Solution-grown composite single crystals of poly(L-lactic acid)-b-polystyrene block copolymers and poly(L-lactic acid) homopolymers

Focal Point Association of Core-Crystalline Micelles with an Amphiphilic Corona Block

We report the preparation of star-like supermicelles by the secondary association of triblock comicelles or scarf-like micelles driven by a change in solvency. These building blocks were synthesized by seeded growth in which crystallites of a triblock terpolymer, either PFS27-b-PTDMA81-b-POEGMA45 (to form triblock comicelles) or PFS66-b-PTDMA81-b-POEGMA45 (to form scarf-like micelles), served as seeds for crystallization-driven self-assembly (CDSA). PFS-b-PTDMA unimers were added in the seeded growth step. The corona-forming block PTDMA-POEGMA is amphiphilic and sensitive to polarity changes of the solvents. We sought solvents in which the upper critical solution temperature (UCST, TUCST) of POEGMA was slightly above room temperature (RT). Examples included 1-decanol and 1-decanol/decane mixtures. Seeded growth proceeded normally in solvents above the UCST of POEGMA. When the solution temperature was lowered below TUCST, or when the triblock comicelles or scarf-like micelles were transferred to a solvent (e.g., 1-decanol) below its TUCST, the center blocks associated to form star-like supermicelles. The addition of small amounts of THF to the medium to increase the solvency for POEGMA led to dissociation of the supermicelles. Transfer of the triblock comicelles to 1-pentanol at RT, below the UCST of PTDMA, also led to controlled secondary association to form supermicelles with a different morphology. Seeded growth with PFS25-b-PDMAEMA184 unimers led to supermicelles in which the poly(dimethylaminoethyl methacrylate) corona chains could serve as carriers for gold nanoparticles (AuNPs). These AuNP@supermicelle complexes could serve as recoverable catalysts, for example to catalyze the condensation polymerization of bis(dimethylsilyl)benzene and pentanediol. They were highly active catalysts and showed excellent mechanical robustness for recovery and reuse.

Shape-tunable two-dimensional assemblies from chromophore-conjugated crystallizable poly(L-lactides) with chain-length-dependent photophysical properties

This work reports temperature-dependent shape-changeable two-dimensional (2D) nanostructures by crystallization-driven self-assembly (CDSA) from a chromophore-conjugated poly(L-lactide) (PLLA) homopolymer (PTZ-P1) that contained a polar dye, phenothiazine (PTZ), at the chain-end of the crystallizable PLLA. The CDSA of PTZ-P1 in a polar solvent, isopropanol (iPrOH), by an uncontrolled heating-cooling process, majorly generates lozenge-shaped 2D platelets via chain-folding-mediated crystallization of the PLLA core, leading to the display of the phenothiazines on the 2D surface that confers colloidal stability and orange-emitting luminescent properties to the crystal lamellae. Isothermal crystallization at 60 °C causes a morphological change in PTZ-P1 platelets from lozenge to truncated-lozenge to perfect hexagon under different annealing times, while no shape change was noticed in the structurally similar PTZ-P2 polymer with a longer PLLA chain under similar conditions. This study unveils the complex link between the 2D platelet morphologies and degree of polymerization (DP) of PLLA and the corona-forming dye character. Further, the co-assembly potential of PTZ-P1 with hydrophobic pyrene-terminated PLLAs of varying chain lengths (PY-P1, PY-P2, and PY-P3) was examined, as these two dyes could form a Förster Resonance Energy Transfer (FRET) pair on the 2D surface. The impact of the length of the crystallizable PLLA on the photophysical properties of the surface-occupied chromophores revealed crucial insights into interchromophoric interactions on the platelet surface. A reduction in the propensity for π-stacking with increasing chain-folding in longer PLLAs is manifested in the chain-length-dependent FRET efficiencies and excimer emission lifetimes within the resultant monolayered 2D assemblies. The unconventional "butterfly-shaped" molecular architecture of the tested phenothiazine, combined with its varied functional features and polar character, adds a distinctive dimension to the underdeveloped field of CDSA of chromophore-conjugated poly(L-lactides), opening future avenues for the development of advanced nanostructured biodegradable 2D materials with programmable morphology and optical functions.

Nanoscale polymer discs, toroids and platelets: a survey of their syntheses and potential applications

Polymer self-assembly has become a reliable and versatile workhorse to produce polymeric nanomaterials. With appropriate polymer design and monomer selection, polymers can assemble into shapes and morphologies beyond well-studied spherical and cylindrical micellar structures. Steadfast access to anisotropic polymer nanoparticles has meant that the fabrication and application of 2D soft matter has received increasing attention in recent years. In this review, we focus on nanoscale polymer discs, toroids, and platelets: three morphologies that are often interrelated and made from similar starting materials or common intermediates. For each morphology, we illustrate design rules, and group and discuss commonly used self-assembly strategies. We further highlight polymer compositions, fundamental principles and self-assembly conditions that enable precision in bottom-up fabrication strategies. Finally, we summarise potential applications of such nanomaterials, especially in the context of biomedical research and template chemistry and elaborate on future endeavours in this space.

Uniform Two-Dimensional Crystalline Platelets with Tailored Compositions for pH Stimulus-Responsive Drug Release

Two-dimensional, size-tunable, water-dispersible particle micelles with spatially defined chemistries can be obtained by using "living" crystallization-driven self-assembly (CDSA) approach. Nevertheless, a major obstacle of crystalline particles in drug delivery application is the difficulty in accessing to cargo within crystalline cores. In the present work, we design four different types of biocompatible two-dimensional platelets with a crystalline poly(ε-caprolactone) (PCL) core, a hydrophobic poly(4-vinylprydine) (P4VP) segment, and a water dispersible poly(N,N-dimethyl acrylamide) (PDMA) block in ethanol by seeded growth method. Transferring those uniform platelets with tailored compositions to an aqueous solution in the presence of a hydrophobic drug leads to efficient encapsulation of the cargo in the P4VP segments via hydrophobic interactions. These drug-loaded platelets exhibit pH-responsive release behavior in aqueous media due to the protonated-deprotonated process of P4VP blocks in acidic and neutral solutions. This work provides initial insight into biocompatible PCL platelets with low dispersity and precise chemistry control in stimulus-responsive drug delivery fields.