Molecularly defined (L)-lactic acid oligomers and polymers: Synthesis and characterization

Sequence of Monomers and Position of Stereocenters Matter for Thermal Properties of Stereocontrolled Oligourethanes

Polyurethanes are commodity materials used for multiple applications. In recent years, a new category of polyurethane material has emerged, characterized by the lack of polymer molar mass dispersity, control of the monomer arrangement in the chain, and even full stereocontrol. Various multistep synthesis strategies have been developed to fabricate sequence-defined polyurethanes. However, synthesizing stereocontrolled polyurethanes with a controlled sequence is still a challenge. Polyurethanes with structural precision, as represented by biopolymers, i. e. proteins or nucleic acids, have opened new application directions for these groups of materials. It has been shown that polyurethanes can be used as biomimetics, information carriers, molecular tags, and materials with strictly controlled properties. Precise synthesis of macromolecules allows us to fine-tune the properties of polymers to specific needs. Therefore, it is essential to collect information on the sequence-structure relationship of polymers. In our work, we present synthetic pathways to make sequence and stereo-defined oligourethanes. We demonstrate that structural details, i. e., the monomer sequences and position of the stereocenter, have a tremendous effect on the thermal properties of model oligourethanes. We show that the introduction of chirality by constitutional isomerization can be used to program the thermal characteristics of polymers, which are key features for material applications.

Revealing the Effect of Stereocontrol on Intermolecular Interactions between Abiotic, Sequence-Defined Polyurethanes and a Ligand

The development of precision polymer synthesis has facilitated access to a diverse library of abiotic structures wherein chiral monomers are positioned at specific locations within macromolecular chains. These structures are anticipated to exhibit folding characteristics similar to those of biotic macromolecules and possess comparable functionalities. However, the extensive sequence space and numerous variables make selecting a sequence with the desired function challenging. Therefore, revealing sequence-function dependencies and developing practical tools are necessary to analyze their conformations and molecular interactions. In this study, we investigate the effect of stereochemistry, which dictates the spatial location of backbone and pendant groups, on the interaction between sequence-defined oligourethanes and bisphenol A ligands. Various methods are explored to analyze the receptor-like properties of model oligomers and the ligand. The accuracy of molecular dynamics simulations and experimental techniques is assessed to uncover the impact of discrete changes in stereochemical arrangements on the structures of the resulting complexes and their binding strengths. Detailed computational investigations providing atomistic details show that the formed complexes demonstrate significant structural diversity depending on the sequence of stereocenters, thus affecting the oligomer-ligand binding strength. Among the tested techniques, the fluorescence spectroscopy data, fitted to the Stern-Volmer equation, are consistently aligned with the calculations, thus validating the developed simulation methodology. The developed methodology opens a way to engineer the structure of sequence-defined oligomers with receptor-like functionality to explore their practical applications, e.g., as sensory materials.

Discrete Miktoarm Star Block Copolymers with Tailored Molecular Architecture

Molecular architecture is a critical factor in regulating phase behaviors of the block copolymer and prompting the formation of unconventional nanostructures. This work meticulously designed a library of isomeric miktoarm star polymers with an architectural evolution from the linear-branched block copolymer to the miktoarm star block copolymer and to the star-like block copolymer (i.e., 3AB → 3(AB1)B2 → 3(AB)). All of the polymers have precise chemical composition and uniform chain length, eliminating inherent molecular uncertainties such as chain length distribution or architectural defects. The self-assembly behaviors were systematically studied and compared. Gradually increasing the relative length of the branched B1 block regulates the ratio between the bridge and loop configuration and effectively releases packing frustration in the formation of the spherical or cylindrical structures, leading to a substantial deflection of phase boundaries. Complex structures, such as Frank-Kasper phases, were captured at a surprisingly higher volume fraction. Rationally regulating the molecular architecture offers rich possibilities to tune the packing symmetry of block copolymers.

