Polymer recycling is currently predicated on the separation of a vast array of chemically different and immiscible polymer chains. As a result, only a relatively small fraction of plastic waste is ultimately recycled. Overcoming the repulsion of chemically dissimilar polymeric chains would enable the formation of strong, optically clear, and useful materials to be obtained from mixed plastics recycling waste. Here, we demonstrate the utility of relatively sparse ionic bonds (approximate to 1.0 and 6.5 mol % functionalization of a polymer backbone) coupled with a sulfonic acid-to-imidazole base proton transfer mechanism to facilitate the formation of optically clear materials in otherwise incompatible poly(dimethylsiloxane) and poly(n-butyl acrylate) mixtures. Adjusting the degree of ionic functionality spans a spectrum from nanometer-scale assemblies driven by electrostatic interactions to fully homogeneous blends with unique viscoelastic characteristics. This study highlights the complex physics of sparsely charged polymer blends and their potential impact on addressing society's pressing plastic waste challenges.

A versatile synthetic platform is reported that affords high molecular weight graft copolymers containing polydimethylsiloxane (PDMS) backbones and vinyl-based polymer side chains with excellent control over molecular weight and grafting density. The synthetic approach leverages thiol-ene click chemistry to attach an atom-transfer radical polymerization (ATRP) initiator to a variety of commercially available poly(dimethylsiloxane-co-methylvinylsiloxane) backbones (PDMS-co-PVMS), followed by controlled radical polymerization with a wide scope of vinyl monomers. Selective degradation of the siloxane backbone with tetrabutylammonium fluoride confirmed the controlled nature of side-chain growth via ATRP, yielding targeted side-chain lengths for copolymers containing up to 50% grafting density and overall molecular weights in excess of 1 MDa. In addition, by using a mixture of thiols, grafting density and functionality can be further controlled by tuning initiator loading along the backbone. For example, solid-state fluorescence of the graft copolymers was achieved by incorporating a thiol-containing fluorophore along the siloxane backbone during the thiol-ene click reaction. This simple synthetic platform provides facile control over the properties of a wide variety of grafted copolymers containing flexible PDMS backbones and vinyl polymer side chains. image

Polyborosiloxanes are used in a variety of fields due to their unique dynamic properties. Traditionally, cross-linked polyborosiloxanes are prepared by incorporating boric acid into siloxane prepolymers, a process that is time-consuming, energy intensive, and challenging due to reagent immiscibility. Here, we report a versatile synthetic method to rapidly cure polyborosiloxane networks via hydrosilylation of chain end or backbone functionalized polydimethylsiloxane (PDMS) derivatives with an inexpensive trivinylboronate. Networks synthesized from these readily available building blocks cure in similar to 2 min at convenient temperatures (e.g., 90 degrees C) and exhibit enhanced viscoelastic behavior when compared to traditional polyborosiloxane networks fabricated via the conventional condensation route. By virtue of using efficient hydrosilylation chemistry, another key advantage of this synthetic platform is the ability to synthesize dynamic polyborosiloxanes with different network connectivity by simply using silicones with Si-H moieties placed at the chain ends (end-group) or distributed throughout the repeat-unit structure (pendant-group). The availability of other alkenes amenable to hydrosilylation provides an additional formulation handle to synthesize mixed dynamic-static networks with tunable control over stress relaxation and solvent resistance. In summary, the synthetic approach disclosed herein is a simple and accessible platform for preparing dynamic polyborosiloxanes with tunable material properties.

