<i>Ring-and-Lock</i> Interactions in Self-Healable Styrenic Copolymers

Commodity copolymers offer many useful applications, and their durability is critical in maintaining desired functions and retaining sustainability. These studies show that primarily alternating styrene/n-butyl acrylate [p(Sty/nBA)] copolymers self-heal without external intervention when monomer molar ratios are within the 45:55–53:47 range. This behavior is attributed to the favorable interchain interactions between aliphatic nBA side groups being sandwiched by aromatic rings forming ring-and-lock associations driven by pi–sigma–pi (π–σ–π) interactions. Guided by molecular dynamics (MD) simulations combined with spectroscopic and thermomechanical analysis, the ring-and-lock interchain van der Waals forces between π orbitals of aromatic rings and sigma components of aliphatic side groups are responsible for self-healing. Despite the frequent occurrence of these interactions in biological systems (proteins, nucleic acids, lipids, and polysaccharides), these largely unexplored weak and ubiquitous molecular forces between the soft acid aliphatic and soft base aromatic electrons may be valuable assets in the development of polymeric materials with sustainable properties

<i>Ring-and-Lock</i> Interactions in Self-Healable Styrenic Copolymers

Commodity copolymers offer many useful applications, and their durability is critical in maintaining desired functions and retaining sustainability. These studies show that primarily alternating styrene/n-butyl acrylate [p(Sty/nBA)] copolymers self-heal without external intervention when monomer molar ratios are within the 45:55–53:47 range. This behavior is attributed to the favorable interchain interactions between aliphatic nBA side groups being sandwiched by aromatic rings forming ring-and-lock associations driven by pi–sigma–pi (π–σ–π) interactions. Guided by molecular dynamics (MD) simulations combined with spectroscopic and thermomechanical analysis, the ring-and-lock interchain van der Waals forces between π orbitals of aromatic rings and sigma components of aliphatic side groups are responsible for self-healing. Despite the frequent occurrence of these interactions in biological systems (proteins, nucleic acids, lipids, and polysaccharides), these largely unexplored weak and ubiquitous molecular forces between the soft acid aliphatic and soft base aromatic electrons may be valuable assets in the development of polymeric materials with sustainable properties

Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP)

Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(<i>N</i>,<i>N</i>-dimethylamino)­ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (>10⁶ g/mol) molecular weight pDMAEMA-<i>b</i>-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli

One-Step Synthesis of Amphiphilic Ultrahigh Molecular Weight Block Copolymers by Surfactant-Free Heterogeneous Radical Polymerization

Ultrahigh molecular weight (>10⁶ g/mol) amphiphilic block copolymers were synthesized using one-step surfactant-free heterogeneous radical polymerization (SFHRP). The polymerization initially involves formation of water-soluble homopolymer blocks, followed by copolymerization of a hydrophobic monomer, resulting in ultrahigh molecular weight block copolymers. Facilitating heterogeneous reaction conditions and continuous supply of an initiator controls the process. Using this synthetic approach, we synthesized amphiphilic block copolymers of poly­(2-(<i>N</i>,<i>N</i>-dimethylamino)­ethyl methacrylate)-<i>block</i>-poly­(<i>n</i>-butyl acrylate) (pDMAEMA-<i>b</i>-pnBA), pDMAEMA-<i>block</i>-p­(<i>tert</i>-butyl acrylate) (pDMAEMA-<i>b</i>-tBA), and pDMAEMA-<i>block</i>-polystyrene (pDMAEMA-<i>b</i>-pSt) with molecular weights of 1.98 × 10⁶, 1.18 × 10⁶, and 0.91 × 10⁶ g/mol, respectively. These ultrahigh molecular weight block copolymers can self-assemble in nonpolar solvents to form thermochromic inverse polymeric micelles as well as other shapes and exhibit many potential applications

Tri-Phasic Size- and Janus Balance-Tunable Colloidal Nanoparticles (JNPs)