Investigations into the characterization, degradation, and applications of biodegradable polymers by mass spectrometry

Biodegradable polymers have been getting more and more attention because of their contribution to the plastic pollution environmental issues and to move towards a circular economy. Nevertheless, biodegradable materials still exhibit various disadvantages restraining a widespread use in the market. Therefore, additional research efforts are required to improve their performance. Mass spectrometry (MS) affords a relevant contribution to optimize biodegradable polymer synthesis, to confirm macromolecular structures, to examine along the time the progress of degradation processes and highlight advantages and drawbacks in the extensive applications. This review aims to provide an overview of the MS investigations carried out to support the synthesis of biodegradable polymers, with helpful information on undesirable products or polymerization mechanism, to understand deterioration pathways by the structure of degradation products and to follow drug release and pharmacokinetic. Additionally, it summarizes MS studies addressed on environmental and health issues related to the extensive use of plastic materials, that is, potential migration of additives or microplastics identification and quantification. The paper is focused on the most significant studies relating to synthetic and microbial biodegradable polymers published in the last 15 years, not including agro-polymers such as proteins and polysaccharides.

Iridium-Catalyzed Synthesis of Chiral 1,2,3-Triazoles Units and Precise Construction of Stereocontrolled Oligomers

Iridium-catalyzed azide-thioalkyne cycloaddition reaction (IrAAC) has proved to be a powerful tool for the synthesis of fully substituted 1,2,3-triazole compounds with exclusive regioselectivity. Here we report its successful use in the precise construction of stereocontrolled oligomers that have great potential in diverse applications. Starting with the azide derived from L-prolinol and different functionalized thioalkynes, chiral 1,2,3-triazole units were fabricated with high efficiency under the IrAAC condition, which were further assembled into stereocontrolled oligotriazoles through metal-free exponential growth strategies. The structure and uniformity of these oligomers were well identified by ¹H NMR, size-exclusion chromatography, and mass spectrometry, the stereoregularity of which were studied through circular dichroism and circular polarized luminescence analysis.

Macromolecular Engineering: From Precise Macromolecular Inks to 3D Printed Microstructures

Macromolecules with complex, defined structures exist in nature but rarely is this degree of control afforded in synthetic macromolecules. Sequence-defined approaches provide a solution for precise control of the primary macromolecular structure. Despite a growing interest, very few examples for applications of sequence-defined macromolecules exist. In particular, the use of sequence-defined macromolecules as printable materials remains unexplored. Herein, the rational design of precise macromolecular inks for 3D microprinting is investigated for the first time. Specifically, three printable oligomers are synthesized, consisting of eight units, either crosslinkable (C) or non-functional (B) with varied sequence (BCBCBCBC, alternating; BBCCCBB, triblock; and BBBBCCCC, block). The oligomers are printed using two-photon laser printing and characterized. It is clearly demonstrated that the macromolecular sequence, specifically the positioning of the crosslinkable group, plays a critical role in both the printability and final properties of the printed material. Thus, through precise design and printability of sequence-defined macromolecules, an exciting avenue for the next generation of functional materials for 3D printing is created.

Thiophene End-Functionalized Oligo-(D,L-Lactide) as a New Electroactive Macromonomer for the "Hairy-Rod" Type Conjugated Polymers Synthesis