The synthetic utility of heterotelechelic polydimethylsiloxane (PDMS) derivatives is limited due to challenges in preparing materials with high chain-end fidelity. In this study, anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D3) monomers using a specifically designed silyl hydride (Si-H)-based initiator provides a versatile approach toward a library of heterotelechelic PDMS polymers. A novel initiator, where the Si-H terminal group is connected to a C atom (H-Si-C) and not an O atom (H-Si-O) as in traditional systems, suppresses intermolecular transfer of the Si-H group, leading to heterotelechelic PDMS derivatives with a high degree of control over chain ends. In situ termination of the D3 propagating chain end with commercially available chlorosilanes (alkyl chlorides, methacrylates, and norbornenes) yields an array of chain-end-functionalized PDMS derivatives. This diversity can be further increased by hydrosilylation with functionalized alkenes (alcohols, esters, and epoxides) to generate a library of heterotelechelic PDMS polymers. Due to the living nature of ring-opening polymerization and efficient initiation, narrow-dispersity (Đ < 1.2) polymers spanning a wide range of molar masses (2-11 kg mol-1) were synthesized. With facile access to α-Si-H and ω-norbornene functionalized PDMS macromonomers (H-PDMS-Nb), the synthesis of well-defined supersoft (G' = 30 kPa) PDMS bottlebrush networks, which are difficult to prepare using established strategies, was demonstrated.

Multiblock copolymers with increasingly complex block sequences- for example, triblock terpolymers-offer unique opportunities to create nano-structured materials, but this potential has been hindered by a vast design space that complicates the exploration of structure-property relationships. Here, we report a versatile and scalable strategy to separate parent ABC and isomeric ACB triblock terpolymers into libraries of fractionated samples spanning a wide range of compositions. Using a combination of controlled polymerization and automated chromatography, the synthesis and separation of less than 10 ABC and ACB parent materials gave rise to over 100 purified triblock terpolymers. Separations follow systematic and predictable trends in volume fraction resulting from an adsorption-based mechanism where chains rich in non-polar blocks elute first, followed by more polar derivatives, yielding fractions with improved purity in composition and molar-mass dispersity. As evidenced by small-angle X-ray scattering, fractionation significantly enhances long-range order compared to as-synthesized parent materials and allows for the definitive identification of various nanoscale morphologies. This user-friendly separation strategy significantly increases the availability of well-defined ABC triblock terpolymer libraries to the polymer community while also improving sample quality and accelerating discovery.

Polymer blending is a cost-effective way to control the properties of soft materials, but the propensity for blends to macrophase separate motivates the development of efficient compatibilization strategies. Across this broad area, compatibilization is particularly important for polysiloxanes, which exhibit strong repulsive interactions with most organic polymers. This review analyzes state-of-the-art polysiloxane compatibilization strategies for silicone–organic polymer blends. Emphasis is placed on chemical innovation in the design of compatibilization agents that may expedite the commercialization of new silicone–organic materials. We anticipate that hybrid silicone blends will continue to play an important role in fundamental and applied materials science across industry and academia.

Chemokines and chemokine receptors play an important role in the initiation and progression of atherosclerosis by mediating the trafficking of inflammatory cells. Chemokine receptor 5 (CCR5) has major implications in promoting the development of plaques to advanced stage and related vulnerability. CCR5 antagonist has demonstrated the effective inhibition of atherosclerotic progression in mice, making it a potential biomarker for atherosclerosis management. To accurately determine CCR5 in vivo, we synthesized CCR5 targeted Comb nanoparticles through a modular design and construction strategy with control over the physiochemical properties and functionalization of CCR5 targeting peptide d-Ala-peptide T-amide (DAPTA-Comb). In vivo pharmacokinetic evaluation through 64Cu radiolabeling showed extended blood circulation of 64Cu-DAPTA-Combs conjugated with 10%, 25%, and 40% DAPTA. The different organ distribution profiles of the three nanoparticles demonstrated the effect of DAPTA on not only physicochemical properties but also targeting efficiency. In vivo positron emission tomography/computed tomography (PET/CT) imaging in an apolipoprotein E knockout mouse atherosclerosis model (ApoE-/-) showed that the three 64Cu-DAPTA-Combs could sensitively and specifically detect CCR5 along the progression of atherosclerotic lesions. In an ApoE-encoding adenoviral vector (AAV) induced plaque regression ApoE-/- mouse model, decreased monocyte recruitment, CD68+ macrophages, CCR5 expression, and plaque size were all associated with reduced PET signals, which not only further confirmed the targeting efficiency of 64Cu-DAPTA-Combs but also highlighted the potential of these targeted nanoparticles for atherosclerosis imaging. Moreover, the up-regulation of CCR5 and colocalization with CD68+ macrophages in the necrotic core of ex vivo human plaque specimens warrant further investigation for atherosclerosis prognosis.

