Crystallization-Driven Self-Assembly of Block Copolymers Having Monodisperse Poly(lactic acid)s with Defined Stereochemical Sequences

Abstract

Monodisperse polymers composed of a discrete number of repeating units have attracted considerable interest as model systems to investigate the behavior of polymers having chemical structures without statistical distribution. Herein, we report the crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) built with monodisperse poly(lactic acid) (MPLA) composed of enantiomeric repeating units connected in a defined sequence and poly(ethylene glycol) (PEG). The morphology of self-assembled nanostructures was transformed by a systematic change in the number and the sequence of enantiomeric lactic acid units of MPLA blocks. This effect was more pronounced in the CDSA of a stereocomplex (SC) of a pair of BCPs having MPLA blocks configured in a complementary manner. When the size of the MPLA blocks was mismatched, a pair of the consequent BCPs self-assembled into nanostructures from nanoparticles to two-dimensional (2D) triangles and vesicles. In addition, on mismatching the stereochemical sequences of MPLA blocks forming the SC, the nanostructures of a BCP pair exhibited a transition from illdefined structures to 2D triangular structures. Our results suggest that the low-dimensional nanostructures created by the crystallization of MPLA-b-PEG could be manipulated by their precisely defined molecular weight and stereochemical sequences.

Crystallization‐Driven Controlled Two‐Dimensional (2D) Assemblies from Chromophore‐Appended Poly(L‐lactide)s: Highly Efficient Energy Transfer on a 2D Surface

“…The average thickness (≈12 nm) measured from atomic force microscopy (AFM) images (Figure 1b, S3) closely matched with that of the earlier reported PLLA single crystals with charged‐end groups [12c,d] . Previous studies have shown that monodisperse PLLA chains tend to form crystalline domain by chain folding at ≈32 repeat unit, which corresponds to a thickness of ≈10 nm [11d, 12k] . This suggests that the intrinsic CDSA features of the polymer remain unaffected by attachment of terminal chromophore and the MC‐functionalized 2D crystals were derived through single‐layer chain folded PLLA as reported earlier [12c,d,g,k] .…”

“…Previous studies have shown that monodisperse PLLA chains tend to form crystalline domain by chain folding at ≈32 repeat unit, which corresponds to a thickness of ≈10 nm [11d, 12k] . This suggests that the intrinsic CDSA features of the polymer remain unaffected by attachment of terminal chromophore and the MC‐functionalized 2D crystals were derived through single‐layer chain folded PLLA as reported earlier [12c,d,g,k] . Slightly greater thickness (≈12 nm) is attributed to the contribution from the MC units dangling on the surface.…”

Self-Assembly of Stereoblock Copolymers Driven by the Chain Folding of Discrete Poly(d-lactic acid-b-l-lactic acid) via Intramolecular Stereocomplexation

“…Initially, we investigated the CDSA of [DLA 16 ]-[LLA 16 ]- b -PEG in ethanol, conducted by dissolving the BCP in ethanol at 75 °C for 8 h, followed by cooling the reaction mixture to 25 °C at a rate of 0.2 °C/min. , The solution was equilibrated at 25 °C for 16 h and diluted with water, followed by 4 h of aging prior to analysis. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analyses of the CDSA result showed that at a concentration of 1 mg/mL in ethanol (0.226 μmol) [DLA 16 ]-[LLA 16 ]- b -PEG self-assembled into truncated triangular structures having protruding hairy peripheries (Figure a,c and Figure S3).…”

“…The folding of polymer chains is critical to their crystallization. , Stereoregular polymers such as poly­( l -lactic acid) (PLLA) and poly­( d -lactic acid) (PDLA) crystallize by the regular packing of folded segments of polymer chains. Therefore, the interval of intramolecular chain folding, measured by the number of repeating units, determines the thickness of the crystalline lamella formed by the packing of folded polymer domains. , For example, PLLA folds after every 32 repeating units in solution to form lamellar structures having a periodicity of ∼9 nm. − This lamellar thickness persists when the degree of polymerization of PLLA significantly exceeds the interval of chain folding …”

Discrete oligourethanes of sequence-regulated properties – impact of stereocontrol

“…11,12 Iterative macromolecule growth enables full control over monomer structure, their sequence, and stereochemistry. [13][14][15][16][17][18][19] However, the synthesis of sequence-defined polymers has many limitations in both cases. The use of solid support simplifies purification between steps but requires excesses of reagents and solvents.…”