The development of the modern society imposes a fast-growing demand for new advanced functional polymer materials. To this aim, one of the most plausible current methodologies is the end-group functionalization of existing conventional polymers. If the end functional group is able to polymerize, this method enables the synthesis of a molecularly complex, grafted architecture that opens the access to a wider range of material properties, as well as tailoring the special functions required for certain applications. In this context, the present paper reports on α-thienyl-ω-hydroxyl-end-groups functionalized oligo-(D,L-lactide) (Th-PDLLA), which was designed to combine the polymerizability and photophysical properties of thiophene with the biocompatibility and biodegradability of poly-(D,L-lactide). Th-PDLLA was synthesized using the path of "functional initiator" in the ring-opening polymerization (ROP) of (D,L)-lactide, assisted by stannous 2-ethyl hexanoate (Sn(oct)₂). The results of NMR and FT-IR spectroscopic methods confirmed the Th-PDLLA's expected structure, while the oligomeric nature of Th-PDLLA, as resulting from the calculations based on ¹H-NMR data, is supported by the findings from gel permeation chromatography (GPC) and by the results of the thermal analyses. The behavior of Th-PDLLA in different organic solvents, evaluated by UV-vis and fluorescence spectroscopy, but also by dynamic light scattering (DLS), suggested the presence of colloidal supramolecular structures, underlining the nature of the macromonomer Th-PDLLA as an "shape amphiphile". To test its functionality, the ability of Th-PDLLA to work as a building block for the synthesis of molecular composites was demonstrated by photoinduced oxidative homopolymerization in the presence of diphenyliodonium salt (DPI). The occurrence of a polymerization process, with the formation of a thiophene-conjugated oligomeric main chain grafted with oligomeric PDLLA, was proven, in addition to the visual changes, by the results of GPC, ¹H-NMR, FT-IR, UV-vis and fluorescence measurements.

Effect of Molecular Architecture and Symmetry on Self-Assembly: A Quantitative Revisit Using Discrete ABA Triblock Copolymers

The inherent statistical heterogeneities associated with chain length, composition, and architecture of synthetic block copolymers compromise the quantitative interpretation of their self-assembly process. This study scrutinizes the contribution of molecular architecture on phase behaviors using discrete ABA triblock copolymers with precise chemical structure and uniform chain length. A group of discrete triblock copolymers with varying composition and symmetry were modularly synthesized through a combination of iterative growth methods and efficient coupling reactions. The symmetric ABA triblock copolymers self-assemble into long-range ordered structures with expanded domain spacings and enhanced phase stability, compared with the diblock counterparts snipped at the middle point. By tuning the relative chain length of two end blocks, the molecular asymmetry reduces the packing frustration, and thus increases the order-to-disorder transition temperature and enlarges the domain sizes. This study would serve as a quantitative model system to correlate the experimental observations with the theoretical assessments and to provide quantitative understandings for the relationship between molecular architecture and self-assembly.

Diazido macrocyclic sulfates as a platform for the synthesis of sequence-defined polymers for antibody drug conjugates

To improve the efficacy of antibody drug conjugates (ADCs), there has been significant focus on increasing the drug-to-antibody ratio (DAR) in order to deliver more payload. However, due to the hydrophobicity of many cytotoxics, highly-loaded conjugates often have lower physicochemical stability and poorer pharmacokinetic outcomes, requiring the development of new hydrophilic linkers. Herein, we report a platform for the preparation of functional, sequence-defined polymers for conjugation to antibodies. We demonstrate the successful synthesis of novel diazido macrocyclic sulfate monomers of varied size ranging from 4 to 7 ethylene glycol repeat units. These monomers were then successively ring-opened to produce sequence-defined polymers that contained either 4 or 6 azides for post-synthesis functionalization. Given the hydrophilic ethylene glycol backbone and chemically defined nature of the polymers, we envisioned this as a useful strategy in the preparation of highly-loaded ADCs. To demonstrate this, we prepared a model polymer-fluorophore scaffold composed of 4 coumarin molecules and conjugated it to Herceptin. We fully characterized the conjugate via mass spectrometry, which yielded a polymer-to-antibody ratio of 6.6, translating to a total of 26 fluorophores conjugated to the antibody at the inter-chain disulfides. We believe this technology to not only be a meaningful contribution to the field of sequence-defined polymers and conjugates, but also as a general and tunable platform for drug delivery.

Discrete oligourethanes of sequence-regulated properties – impact of stereocontrol

Properties and functions of natural biopolymers such as proteins are strongly dependent on the sequence of amino acid monomers. The regulation of the properties of synthetic polymers by controlling monomer...

Synthesis of discrete bottlebrush polymers via the iterative convergent growth technique and post-functionalization

The formation of discrete bottlebrush polymers (Step 1: Iterative convergent growth. Step 2: Post-functionalization using thiol–ene click chemistry.)