These studies show synthesis of triphasic size- and Janus balance (JB)-tunable nanoparticles (JNPs) utilizing a two-step emulsion polymerization of pentafluorostyrene (PFS) and 2-(dimethylamino)­ethyl methacrylate (DMAEMA) and <i>n</i>-butyl acrylate (nBA) in the presence of poly­(methyl methacrylate (MMA)/nBA) nanoparticle seeds. Each JNP consists of three phase-separated copolymers: p­(MMA/nBA) core, temperature, and pH-responsive (p­(DMAEMA/nBA)) phase capable of reversible size and shape changes, and shape-adoptable (p­(PFS/nBA)) phase. Due to built-in second-order lower critical solution temperature (II-LCST) transition of p­(DMAEMA/nBA) copolymer, macromolecular segments collapse when temperature increases from 30 to 45 °C, resulting in size and shape changes. The p­(DMAEMA/nBA) and p­(MMA/nBA) phases within each JNP assume concave, flat, or convex shapes, forcing p­(PFS/nBA) phase to adopt convex, planar, or concave interfacial curvatures, respectively. As a result, the JB can be tuned from 3.78 to 0.72. The presence of pH-responsive DMAEMA component also facilitates the size and JB changes due to protonation of the tertiary amine groups of p­(DMAEMA/nBA) backbone. Synthesized in this manner, JNPs are capable of stabilizing oil droplets in water at high pH to form Pickering emulsions, which at lower pH values release oil phase. This process is reversible and can be repeated many times

Expandable Temperature-Responsive Polymeric Nanotubes

Materials with the ability of dimensional changes on demand exhibit many potential applications ranging from adaptive composites that mimic biological functions under extreme conditions to microfluidics or neural implants to stimulate components of the nervous systems. These studies show the synthesis of temperature-induced reversibly expandable nanotubes that were prepared by polymerization of <i>N</i>-isopropylacrylamide (NIPAAM) in the presence of biologically active 1,2-bis­(tricosa-10,12-diynoyl)-<i>sn</i>-glycero-3-phosphocholine (DC_8,9PC) diacetylenic phospholipids (PL). As a result, thermally responsive poly-NIPAM-phospholipid nanotubes (PNNTs) were prepared. Polymerization reactions occur within hydrophilic regions of PL bilayers, whereas PL hydrophobic zones facilitate transport and supply of the monomer for polymerization. The unique feature of PNNTs is that, above 37 °C, the outer diameter (OD) as well as the wall thickness (WT) shrink by 20 and 55%, respectively, whereas the inner diameter (ID) increases by ∼16%. This behavior is attributed to the PNIPAM backbone buckling induced by local rearrangements within PL bilayered morphologies. The presence of acetylenic moieties along the PL bilayers in PNNTs provides an opportunity for irreversible “locking” of designable dimensions, which is facilitated by the formation of cross-linked PNNTs (CL-PNNTs)

Phage-Bacterium War on Polymeric Surfaces: Can Surface-Anchored Bacteriophages Eliminate Microbial Infections?

These studies illustrate synthetic paths to covalently attach T1 and Φ11 bacteriophages (phages) to inert polymeric surfaces while maintaining the bacteriophage’s biological activities capable of killing deadly human pathogens. The first step involved the formation of acid (COOH) groups on polyethylene (PE) and polytetrafluoroethylene (PTFE) surfaces using microwave plasma reactions in the presence of maleic anhydride, followed by covalent attachment of T1 and Φ11 species via primary amine groups. The phages effectively retain their biological activity manifested by a rapid infection with their own DNA and effective destruction of Escherichia coli and Staphylococcus aureus human pathogens. These studies show that simultaneous covalent attachment of two biologically active phages effectively destroy both bacterial colonies and eliminate biofilm formation, thus offering an opportunity for an effective combat against multibacterial colonies as well as surface detections of other pathogens