ACS Macro Letters

The formation of nanostructured shape anisotropic nanoparticles from poly(ferrocenylsilane)-b-poly(2-vinylpyridine) (PFS-b-P2VP) block copolymers is presented. Ellipsoidal particles with an axially stacked lamellar structure and nanosheets with a hexagonal structure of PFS cylinders are obtained under neutral wetting conditions through the use of a mixed surfactant system during self-assembly. In contrast to traditional systems, the resulting particle structure is strongly influenced by crystallization of the PFS domains under colloidal confinement with lamella-forming PFS-b-P2VP block copolymers leading to cylindrical morphologies. A blending approach was developed to control this morphological change and by the addition of PFS homopolymers, ellipsoidal particles with a lamellar structure could also be obtained. Ultimately, the spatial control over two orthogonal functionalities was exploited to demonstrate morphology transitions for nanosheets upon the exposure to methanol as solvent for P2VP and FeCl3 as a redox stimulus, opening up a variety of applications in the field of stimuli-responsive materials.

Surface-initiated polymerizations represent a versatile toolbox to generate densely grafted assemblies of chain end-tethered polymers. At sufficiently short interchain distances, surface-grafted polymers are forced into an extended chain conformation, which forms the basis of several unique properties, including their ability to withstand efficiently biofouling or to act as low friction coatings. While the effect on materials properties is well-established, only relatively recently first reports have appeared describing that chain stretching in surface-grafted polymer films also impacts chemical stability/reactivity. This Viewpoint presents surface-initiated polymerization as an alternative polymer mechanochemical tool. The absence of an external force field to induce chain elongation and the possibility to modulate chain stretching by varying brush molecular weight and grafting density, in conjunction with electrostatic interactions and nanoinclusions that may be present inside the polymeric grafts, make surface-initiated polymerization an attractive tool to both study and understand the effects of polymer chain conformation on the stability/reactivity of surface-grafted polymers.

We combine supramolecular host-guest interactions of β-cyclodextrin (CD) with light-induced Diels-Alder reactions of 2-methoxy-6-methylbenzaldehyde (photoenol, PE) for the formation of multiblock copolymers. Via the synthesis of a new bifunctional chain transfer agent (CTA) and subsequent reversible addition-fragmentation chain transfer (RAFT) polymerization, we introduce a supramolecular recognition unit (tert-butyl phenyl) and a photoactive unit (photoenol) to a polymer chain in order to obtain an α,ω-functionalized polymeric center block, having orthogonal recognition units at each chain end. Multiblock copolymers are formed via the light-induced reaction of the photoenol with a maleimide-functionalized polymer chain and the supramolecular self-assembly of the tert-butyl phenyl group with the β-CD end group of a third polymer chain. By employing the fast and efficient photoinduced Diels-Alder reaction in combination with supramolecular host-guest interactions, a novel method for macromolecular modular ligation is introduced.

A unique copolymer stabilizer is presented that can be used to stabilize multiwalled carbon nanotubes in aqueous solution to form "smart" dispersions. They showed double stimuli-responsive behavior (in dependence of temperature and ionic strength) and allowed for accurate control of the transition (exfoliated → agglomerated) temperature of nanotubes over a wide temperature range. In spite of its effective dispersion strength, the copolymer was easily synthesized in one step via free radical copolymerization of N-isopropylacrylamide and 1-ethyl-3-vinylimidazolium bromide.

We report the design and development of a new class of alkoxyphenacyl based photodegradable polycarbonates. These polymers incorporate the photoactive moiety in the backbone and, when irradiated at 300 nm, undergo controlled chain scission. Micropatterned thin films of these polymers were fabricated by photolithographic techniques. The use of these photodegradable polymers for controlled release applications was demonstrated by the release of Nile Red from polymeric nanoparticles. In addition, these polymers are mechanically robust, thermally stable, and hydrolytically degradable.

Polymers containing organoboronic acids have recently gained interest as sugar-responsive materials owing to the reversible binding of saccharides to boronic acids, which triggers a change in the physical and chemical properties of these polymers, such as their water solubility. In particular, the ability of these polymers to bind glucose has attracted considerable attention because of the promise of these materials for the development of sensors and drug delivery systems for glucose-related human diseases, such as diabetes. We report here a new class of sugar-responsive polymers that are based on a sequence-specific copolymer of styreneboroxole and N-functionalized maleimide. The reversible addition-fragmentation and chain transfer (RAFT) polymerization of this pair of monomers ensured that a glucose receptor alternates with a nonresponsive solubilizing group throughout the sugar-responsive polymer chain. Due to the presence of hydrophilic solubilizing groups beween the solubility-switching boroxole moieties in the membrane-forming block, the polymersomes of the block copolymers responded to a lower level of glucose in the medium, resulting in diassembly of the bilayer membrane under a physiologically relevant pH and glucose level.