Precisely Encoding Geometric Features into Discrete Linear Polymer Chains for Robust Structural Engineering

Molecular shape is an essential parameter that regulates the self-organization and recognition process, which has not yet been well appreciated and exploited in block polymers due to the lack of precise and efficient modulation methods. This work (i) develops a robust approach to break the intrinsic symmetry of linear polymers by introducing geometric features into otherwise homogeneous chains and (ii) quantitatively highlights the critical contribution of molecular geometry/architecture to the self-assembly behaviors. Iteratively connecting homologous monomers of different side chains according to pre-designed sequences generates discrete polymers with exact chemical structure, uniform chain length, and programmable side-chain gradient along the backbone, which transcribes into diverse shapes. The precise chemistry eliminates all the defects and heterogeneities, providing a delicate platform for fundamental inquiries into the role of molecular geometry. A rich collection of unconventional complex phases, including Frank-Kasper A15 and σ phases, as well as a dodecagonal quasicrystal phase, were captured in these rigorous single-component systems. The self-assembly behaviors are strikingly sensitive to subtle variations of geometry, such that simply migrating a few methylene units among the side chains would generate substantial differences in lattice size or phase stability, or even trigger a phase transition toward distinct structures. The phenomena can be rationalized with a geometric argument that nonuniform side chain distribution leads to conformational mismatch between two immiscible blocks, resulting in varied interfacial curvatures and distinct lattice symmetries. The profound contribution demonstrates that molecular geometry is an effective and robust parameter for structural engineering.

Hierarchical Nanomaterials Assembled from Peptoids and Other Sequence-Defined Synthetic Polymers

In nature, the self-assembly of sequence-specific biopolymers into hierarchical structures plays an essential role in the construction of functional biomaterials. To develop synthetic materials that can mimic and surpass the function of these natural counterparts, various sequence-defined bio- and biomimetic polymers have been developed and exploited as building blocks for hierarchical self-assembly. This review summarizes the recent advances in the molecular self-assembly of hierarchical nanomaterials based on peptoids (or poly-N-substituted glycines) and other sequence-defined synthetic polymers. Modern techniques to monitor the assembly mechanisms and characterize the physicochemical properties of these self-assembly systems are highlighted. In addition, discussions about their potential applications in biomedical sciences and renewable energy are also included. This review aims to highlight essential features of sequence-defined synthetic polymers (e.g., high stability and protein-like high-information content) and how these unique features enable the construction of robust biomimetic functional materials with high programmability and predictability, with an emphasis on peptoids and their self-assembled nanomaterials.

Crystallization Induced Self-Assembly: A Strategy to Achieve Ultra-Small Domain Sizes

Achieving self-assembled nanostructures with ultra-small feature sizes (e. g., below 5 nm) is an important prerequisite for the development of block copolymer lithography. In this work, the preparation and self-assembly of a series of giant molecules composed of vinyl polyhedral oligomeric silsesquioxane (VPOSS) tethered with monodispersed oligo(L-lactide) chains are presented. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) results demonstrate that ultra-small domain sizes (down to 3 nm) of phase separated lamellar morphology are achieved in bulk, driven by the strong tendency and fast kinetics for crystallization of VPOSS moieties. Moreover, upon gamma ray radiation, VPOSS cages in the lamellar structure can be crosslinked via polymerization of the vinyl groups. After pyrolysis at high temperature, ultra-thin two-dimensional nano-silica sheets can be obtained.

Downsizing of Block Polymer-Templated Nanopores to One Nanometer via Hyper-Cross-Linking of High χ-Low N Precursors

