Construction of a Reactive Diblock Copolymer, Polyphosphoester-<i>block</i>-Poly(l‑lactide), as a Versatile Framework for Functional Materials That Are Capable of Full Degradation and Nanoscopic Assembly Formation

The development of a diblock copolymer, polyphosphoester-<i>block</i>-poly­(l-lactide), which has potential for being fully degradable and biocompatible, was achieved by one-pot sequential ring-opening polymerizations (ROPs) of two cyclic monomers: alkyne-functionalized phospholane and l-lactide (LLA). A kinetic study of the polymerization in each step was investigated in a detailed manner by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC), revealing living/controlled characteristics with narrow molecular weight distributions and a linear increase of molecular weights vs monomer conversion and time. Subsequently, photoinduced thiol-yne “click” reactions with small-molecule thiols bearing either carboxylic acid or amino groups afforded amphiphilic diblock copolymers with carboxylate or amino side-chain functionalities along the polyphosphoester segment of the diblock copolymer backbone. Finally, direct dissolution of the two different types of amphiphilic diblock copolymers in aqueous solutions yielded well-defined spherical micelles with corresponding negative or positive surface charges, respectively, as confirmed by transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential analyses

Detection of Living Anionic Species in Polymerization Reactions Using Hyperpolarized NMR

Intermediates during the anionic polymerization of styrene were observed using hyperpolarized NMR. Dissolution dynamic nuclear polarization (DNP) of monomers provides a sufficient signal-to-noise ratio for detection of ¹³C NMR signals in real time as the reaction progresses. Because of its large chemical shift dispersion, ¹³C is well-suited to distinguish and characterize the chemical species that arise during the reaction. At the same time, incorporation of hyperpolarized small-molecule monomers is a unique way to generate polymers that exhibit a transient signal enhancement at the active site. This strategy is applicable despite the decay of the hyperpolarization of the polymer due to rapid spin–lattice relaxation. Real-time measurements on polymerization reactions provide both mechanistic and kinetic information without the need for stable isotope labeling of the molecules of interest. These capabilities are orthogonal to currently established methods that separate synthesis and analysis into two steps, making dissolution DNP an attractive method to study polymerization reactions

Functionalizable Hydrophilic Polycarbonate, Poly(5-methyl-5-(2-hydroxypropyl)aminocarbonyl-1,3-dioxan-2-one), Designed as a Degradable Alternative for PHPMA and PEG

Drawbacks of poly­(ethylene glycol) (PEG), the most widely used water-soluble polymer in nanomedicines, have stimulated development of alternative hydrophilic polymers. Among the substitutes, poly­(<i>N</i>-(2-hydroxypropyl)­methacrylamide) (PHPMA) exhibits water solubility, minimal toxicity, and the possibility to introduce functionalities through pendant hydroxyl groups; however, nondegradability may cause long-term health and environmental issues. Alternatively, polycarbonates based on bis-MPA derivatives, which are well-known to be biocompatible, biodegradable, and of low toxicity <i>in vivo</i>, could be utilized as degradable equivalents to polymethacrylates. Therefore, we developed a polycarbonate-based PHPMA analogue, poly­(5-methyl-5-(2-hydroxypropyl)­aminocarbonyl-1,3-dioxan-2-one) (PMHPAC), by amidation of carboxylic acid-functional polycarbonates with 1-amino-2-propanol. The resulting PMHPAC was highly water-soluble, with low cyto-/immuno-toxicities, and readily functionalizable. These characteristics make PMHPAC a promising candidate as a degradable alternative to PEG and PHPMA. Furthermore, a fully degradable PMHPAC block copolymer was synthesized to demonstrate synthetic versatility and formation of nanostructures in aqueous solution for potential biomedical applications

Poly(d‑glucose carbonate) Block Copolymers: A Platform for Natural Product-Based Nanomaterials with Solvothermatic Characteristics

A natural product-based polymer platform, having the characteristics of being derived from renewable materials and capable of breaking down, ultimately, into natural byproducts, has been prepared through the ring-opening polymerization (ROP) of a glucose-based bicyclic carbonate monomer. ROP was carried out via chain extension of a polyphosphoester (PPE) macroinitiator in the presence of 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD) organocatalyst to afford the PPE-<i>b</i>-poly­(d-glucose carbonate) (PDGC) block copolymer. This new copolymer represents a functional architecture that can be rapidly transformed through thiol-yne reactions along the PPE segment into a diverse variety of amphiphilic polymers, which interestingly display stimuli-sensitive phase behavior in the form of a lower critical solution temperature (LCST). Below the LCST, they undergo self-assembly to form spherical core–shell nanostructures that display a poorly defined core–shell morphology. It is expected that hydrophobic patches are exposed within the micellar corona, reminiscent of the surface complexity of proteins, making these materials of interest for triggered and reversible assembly disassembly processes

A Vinyl Ether-Functional Polycarbonate as a Template for Multiple Postpolymerization Modifications

A highly reactive vinyl ether-functionalized aliphatic polycarbonate and its block copolymer were developed as templates for multiple postpolymerization conjugation chemistries. The vinyl ether-functional six-membered cyclic carbonate monomer was synthesized by a well-established two-step procedure starting from 2,2-bis­(hydroxymethyl)­propionic acid. An organobase-catalyzed ring-opening polymerization of the synthesized monomer afforded polycarbonates with pendant vinyl ether functionalities (PMVEC). The vinyl ether moieties on the resulting polymers were readily conjugated with hydroxyl- or thiol-containing compounds via three different postpolymerization modification chemistries: acetalization, thio-acetalization, and thiol–ene reaction. Acetal-functionalized polycarbonates were studied in depth to exploit their acid-labile acetal functionalities. Acetalization of the amphiphilic diblock copolymer of poly­(ethylene glycol) methyl ether (mPEG) and PMVEC, mPEG₁₁₃-<i>b</i>-PMVEC₁₃, with the model hydroxyl compound 4-methylbenzyl alcohol resulted in a maximum of 42% acetal and 58% hydroxyl side chain groups. Nonetheless, the amphiphilicity of the block polymer allowed for its self-assembly in water to afford nanostructures, as characterized via dynamic light scattering and transmission electron microscopy. The kinetics of acetal cleavage within the block polymer micelles were examined in acidic buffered solutions (pH 4 and 5). In addition, mPEG-<i>b</i>-PMVEC and its hydrolyzed polymer mPEG-<i>b</i>-PMHEC (i.e., after full cleavage of acetals) exhibited minimal cytotoxicity to RAW 264.7 mouse macrophages, indicating that this polymer system represents a biologically nonhazardous material with pH-responsive activity

Development of a Vinyl Ether-Functionalized Polyphosphoester as a Template for Multiple Postpolymerization Conjugation Chemistries and Study of Core Degradable Polymeric Nanoparticles

A novel polyphosphoester (PPE) with vinyl ether side chain functionality was developed as a versatile template for postpolymerization modifications, and its degradability and biocompatibility were evaluated. An organocatalyzed ring-opening polymerization of ethylene glycol vinyl ether-pendant cyclic phosphotriester monomer allowed for construction of poly­(ethylene glycol vinyl ether phosphotriester) (PEVEP). This vinyl ether-functionalized PPE scaffold was coupled with hydroxyl- or thiol-containing model small molecules via three different types of conjugation chemistriesthiol–ene “click” reaction, acetalization, or thio-acetalization reactionto afford modified polymers that accommodated either stable thio–ether or hydrolytically labile acetal or thio–acetal linkages. Amphiphilic diblock copolymers of poly­(ethylene glycol) and PEVEP formed well-defined micelles with a narrow and monomodal size distribution in water, as confirmed by dynamic light scattering (DLS), transmission electron microscopy, and atomic force microscopy. The stability of the micelles and the hydrolytic degradability of the backbone and side chains of the PEVEP block segment were assessed by DLS and nuclear magnetic resonance spectroscopy (¹H and ³¹P), respectively, in aqueous buffer solutions at pH values of 5.0 and 7.4 and at temperatures of 25 and 37 °C. The hydrolytic degradation products of the PEVEP segments of the block copolymers were then identified by electrospray ionization, gas chromatography, and matrix-assisted laser desorption/ionization mass spectrometry. The parent micelles and their degradation products were found to be non-cytotoxic at concentrations up to 3 mg/mL, when evaluated with RAW 264.7 mouse macrophages and OVCAR-3 human ovarian adenocarcinoma cells

Holistic Assessment of Covalently Labeled Core–Shell Polymeric Nanoparticles with Fluorescent Contrast Agents for Theranostic Applications

The successful development of degradable polymeric nanostructures as optical probes for use in nanotheranostic applications requires the intelligent design of materials such that their surface response, degradation, drug delivery, and imaging properties are all optimized. In the case of imaging, optimization must result in materials that allow differentiation between unbound optical contrast agents and labeled polymeric materials as they undergo degradation. In this study, we have shown that use of traditional electrophoretic gel-plate assays for the determination of the purity of dye-conjugated degradable nanoparticles is limited by polymer degradation characteristics. To overcome these limitations, we have outlined a holistic approach to evaluating dye and peptide–polymer nanoparticle conjugation by utilizing steady-state fluorescence, anisotropy, and emission and anisotropy lifetime decay profiles, through which nanoparticle–dye binding can be assessed independently of perturbations, such as those presented during the execution of electrolyte gel-based assays. This approach has been demonstrated to provide an overall understanding of the spectral signature–structure–function relationship, ascertaining key information on interactions between the fluorophore, polymer, and solvent components that have a direct and measurable impact on the emissive properties of the optical probe. The use of these powerful techniques provides feedback that can be utilized to improve nanotheranostics by evaluating dye emissivity in degradable nanotheranostic systems, which has become increasingly important as modern platforms transition to architectures intentionally reliant on degradation and built-in environmental responses

Preparation and <i>in Vitro</i> Antimicrobial Activity of Silver-Bearing Degradable Polymeric Nanoparticles of Polyphosphoester-<i>block</i>-Poly(l‑lactide)

The development of well-defined polymeric nanoparticles (NPs) as delivery carriers for antimicrobials targeting human infectious diseases requires rational design of the polymer template, an efficient synthetic approach, and fundamental understanding of the developed NPs, <i>e.g.,</i> drug loading/release, particle stability, and other characteristics. Herein, we developed and evaluated the <i>in vitro</i> antimicrobial activity of silver-bearing, fully biodegradable and functional polymeric NPs. A series of degradable polymeric nanoparticles (dNPs), composed of phosphoester and l-lactide and designed specifically for silver loading into the hydrophilic shell and/or the hydrophobic core, were prepared as potential delivery carriers for three different types of silver-based antimicrobials–silver acetate or one of two silver carbene complexes (SCCs). Silver-loading capacities of the dNPs were not influenced by the hydrophilic block chain length, loading site (<i>i.e.</i>, core or shell), or type of silver compound, but optimization of the silver feed ratio was crucial to maximize the silver loading capacity of dNPs, up to <i>ca.</i> 12% (w/w). The release kinetics of silver-bearing dNPs revealed 50% release at <i>ca.</i> 2.5–5.5 h depending on the type of silver compound. In addition, we undertook a comprehensive evaluation of the rates of hydrolytic or enzymatic degradability and performed structural characterization of the degradation products. Interestingly, packaging of the SCCs in the dNP-based delivery system improved minimum inhibitory concentrations up to 70%, compared with the SCCs alone, as measured <i>in vitro</i> against 10 contemporary epidemic strains of Staphylococcus aureus and eight uropathogenic strains of Escherichia coli. We conclude that these dNP-based delivery systems may be beneficial for direct epithelial treatment and/or prevention of ubiquitous bacterial infections, including those of the skin and urinary tract