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

Abstract

The encoding of information by defining the sequence of monomers is a highly anticipated strategy for controlling the three-dimensional structures of polymers via information-driven chain folding and self-assembly. In this paper, we report the controlled chain folding of stereoblock poly­(lactic acid)­s (PLAs) composed of two oligo­(lactic acid) domains, [DLA n ] and [LLA n ], constructed by using precisely defined numbers of d- and l-lactic acids, respectively. Under the crystallization-driven self-assembly (CDSA) condition, block copolymers (BCPs) of stereoblock PLA and poly­(ethylene glycol) formed planar nanostructures having unilamellar crystalline cores of stereoblock PLA. [DLA n ]-[LLA n ] stereoblocks were folded predominantly by intramolecular stereocomplexation (SCN) in dilute solutions in which the intermolecular interaction between BCPs was suppressed. The thickness of the planar nanostructures was precisely defined by the number of repeating units constituted of [DLA n ] and [LLA n ] domains. The convergent synthesis of PLA permitted the addition of a single monomer unit between the [DLA n ] and [LLA n ] domains, resulting in the introduction of a desired functional group at the apex of the folded chain. Our results demonstrate that information encoded in the form of a monomer sequence may shape the polymer chain and guide its self-assembly toward specific nanostructures having the desired dimensions and functions.

Discrete Diblock Copolymers with Tailored Conformational Asymmetry: A Precise Model Platform to Explore Complex Spherical Phases

“…Discrete polymers with a uniform chain length and a precise chemical structure provide an ideal model system to resolve the phase behaviors with an unprecedentedly high resolution, validating the salient features captured by the theoretical computations. − A few discrete block copolymers have been developed and their phase behaviors have been scrutinized, unraveling intriguing details that have long been covered by molecular weight distribution. ,,− For example, a series of discrete diblock copolymers based on oligo dimethylsiloxane and oligo lactic acid were synthesized through an iterative growth approach by Meijer and co-workers, which self-organized into highly ordered cylinders, gyroids, and lamellae. ,, Johnson et al prepared a small library of stereoisomeric diblock copolymers, demonstrating that it is possible to regulate the self-assembly solely through rational stereochemical manipulations. ,, Our group recently constructed discrete giant polymeric chains using nanometer-sized monomers (i.e., molecular nanoparticles), highlighting the intriguing phase behaviors at a larger length scale. ,, Due to the synthetic challenges, however, the scope of discrete block copolymers and the diversity of the accessible phases are still rather limited . The stepwise synthetic approach can only be applied to certain monomers and is very difficult to reach a high degree of polymerization ( N ).…”

Seeded Epitaxial Growth of Crystallizable Polymers Governed by Crystallization Temperatures

“…Crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) with a crystallizable segment is a powerful tool used to create anisotropic polymer nanoparticles with precision control over size, shape, and compositions. − One-dimensional (1D) − and two-dimensional (2D) − precision polymer nanoparticles are extensively fabricated by using this approach. Living CDSA is a seeded growth approach of increasing importance for the creation of 1D/2D core–shell materials with enhanced complex structures from crystallizable BCPs. − In a seeded growth method, the crystallization process of nucleation and crystal growth is divided into two separated steps, i.e., the first step of preparation of crystalline seeds and the second step of crystal growth.…”

Discrete Diblock Copolymers with Precise Stereoconfiguration

“…Recently, Johnson and co-workers rationally designed a small library of discrete stereo- and sequence-defined diblock copolymers through iterative growth and demonstrated the possibility to regulate the molecular packing through stereochemical manipulations. − Hawker and co-workers prepared discrete isotactic and syndiotactic poly­(methyl methacrylate) by a combination of stereospecific polymerization techniques and automated flash chromatography purification . These elegant examples, among a few others, − have preliminarily revealed the indispensable contribution of stereochemistry that have long been blurred by chain length distribution. The potential of the chain chirality on rational structural engineering, however, has yet to be fully appreciated and exploited.…”