Synthesizing nanoporous polymer from the block polymer template by selective removal of the sacrificial domain offers straightforward pore size control as a function of the degree of polymerization (N). Downscaling pore size into the microporous regime (<2 nm) has been thermodynamically challenging, because the low N drives the system to disorder and the small-sized pore is prone to collapse. Herein, we report that maximizing cross-linking density of a block polymer precursor with an increased interaction parameter (χ) can help successfully stabilize the structure bearing pore sizes of 1.1 nm. We adopt polymerization-induced microphase separation (PIMS) combined with hyper-cross-linking as a strategy for the preparation of the bicontinuous block polymer precursors with a densely cross-linked framework by copolymerization of vinylbenzyl chloride with divinylbenzene and also Friedel-Crafts alkylation. Incorporating 4-vinylbiphenyl as a higher-χ comonomer to the sacrificial polylactide (PLA) block and optimizing the segregation strength versus cross-linking density allow for further downscaling. Control of pore size by N of PLA is demonstrated in the range of 9.9-1.1 nm. Accessible surface area to fluorescein-tagged dextrans is regulated by the relative size of the pore to the guest, and pore size is controlled. These findings will be useful for designing microporous polymers with tailored pore size for advanced catalytic and separation applications.

Applications of Discrete Synthetic Macromolecules in Life and Materials Science: Recent and Future Trends

In the last decade, the field of sequence-defined polymers and related ultraprecise, monodisperse synthetic macromolecules has grown exponentially. In the early stage, mainly articles or reviews dedicated to the development of synthetic routes toward their preparation have been published. Nowadays, those synthetic methodologies, combined with the elucidation of the structure-property relationships, allow envisioning many promising applications. Consequently, in the past 3 years, application-oriented papers based on discrete synthetic macromolecules emerged. Hence, material science applications such as macromolecular data storage and encryption, self-assembly of discrete structures and foldamers have been the object of many fascinating studies. Moreover, in the area of life sciences, such structures have also been the focus of numerous research studies. Here, it is aimed to highlight these recent applications and to give the reader a critical overview of the future trends in this area of research.

Discrete Block Copolymers with Diverse Architectures: Resolving Complex Spherical Phases with One Monomer Resolution

This work describes the first rigorous example of a single-component block copolymer system forming unconventional spherical phases. A library of discrete block polymers with uniform chain length and diverse architectures were modularly prepared through a combination of a step-growth approach and highly efficient coupling reactions. The precise chemical structure eliminates all the molecular defects associated with molar weight, dispersity, and compositional ratio. Complex spherical phases, including the Frank-Kasper phase (A15 and σ) and quasicrystalline phase, were experimentally captured by meticulously tuning the composition and architectures. A phase portrait with unprecedented accuracy was mapped out (up to one monomer resolution), unraveling intriguing details of phase behaviors that have long been compromised by inherent molecular weight distribution. This study serves as a delicate model system to bridge the existing gaps between experimental observations and theoretical assessments and to provide insights into the formation and evolution of the unconventional spherical phases in soft matter systems.

Architecture-Dependent Interplay between Self-Assembly and Crystallization in Discrete Block Co-Oligomers

Access to versatile and stable nanostructures formed by the self-assembly of block copolymers in water is essential for biomedical applications. These applications require control over the stability, morphology, and size of the formed nanostructures. Here, we study the self-assembly in water of a library of fully discrete and sequence-controlled AB-type block co-oligomers (BCOs) of oligo(l-lactic acid)-b-oligo(ethylene glycol). In this series, we eliminate all the inherent uncertainty associated with molar mass, ratio, and compositional dispersity, but vary the ratio between the water-soluble and water-insoluble parts. The BCO library is designed in such a way that vesicles, spherical micelles, and cylindrical micelles are generated in solution, hereby covering a variety of common morphologies. With the help of self-consistent field (SCF) computations, the thermodynamic structures in water are predicted for all structures. The morphologies formed were experimentally analyzed using a combination of calorimetry and scattering techniques. When comparing the experimentally found structures with those predicted, we find an excellent agreement. Intriguingly, calorimetry showed the presence of crystallized l-lactic acid (LLA) units in the bilayer of the lamellar forming BCO. Despite this crystallinity, there is no mismatch between the predicted and observed bilayer thicknesses upon self-assembly in water. In this case, phase separation driven by the hydrophobic LLA block coincides with crystallization, resulting in stable morphologies. Thus, SCF guided library design and sample preparation can lead toward robust formulations of nanoparticles.

