, ABC triblock terpolymers show a more complex morphological behavior and could thus give access to extensive libraries of multicompartment microparticles. However, knowledge about their self-assembly in confinement is very limited thus far. Here, we investigated the confinement assembly of polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or SVT) triblock terpolymers in nanoemulsion droplets. Depending on the block weight fractions, we found spherical microparticles with concentric lamella⁻sphere (ls) morphology, i.e., PS/PT lamella intercalated with P4VP spheres, or unusual conic microparticles with concentric lamella⁻cylinder (lc) morphology. We further described how these morphologies can be modified through supramolecular additives, such as hydrogen bond (HB) and halogen bond (XB) donors. We bound donors to the 4VP units and analyzed changes in the morphology depending on the binding strength and the length of the alkyl tail. The interaction with the weaker donors resulted in an increase in volume of the P4VP domains, which depends upon the molar fraction of the added donor. For donors with a high tendency of intermolecular packing, a visible change in the morphology was observed. This ultimately caused a shape change in the microparticle. Knowledge about how to control inner morphologies of multicompartment microparticles could lead to novel carbon supports for catalysis, nanoparticles with unprecedented topologies, and potentially, reversible shape changes by light actuation.

Keywords: 3D confinement assembly; block copolymers; halogen bond; microparticles; multicompartment; nanoemulsions; supramolecular chemistry.

Scheme 1

Formation of SVT multicompartment microparticles. (a) Chemical structure of polystyrene-b-poly(4-vinylpyridine)-b-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or SVT). (b) Solution of SVT in CHCl₃ followed by emulsification in water/CTAB, and evaporation of CHCl₃. (c) Solid microparticles of SVT with inner morphology, shown here with concentric lamella–sphere (ls) morphology. Inset shows arrangement of polymer chains.

Figure 1

TEM characterization of SVT1 and SVT2. (a) Overview image of spherical microparticles of SVT1 with ls morphology. The inset shows a close-up on one particle and a schematic explaining the distribution of phases. (b) TEM images of conic SVT2 with lc morphology. (c) The schematic shows the distribution of phases; the microparticle consists of PT/PS lamellae (green and grey) intercalated with the hexagonal packing of P4VP rings (blue). (Color code in TEM image: PS grey, P4VP dark grey due to iodine staining).

Scheme 2

Supramolecular complexation concept. (a) Chemical structure of employed XB and HB donors. (b) Tuning of the 4VP volume with XB and HB donors and transition from lamella–sphere (ls) to lamella–lamella (ll) morphology.

Figure 2

Microparticles made from SVT1/XB C8. (a) TEM of SVT1 with an increasing molar fraction of XB C8: (i) x = 0.25, (ii) x = 0.50, (iii) x = 0.75, (iv) x = 1.00. (Color code in TEM image: PS grey, P4VP dark grey due to iodine staining; scale bars are 100 nm). (b) Dependence of P4VP domain size on added XB C8. (c) IR spectra of SVT1 (black) and SVT1/XB C8 (x = 1.00, red).

Figure 3

Microparticles of SVT1 loaded with a molar fraction of bonders x = 1.00. TEM images of spherical microparticles with ls morphology obtained for (a) XB C8, (b) XB A8, (c) XB A12, (d) XB A16, (e) 8PAP, and (f) lauryl gallate (LG). Elliptic particles obtained for (g) cholesteryl hemisuccinate (CHEMS). (Color code in TEM image: PS grey, P4VP dark grey due to iodine staining).

Figure 4

Effect of supramolecular bonding on several length scales. (a) Binding of CHEMS causes uncoiling of P4VP and chain stretching of PS and PT. (b) On the mesoscale, the stretching results in flattened, lenticular P4VP domains. (c) Reorganization of the chains induces axially stacked PS/PT lamellae with shape change of the microparticle to prolate ellipsoids (color code in TEM image: PS grey, P4VP dark grey due to iodine staining).

Figure 5

Microparticles of SVT2 loaded with a molar fraction of bonders, x = 1.00. TEM images of conic microparticles with lc morphology obtained for (a) XB C8, (b) XB A8, (c) XB A16, (d) 8PAP, (e) LG, and (f) CHEMS. (Color code in TEM image: PS grey, P4VP dark grey due to iodine staining; scale bars are 200 nm).