Modeling and simulations of compartmentalization effects in tandem with nitroxide exit and entry have been performed for the nitroxide-mediated radical polymerization (NMP) of styrene in an aqueous dispersed system employing 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) at 125 °C. It is demonstrated that, even for a relatively water-insoluble nitroxide like TEMPO, exit and entry can strongly influence the polymerization kinetics in submicrometer-size droplets/particles. In such systems, the polymerization is expected to proceed at a markedly higher rate than the corresponding bulk system at the expense of control/livingness. Depending on the deactivator water solubility, these findings will apply qualitatively to all controlled/living radical polymerization systems governed by the persistent radical effect [e.g., NMP and atom transfer radical polymerization (ATRP)].

We present computer simulations of concentrated solutions of unknotted nonconcatenated semiflexible ring polymers. Unlike in their flexible counterparts, shrinking involves a strong energetic penalty, favoring interpenetration and clustering of the rings. We investigate the slow dynamics of the centers-of-mass of the rings in the amorphous cluster phase, consisting of disordered columns of oblate rings penetrated by bundles of prolate ones. Scattering functions reveal a striking decoupling of self- and collective motions. Correlations between centers-of-mass exhibit slow relaxation, as expected for an incipient glass transition, indicating the dynamic arrest of the cluster positions. However, self-correlations decay at much shorter time scales. This feature is a manifestation of the fast, continuous exchange and diffusion of the individual rings over the matrix of clusters. Our results reveal a novel scenario of glass formation in a simple monodisperse system, characterized by self-collective decoupling, soft caging, and mild dynamic heterogeneity.

This study describes a facile and high yielding route to two series of polymethacrylates inspired by the naturally occurring, tryptophan-rich cationic antimicrobial polymers. Appropriate optimization of indole content within each gave rise to polymers with high potency against Staphylococcus epidermidis (e.g., PGI-3 minimum inhibitory concentration (MIC) = 12 μg/mL) and the methicillin-resistant strain of Staphylococcus aureus (e.g., PGI-3 MIC = 47 μg/mL) with minimal toxicity toward human red blood cells. Future work will be directed toward understanding the cooperative roles that the cationic and indole pendant groups have for the mechanism of these polymers.

O-benzyl-L-serine carboxyanhydrides were synthesized via diazotization of O-benzyl-L-serine with sodium nitrite in aqueous sulfuric acid solution followed by cyclization of the resulting serine-based α-hydroxy acid with phosgene. Degradable, water-soluble poly(α-hydroxy acids) bearing pendant hydroxyl groups were readily prepared under mild conditions via ring-opening polymerization of O-benzyl-L-serine carboxyanhydrides followed by removal of the benzyl group and showed excellent cell compatibility, suggesting their potential being used as novel materials in constructing drug delivery systems and as hydrogel scaffolds for tissue engineering applications.

Understanding the local packing structures of a disordered mesomorphic phase is a challenging issue in polymer characterization. In this work, 13C-13C through-space interactions, as well as a molecular dynamics analysis based on the reorientation of chemical shift anisotropy (CSA), were proposed for the evaluation of the local packing structure of the mesomorphic form of isotactic polypropylene (iPP). 13C-13C double quantum (DQ) buildup curves of 13C 15% CH3 selectively labeled iPP and spin-dynamics simulations demonstrated that the local packing structures in the mesomorphic form were very similar to the packing in the β phase. Moreover, centerband only detection of exchange (CODEX) NMR proved that the correlation time ⟨τc⟩ of the overall stem dynamics in the mesomorphic form followed the same Arrhenius line observed for the β phase, but it deviated from that for the α phase. Based on both structural and dynamic results, it was concluded that the local packing structure in the mesomorphic form was exceedingly close or the same as that of the β phase.

A simple and low-cost “pen-writing” method is exploited for integrating conducting polymer on cellulosic paper. The pen-written paper chip not only possesses excellent mechanical and electrical properties, but also serves as a versatile sensor, fulfilling several real-time and in situ detections for ammonia gas, thermal heating, and NIR light. The theoretical detection limit of ammonia gas can be as low as 1.2 ppm, which is a promising performance for industrial application. In addition, this “pen-writing” technique can be extended to generate wearable electrical textiles in a large scale.