Sequence-defined l-glutamamide oligomers with pendant supramolecular motifs via iterative synthesis and orthogonal post-functionalization

One of the great challenges in polymer chemistry is to achieve discrete and sequence-defined synthetic polymers that fold in defined conformations and form well-defined three-dimensional structured particles.

Easily readable palindromic sequence-defined polymers built by cascade thiol-maleimide Michael couplings

The rational combination of cascade thiol-maleimide Michael couplings (CTMMC) with iterative exponential chain growth was demonstrated as an efficient way to synthesize palindromic sequence-defined polymers.

Stereocontrolled, multi-functional sequence-defined oligomers through automated synthesis

In this work, stereocontrolled sequence-defined oligomers were prepared using an automated thiolactone-based platform that allows post-synthesis functionalisation.

Effects of crystallinity and dispersity on the self-assembly behavior of block co-oligomers in water

Dispersity and crystallinity affect the dimensions of lamellar structures formed by amphiphilic block co-oligomers in water as well as the reproducibility of sample formation; spherical and cylindrical morphologies are less affected.

Precise modulation of molecular weight distribution for structural engineering

As one of the most critical molecular parameters, molecular weight distribution has a profound impact on the structure and properties of polymers. Quantitative and comprehensive understanding, however, has yet to be established, mainly due to the challenge in the precise control and regulation of molecular weight distribution. In this work, we demonstrated a robust and effective approach to artificially engineer the molecular weight distribution through precise recombination of discrete macromolecules. The width, symmetry, and other characteristics of the distribution can be independently manipulated to achieve absolute control, serving as a model platform for highlighting the importance of chain length heterogeneity in structural engineering. Different from their discrete counterparts, each individual component in dispersed samples experiences a varied degree of supercooling at a specific crystallization temperature. Non-uniform crystal nucleation and growth kinetics lead to distinct molecular arrangements. This work could bridge the gap between discrete and dispersed macromolecules, providing fundamental perspectives on the critical role of molecular weight distribution.

Exploring with Molecular Dynamics the Structural Fate of PLGA Oligomers in Various Solvents

This study focuses on the solvent effects that promote preferred solvated structures of polylactic-co-glycolic acid (PLGA) oligomers of molecular weight 278, 668, and 1449 u in ethyl acetate, water, and a mixture of both solvents. Our methodology consists of all-atom, explicit solvent molecular dynamics simulations for inspection of the solvated oligomer structures at ambient conditions. Parameters for the generalized Amber force field are developed in this work for the ethyl acetate liquid and the PLGA oligomers. Energetics, oligomer radius of gyration, end-to-end distance, orientational order parameter, flexibility coefficient, and backbone dihedral angles are reported along with a size scaling property yielding a power law for PLGA oligomers in each of the three solvents considered. It is found that the PLGA oligomer has two characteristic states identified by a set of extended structures and a set of collapsed structures, the former being energetically preferred in ethyl acetate and its mixture with water. The two types of PLGA structures occur in the three solvents and although they flip from one to the other in a sporadic fashion, in ethyl acetate, the extended structures may persist for more than 20 ns. The collapsed structures are significantly more frequent in water, occurring seldom in the mixed ethyl acetate-water solvent. PLGA is a biodegradable polymer approved for use in pharmaceutical and biomedical applications. Insights provided therein are of importance for the polymer aggregation process and its glassy state in condensed phases.

About the Crystallization of Abiotic Coded Matter

The crystallization of digitally encoded polyurethanes was studied by electron diffraction. A series of oligomers with different primary structures was analyzed in this work. They all form hydrogen-bonding-directed lamellar single crystals with a base-centered orthorhombic unit cell. Although crystal morphology was the same in all cases, the digital coding of the oligomers has a small influence on the intersheet distance in the crystals. The crystal lattices allow calculation of the volume occupied by one basic information unit, which is in the range 148-188 ų. Interestingly, this volume is about 3× smaller than that occupied by a coded nucleotide in a DNA double helix. Furthermore, crystallization of blends of oligourethanes with different coded primary structures was investigated. Oligomers with drastically different monomer compositions form structures that are not cocrystals but more probably segregated crystals containing distinct domains of different composition.