636 Objectives: It is unclear which asymptomatic patients with ≥ 70% diameter carotid stenosis may benefit from carotid endarterectomy (CEA) intervention. We have identified a natriuretic peptide receptor (NPRC) that is present in deep intimal macrophages and vascular smooth muscle cells and is up-regulated in plaque with features of instability. We have developed a nanoparticle radiotracer, 64Cu-CANF-Comb, directly targeting this receptor. We hypothesize that uptake of this radiotracer will correlate with both presence of NPRC on immunohistochemistry (IHC) of ex vivo carotid specimens in patients who went on to CEA surgery, and to features of instability (large lipid pool, hemorrhage). Methods: Fourteen patients (average age 73.5, range 60-85 years; 7 men, 7 women) scheduled for CEA underwent carotid PET/MRI imaging approximately 18 hours after injection of 3.5-5.1 mCi 64Cu-CANF-Comb. PET acquisition was list mode for ~ 30 min. MR imaging consisted of high-resolution (0.5-0.7 mm) bright blood 3D GRE, T2 3D SPACE, dark blood TSE T1, and T2/PD imaging using small neck surface coils. CEA specimens were collected post surgery for IHC. Eight specimens were stained with an antibody (anti-NPRC, 1:100 in blocking serum) and a secondary antibody labeled with a blue chromogen and counterstained with nuclear fast red. Five 100X random fields were randomly selected in the superficial intima, deep intima and media of the specimens. NPRC positive cells were counted in each field, and an average was derived for the 15 fields. A supervised classifier software program in Matlab was developed to segment the carotid MR images to determine the maximal morphological component (calcium, fibrous cap, lipid pool, hemorrhage). Highest PET SUV of plaque was compared to NPRC readout on IHC and to primary plaque component on MRI. Results: Highest SUV in the region of carotid stenotic plaque removed for CEA across subjects (N=8) ranged from 0.27-2.72, mean 1.18 (SD .82) and showed strong correlation with IHC presence of NPRC, r= 0.90, 95% CI (0.501, 0.980), P = 0.002. NPRC presence on IHC was highest in the deep intima. On MRI, SUV showed strong correlation with percent plaque volume of combined lipid rich necrotic core and hemorrhage, r= 0.90, 95% CI (0.469, 0.986), P = 0.007 (N=7). Conclusions: We have translated a receptor-targeted PET radiotracer, 64Cu-CANF-Comb, into human subjects and show that PET uptake correlates with plaque expression of NPRC, the receptor it targets. This receptor is expressed in deep intimal macrophages and vascular smooth muscle cells in carotid plaque with features of instability.

Discrete oligomers (i.e., highly monodisperse) can provide a deep understanding of chain-length-dependent properties of polymers and their self-assembly behaviors. Herein, discrete oligo(3-hexylthiophene)s (D-o3HTs) with a dispersity (D) of 1.0 and degree of polymerization (DP) between 6 and 18 were obtained through a simple synthetic procedure of 3-hexlythiophene trimer-based polymerizations and automated column chromatography purification. As the DP of D-o3HTs increases, longer conjugation lengths cause red shifts in their optical properties and yield tunable crystalline properties. Interestingly, D-o3HTs with DP = 12 assemble into a dominant edge-on Form I structure in thin films and show highly ordered fiber morphologies. In addition, Bragg rod patterns are observed in thin films by transmission electron microscopy and grazing incidence X-ray scattering with these patterns being distinctive when compared to those for conventional regioregular poly(3-hexylthiophene) with D = 1.1. Finally, the formation of 2-dimensional flowerlike nanostructures with overall micrometer dimensions is obtained from D-o3HTs via solvent-mediated self-assembly. These results offer an understanding of self-assembly behaviors of discrete conjugated polymers, leading to exquisite control over their crystallinity and nanoscale morphology.

