Linear and Star Poly(ionic liquid) Assemblies: Surface Monolayers and Multilayers

The surface morphology and organization of poly­(ionic liquid)­s (PILs), poly­[1-(4-vinylbenzyl)-3-butylimidazolium bis­(trifluoromethylsulfonyl)­imide] are explored in conjunction with their molecular architecture, adsorption conditions, and postassembly treatments. The formation of stable PIL Langmuir and Langmuir–Blodgett (LB) monolayers at the air–water and air–solid interfaces is demonstrated. The hydrophobic bis­(trifluoromethylsulfonyl)­imide (Tf₂N^–) is shown to be a critical agent governing the assembly morphology, as observed in the reversible condensation of LB monolayers into dense nanodroplets. The PIL is then incorporated as an unconventional polyelectrolyte component in the layer-by-layer (LbL) films of hydrophobic character. We demonstrate that the interplay of capillary forces, macromolecular mobility, and structural relaxation of the polymer chains influence the dewetting mechanisms in the PIL multilayers, thereby enabling access to a diverse set of highly textured, porous, and interconnected network morphologies for PIL LbL films that would otherwise be absent in conventional LbL films. Their compartmentalized internal structure is relevant to molecular separation membranes, ultrathin hydrophobic coatings, targeted cargo delivery, and highly conductive films

A Simple and Universal Gel Permeation Chromatography Technique for Precise Molecular Weight Characterization of Well-Defined Poly(ionic liquid)s

Poly­(ionic liquid)­s (PILs) are an important class of technologically relevant materials. However, characterization of well-defined polyionic materials remains a challenge. Herein, we have developed a simple and versatile gel permeation chromatography (GPC) methodology for molecular weight (MW) characterization of PILs with a variety of anions. PILs with narrow MW distributions were synthesized via atom transfer radical polymerization, and the MWs obtained from GPC were further confirmed via nuclear magnetic resonance end group analysis

Synthesis of High Molecular Weight Polymethacrylates with Polyhedral Oligomeric Silsesquioxane Moieties by Atom Transfer Radical Polymerization

A new polyhedral oligomeric silsesquioxane (POSS) methacrylate monomer, 1-(3-(methacryloyloxy)­propyl)­dimethylsiloxy-3,5,7,9,11,13,15-hepta­(isobutyl)­pentacyclo-[9.5.1.1^3,9.1^5,15.1^7,13]­octasiloxane ((i-Bu)₇POSS-OSiMe₂-MA, <b>1</b>), with a flexible spacer between the cubic POSS cage and methacrylate group was synthesized to reduce steric strain and thus achieve polymethacrylates (poly­(POSS-MA)­s) with high molecular weight (MW). Atom transfer radical polymerization (ATRP) of <b>1</b> at high monomer concentration (1 M, corresponding to ca. 85 wt % of <b>1</b>) led to polymers with the absolute number-average MW, determined by multiangle laser light scattering, <i>M</i>_n,_MALLS = 2 350 000 (and apparent MW, measured by gel permeation chromatography with linear poly­(methyl methacrylate) (PMMA) standards, <i>M</i>_n,GPC = 550 000). Optimization of the reaction conditions, including the ATRP catalyst, targeted degrees of polymerization, monomer concentrations, as well as a monomer feeding, resulting in the first well-defined high MW polymers with POSS moieties

Preparation of Polymeric Nanoscale Networks from Cylindrical Molecular Bottlebrushes

The design and control of polymeric nanoscale network structures at the molecular level remains a challenging issue. Here we construct a novel type of polymeric nanoscale networks with a unique microporous nanofiber unit employing the intra/interbrush carbonyl cross-linking of polystyrene side chains for well-defined cylindrical polystyrene molecular bottlebrushes. The size of the side chains plays a vital role in the tuning of nanostructure of networks at the molecular level. We also show that the as-prepared polymeric nanoscale networks exhibit high specific adsorption capacity per unit surface area because of the synergistic effect of their unique hierarchical porous structures. Our strategy represents a new avenue for the network unit topology and provides a new application for molecular bottlebrushes in nanotechnology

Syntheses of Monosubstituted Rhodocenium Derivatives, Monomers, and Polymers

We report the first chemoselective, high yield synthesis of monosubstituted rhodocenium through a “η⁵ → η⁴ → η⁵” strategy detailing sequential nucleophilic addition and endohydride abstraction. Monosubstituted rhodocenium derivatives are then used as versatile synthons for the preparation of the first-ever vinyl monomers that allow controlled polymerizations including ROMP and RAFT, leading to rhodocenium-containing metallopolymers. Exploratory ion-exchange and self-assembly of this new class of polyelectrolytes cultivates the potential of side-chain rhodocenium-containing polymers

Synthetic Lift-off Polymer beneath Layer-by-Layer Films for Surface-Mediated Drug Delivery

A broad range of biomaterials coatings and thin film drug delivery systems require a strategy for the immobilization, retention, and release of coatings from surfaces such as patches, inserts, and microneedles under physiological conditions. Here we report a polymer designed to provide a dynamic surface, one that first functions as a platform for electrostatic thin film assembly and releases the film once in an in vivo environment. Atom transfer radical polymerization (ATRP) was used to synthesize this polymer poly­(<i>o</i>-nitrobenzyl-methacrylate-<i>co</i>-hydroxyethyl-methacrylate-<i>co</i>-poly­(ethylene-glycol)-methacrylate) (PNHP), embedded beneath multilayered polyelectrolyte films. Such a base layer is designed to photochemically pattern negative charge onto a solid substrate, assist deposition of smooth layer-by-layer (LbL) polyelectrolyte in mildly acidic buffers and rapidly dissolve at physiological pH, thus lifting off the LbL films. To explore potential uses in the biomedical field, a lysozyme (Lys)/poly­(acrylic acid) (PAA) multilayer film was developed on PNHP-coated silicon wafers to construct prototype antimicrobial shunts. Film thickness was shown to grow exponentially with increasing deposition cycles, and effective drug loading and in vitro release was confirmed by the dose-dependent inhibition of Escherichia coli (E. coli) growth. The efficacy of this approach is further demonstrated in LbL-coated microscale needle arrays ultimately of interest for vaccine applications. Using PNHP as a photoresist, LbL films were confined to the tips of the microneedles, which circumvented drug waste at the patch base. Subsequent confocal images confirmed rapid LbL film implantation of PNHP at microneedle penetration sites on mouse skin. Furthermore, in human skin biopsies, we achieved efficient immune activation demonstrated by a rapid uptake of vaccine adjuvant from microneedle-delivered PNHP LbL film in up to 37% of antigen-presenting cells (APC), providing an unprecedented LbL microneedle platform for human vaccination

Biologically Derived Soft Conducting Hydrogels Using Heparin-Doped Polymer Networks

The emergence of flexible and stretchable electronic components expands the range of applications of electronic devices. Flexible devices are ideally suited for electronic biointerfaces because of mechanically permissive structures that conform to curvilinear structures found in native tissue. Most electronic materials used in these applications exhibit elastic moduli on the order of 0.1–1 MPa. However, many electronically excitable tissues exhibit elasticities in the range of 1–10 kPa, several orders of magnitude smaller than existing components used in flexible devices. This work describes the use of biologically derived heparins as scaffold materials for fabricating networks with hybrid electronic/ionic conductivity and ultracompliant mechanical properties. Photo-cross-linkable heparin–methacrylate hydrogels serve as templates to control the microstructure and doping of <i>in situ</i> polymerized polyaniline structures. Macroscopic heparin-doped polyaniline hydrogel dual networks exhibit impedances as low as <i>Z</i> = 4.17 Ω at 1 kHz and storage moduli of <i>G</i>′ = 900 ± 100 Pa. The conductivity of heparin/polyaniline networks depends on the oxidation state and microstructure of secondary polyaniline networks. Furthermore, heparin/polyaniline networks support the attachment, proliferation, and differentiation of murine myoblasts without any surface treatments. Taken together, these results suggest that heparin/polyaniline hydrogel networks exhibit suitable physical properties as an electronically active biointerface material that can match the mechanical properties of soft tissues composed of excitable cells

Single-Ion Homopolymer Electrolytes with High Transference Number Prepared by Click Chemistry and Photoinduced Metal-Free Atom-Transfer Radical Polymerization

Solvent-free single-ion polymer electrolytes with high conductivity have historically been prepared in the form of block copolymer or polymer blends. In this work, single-ion homopolymer electrolytes consisting of poly­(poly­(ethylene oxide) methacrylate lithium sulfonyl­(tri­fluoro­methyl­sulfonyl)­imide), poly­(PEOMA-TFSI^–Li⁺), were prepared for the first time by photoinduced metal-free atom-transfer radical polymerization. The PEO-based macromonomer PEOMA-TFSI^–Li⁺ was synthesized via click chemistry, copper-catalyzed alkyne–azide cycloaddition. Because of the conductive, amorphous PEO phase in which the lithium ions are located, these polymers showed improved ionic conductivity (10^–5–10^–4 S/cm at 90 °C) and high transference number (0.97–0.99). A continued lithium plating–stripping experiment was performed at current density ≥0.1 mA/cm² over 300 cycles at 90 °C. The potential dendrite-suppressing capability of the polymer with such high transference number was also estimated by employing a kinetic model using the measured transport and transference properties to study the current density at the dendrite tip. The analysis indicates that the synthesized polymers could have a high propensity to suppress dendrite growth