Oligo(Lactic Acid)8-Rapamycin Prodrug-Loaded Poly(Ethylene Glycol)-block-Poly(Lactic Acid) Micelles for Injection

PURPOSE

To prepare an oligo(lactic acid)₈-rapamycin prodrug (o(LA)₈-RAP)-loaded poly(ethylene glycol)-block-poly(lactic acid) (PEG-b-PLA) micelle for injection and characterize its compatibility and performance versus a RAP-loaded PEG-b-PLA micelle for injection in vitro and in vivo.

METHODS

Monodisperse o(LA)₈ was coupled on RAP at the C-40 via DCC/DMAP chemistry, and conversion of o(LA)₈-RAP prodrug into RAP was characterized in vitro. Physicochemical properties of o(LA)₈-RAP- and RAP-loaded PEG-b-PLA micelles and their antitumor efficacies in a syngeneic 4 T1 breast tumor model were compared.

RESULTS

Synthesis of o(LA)₈-RAP prodrug was confirmed by ¹H NMR and mass spectroscopy. The o(LA)₈-RAP prodrug underwent conversion in PBS and rat plasma by backbiting and esterase-mediated cleavage, respectively. O(LA)₈-RAP-loaded PEG-b-PLA micelles increased water solubility of RAP equivalent to 3.3 mg/ml with no signs of precipitation. Further, o(LA)₈-RAP was released more slowly than RAP from PEG-b-PLA micelles. With added physical stability, o(LA)₈-RAP-loaded PEG-b-PLA micelles significantly inhibited tumor growth relative to RAP-loaded PEG-b-PLA micelles in 4 T1 breast tumor-bearing mice without signs of acute toxicity.

CONCLUSIONS

An o(LA)₈-RAP-loaded PEG-b-PLA micelle for injection is more stable than a RAP-loaded PEG-b-PLA micelle for injection, and o(LA)₈-RAP converts into RAP rapidly in rat plasma (t_1/2 = 1 h), resulting in antitumor efficacy in a syngeneic 4 T1 breast tumor model.

Scalable Synthesis of Positively Charged Sequence-Defined Functional Polymers

Synthesizing and characterizing sequence-defined polymers with positively charged backbone are great challenges. By alternately processing Menschutkin reaction and Cu-catalyzed azide-alkyne cycloaddition reaction, we successfully synthesized series of scalable cationic sequence-defined polymers with quaternary ammonium backbone up to 12 repeating units and characterized their precise structures. Due to the dramatic polarity difference between weak polar feed molecules and strong polar target molecules, simple precipitation in weak polar solvents is enough to obtain pure sequence-defined polymers. Such a polar-inverse strategy (PIS), without protecting groups and solid support, offers extremely high yields up to 68% after 12 reaction steps (i.e., average yield >95% for each step), favoring cost-effective large-scale production. Because of the independent reactivity of selected functional groups, the cationic sequence-defined polymers are highly programmable, including backbone composition, sequence order, functional side groups, terminal groups and topological structure. Sequence information decoding is easily achieved according to Maldi-Tof mass spectrum without retrospecting its synthetic history, resulting in a great superiority in the field of information transmitting and reading. The resulting multifunctional sequence-defined polymers are water-soluble and positively charged, opening the avenue to bioapplications such as condensing DNA, gene transfection and drug delivery.

Stereocomplexes of Discrete, Isotactic Lactic Acid Oligomers Conjugated with Oligodimethylsiloxanes

Discrete length block co-oligomers (BCOs) comprised of a crystalline and an amorphous block are a new class of materials that gives highly ordered lamellar morphologies at small length scales. Here, we show the preparation of discrete, isotactic oligo l- and d-lactic acid (olLA and odLA) homoblocks followed by ligation to oligodimethylsiloxane (oDMS), affording a library of crystalline-amorphous BCOs that vary in molecular weight and composition. Mixing the two enantiomeric BCOs or homoblocks results in the formation of the corresponding stereocomplex. The properties and phase behavior of the isotactic (block co)oligomers and the stereocomplexes thereof are studied using differential scanning calorimetry and small-angle X-ray scattering. A systematic study of the isotactic homoblock lengths and crystal structure confirmed the formation of a 103 helix with a monomeric rise of 0.3 nm, whereas the stereocomplex adopts a 31 helix. The same type of crystal structure was found for the isotactic and stereocomplex of BCOs giving rise to the formation of lamellar morphologies at room temperature as a result of crystallization of the oLA blocks. Distorted lamellar structures were found in BCOs that preorganize into nonlamellar morphologies prior to crystallization. The stereocomplex BCOs shows more crystal defects and a loss of long-range ordering in the microstructure due to the larger driving force for crystallization. Hence, the balance between chain length, block volume, and the crystallization strength are of major importance for the formation of the final structure with the least defects.

Elucidation of the properties of discrete oligo(meth)acrylates

Discrete (monodisperse) methyl methacrylate (MMA) and di(ethylene glycol) ethyl ether acrylate (DEGEEA) oligomer libraries are generated via a 2-step process of RAFT polymerization and chromatographic separation.

Sequence-defined multifunctional polyethers via liquid-phase synthesis with molecular sieving

Synthetic chemists have devoted tremendous effort towards the production of precision synthetic polymers with defined sequences and specific functions. However, the creation of a general technology that enables precise control over monomer sequence, with efficient isolation of the target polymers, is highly challenging. Here, we report a robust strategy for the production of sequence-defined synthetic polymers through a combination of liquid-phase synthesis and selective molecular sieving. The polymer is assembled in solution with real-time monitoring to ensure couplings proceed to completion, on a three-armed star-shaped macromolecule to maximize efficiency during the molecular sieving process. This approach is applied to the construction of sequence-defined polyethers, with side-arms at precisely defined locations that can undergo site-selective modification after polymerization. Using this versatile strategy, we have introduced structural and functional diversity into sequence-defined polyethers, unlocking their potential for real-life applications in nanotechnology, healthcare and information storage.

Stereocomplex Prodrugs of Oligo(lactic acid) n-Gemcitabine in Poly(ethylene glycol)- block-poly(d,l-lactic acid) Micelles for Improved Physical Stability and Enhanced Antitumor Efficacy

Herein we demonstrate the formation of stereocomplex prodrugs of oligo(l-lactic acid) _n-gemcitabine (o(LLA) _n-GEM) and oligo(d-lactic acid) _n-gemcitabine (o(DLA) _n-GEM) for stable incorporation in poly(ethylene glycol)- block-poly(d,l-lactic acid) (PEG- b-PLA) micelles. O(LLA) _n or o(DLA) _n was attached at the amino group (4-( N)) of GEM via an amide linkage. When n = 10, a 1:1 mixture of o(LLA)₁₀-GEM and o(DLA)₁₀-GEM (o(L+DLA)₁₀-GEM) was able to form a stereocomplex with a distinctive crystalline pattern. Degradation of o(L+DLA)₁₀-GEM was driven by both backbiting conversion and esterase contribution, generating primarily o(L+DLA)₁-GEM and GEM. O(L+DLA)₁₀-GEM stably loaded in PEG- b-PLA micelles in the size range of 140-200 nm with an unexpected elongated morphology. The resulting micelles showed improved physical stability in aqueous media and inhibited backbiting conversion of o(L+DLA)₁₀-GEM within micelles. Release of o(L+DLA)₁₀-GEM from micelles was relatively slow, with a t_1/2 at ca. 60 h. Furthermore, weekly administration of o(L+DLA)₁₀-GEM micelles i.v. displayed potent antitumor activity in an A549 human non-small-cell lung carcinoma xenograft model. Thus, stereocomplexation of isotactic o(LLA) _n and o(DLA) _n acts as a potential prodrug strategy for improved stability and sustained drug release in PEG- b-PLA micelles.