DNA-mediated assembly of inorganic particles has demonstrated to be a powerful approach for preparing nanomaterials with a range of interesting optical and electrical properties. Building on this inspiration, we describe a generalizable gram-scale method to assemble nanoparticles through the formation of poly(methyl methacrylate) (PMMA) triple-helices. In this work, alkene-terminated syndiotactic (st-) and isotactic (it-) PMMA polymers were prepared and subsequently functionalized to afford nanoparticle ligands. Nanoparticles with complementary st- and it-PMMA ligands could then be spontaneously assembled upon mixing at room temperature. This process was robust and fully reversible through multiple heating and cooling cycles. The versatility of PMMA stereocomplexation was highlighted by assembling hybrid structures composed of nanoparticles of different compositions (e.g., Au and quantum dots) and shapes (e.g., spheres and rods). These initial demonstrations of nanoparticle self-assembly from inexpensive PMMA-based materials present an attractive alternative to DNA-based nanomaterials.

Herein we report the development of a merocyanine-based photoacid with improved solubility in organic media and enhanced switching kinetics that can be used to impart temporal control over ring opening polymerization. The effect of the structural modification on solubility, thermal relaxation kinetics and activation energy were evaluated using H-1 NMR and pump-probe absorption spectroscopies. Overall, the new merocyanine based photoacid provides access to a wider range of chemical and material applications with improved solvent compatibility and temporal control.

Inspired by nanotechnologies based on DNA strand displacement, herein we demonstrate that synthetic helical strand exchange can be achieved through tuning of poly(methyl methacrylate) (PMMA) triple-helix stereocomplexes. To evaluate the utility and robustness of helical strand exchange, stereoregular PMMA/polyethylene glycol (PEG) block copolymers capable of undergoing crystallization driven self-assembly via stereocomplex formation were prepared. Micelles with spherical or wormlike morphologies were formed by varying the molecular weight composition of the assembling components. Significantly, PMMA strand exchange was demonstrated and utilized to reversibly switch the micelles between different morphologies. This concept of strand exchange with PMMA-based triple-helix stereocomplexes offers new opportunities to program dynamic behaviors of polymeric materials, leading to scalable synthesis of "smart" nanosystems.

ABSTRACTThe synthesis and systematic comparison of a comprehensive library of well‐defined polymer architectures based on poly(acrylic acid) is reported. Through the development of new synthetic methodologies, linear, single branched, precision‐branched comb, and star polymers were prepared and their performance as dispersants was evaluated. The ability to accurately control chain lengths and branch points allows the subtle interplay between structure and dispersant performance to be defined and affords critical insights into the design of improved polymeric additives for coating formulations. The general industrial relevance of ionic polymers and branched macromolecular architectures supports these design rules for a wide range of other applications and materials, including as additives for personal care products and in water treatment. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 716–725

The triple-helix stereocomplex of poly(methyl methacrylate) (PMMA) is a unique example of a multistranded synthetic helix that has significant utility and promise in materials science and nanotechnology. To gain a fundamental understanding of the underlying assembly process, discrete stereoregular oligomer libraries were prepared by combining stereospecific polymerization techniques with automated flash chromatography purification. Stereocomplex assembly of these discrete building blocks enabled the identification of (1) the minimum degree of polymerization required for the stereocomplex formation and (2) the dependence of the helix crystallization mode on the length of assembling precursors. More significantly, our experiments resolved binding selectivity between helical strands with similar molecular weights. This presents new opportunities for the development of next-generation polymeric materials based on a triple-helix motif.

A practical and user-friendly strategy for the chain-end reduction of halogen terminated polymers that employs hydrogen gas and heterogeneous catalysis (palladium on carbon) is reported. Quantitative dehalogenation of a wide variety of monomer families (polystyrenes, polyacrylates, and polymethacrylates) with either chlorine or bromine chain-ends is observed. The utility of this chain-end reduction is further highlighted by mild reaction conditions, simple purification, and compatibility with a wide range of solvents.

A versatile strategy is reported for the multigram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, and siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multigram preparation of discrete oligomer libraries (Đ = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications.