Showing papers in "ACS Macro Letters in 2018"
TL;DR: Through better control of degradation behavior and correlation of in vitro, simulated degradation to that observed in vivo, the development of superior devices prepared with polyester biomaterials may be achieved.
Abstract: Strategies to refine the degradation behavior of polyester biomaterials, particularly to overcome the limitations of slow hydrolytic degradation, would broaden their utility. Herein, we examine the complexities of polyester degradation behavior, its assessment and strategies for refinement. The factors governing polyester degradation are strikingly complex. In addition to the half-life of the hydrolytically-labile bond, a series of interdependent material properties must be considered. Thus, methods used to characterize such material properties, both before and during degradation, must be carefully selected. Assessment of degradation behavior is further complicated by the variability of reported test protocols and the need for accelerated rather than real-time in vitro testing conditions. Ultimately, through better control of degradation behavior and correlation of in vitro, simulated degradation to that observed in vivo, the development of superior devices prepared with polyester biomaterials may be achieved.
228 citations
TL;DR: The magnitude of device-associated infections, the role of biofilm formation in human pathogenesis, and recent advances in antimicrobial and antifouling polymers, as well as current strategies employed in commercial devices for preventing infection are highlighted.
Abstract: Hospital-acquired infections arising from implanted polymeric medical devices continue to pose a significant challenge for medical professionals and patients. Often times, these infections arise from biofilm accumulation on the device, which is difficult to eradicate and usually requires antibiotic treatment and device removal. In response, significant efforts have been made to design functional polymeric devices or coatings that possess antimicrobial or antifouling properties that limit biofilm formation and subsequent infection by inhibiting or eliminating bacteria near the device surface or by limiting the initial attachment of proteins and bacteria. In this Viewpoint, we highlight the magnitude of device-associated infections, the role of biofilm formation in human pathogenesis, and recent advances in antimicrobial and antifouling polymers, as well as current strategies employed in commercial devices for preventing infection.
189 citations
TL;DR: In this paper, the robust mechanical properties of traditional thermosets are sacrificed in exchange for rapid and efficient reprocessability in cross-link polymer networks that are cross-linked by dynamic covalent bonds.
Abstract: Polymer networks that are cross-linked by dynamic covalent bonds often sacrifice the robust mechanical properties of traditional thermosets in exchange for rapid and efficient reprocessability. Pol...
139 citations
TL;DR: In this article, two kinds of zwitterionic copolymers with benzoxaborole and catechol pendant groups, respectively, were designed for 3D cell encapsulation.
Abstract: Boronic ester, one typical example of dynamic covalent bonds, has presented great potential to prepare self-healing hydrogels However, most of currently reported hydrogels based on boronic esters are formed at pH > 8, which impeded their further use in physiological conditions In this study, we designed two kinds of zwitterionic copolymers with benzoxaborole and catechol pendant groups, respectively Owing to the lower pKa value of benzoxaborole (72), gelation can happen easily at pH 74 PBS after mixing these two copolymers due to efficient formation of benzoxaborole-catechol complexations The resulting hydrogels exhibited excellent self-healing property as well as dual pH/sugar responsiveness due to the dynamic nature of boronic ester Moreover, benefiting from the cell membrane bioinspired 2-methacryloyloxyethyl phosphorylcholine (MPC)-based polymeric matrix, the hydrogel was further investigated for 3D cell encapsulation The combination of biocompatible zwitterionic polymers with dynamic benzoxab
135 citations
TL;DR: In this paper, reversible cross-links formed by conjugate addition with a Meldrum's acid derivative enable compression-remolding of silicone elastomers after 10 remolding cycles.
Abstract: Current vitrimer technology uses only a handful of distinct reactions for cross-linking. New dynamic reactions can diversify vitrimer functionality and properties. In this paper, reversible cross-links formed by conjugate addition–elimination of thiols with a Meldrum’s acid derivative enable compression–remolding of silicone elastomers. After 10 remolding cycles, there is no discernible deterioration of mechanical properties (Young’s modulus, Tg, rubbery plateau E’), nor is there a change in stress relaxation activation energy. This robust new cross-linker could be implemented in any number of systems that currently use permanent thiol–ene cross-linking, expanding the scope of recyclable materials.
129 citations
TL;DR: This work demonstrates the utility of self-healing materials for multi-dimensional cultures and establishes approaches broadly useful for a variety of biological applications.
Abstract: Synthetic hydrogels have been widely adopted as well-defined matrices for three-dimensional (3D) cell culture, with increasing interest in systems that enable the co-culture of multiple cell types for probing both cell–matrix and cell–cell interactions in studies of tissue regeneration and disease. We hypothesized that the unique dynamic covalent chemistry of self-healing hydrogels could be harnessed for not only the encapsulation and culture of human cells but also the subsequent construction of layered hydrogels for 3D co-cultures. To test this, we formed hydrogels using boronic acid-functionalized polymers and demonstrated their self-healing in the presence of physiologically relevant cell culture media. Two model human cell lines, MDA-MB-231 breast cancer cells and CCL151 pulmonary fibroblasts, were encapsulated within these dynamic materials, and good viability was observed over time. Finally, self-healing of cut hydrogel “blocks” laden with these different cell types was used to create layered hydro...
108 citations
TL;DR: In this article, the effect of catalyst strength on polyester-alcohol dynamic covalent exchange was systematically studied using Bronsted acids and a low-Tg poly(4-methylcaprolactone) vitrimer formulation.
Abstract: The effect of catalyst strength on polyester–alcohol dynamic covalent exchange was systematically studied using Bronsted acids and a low-Tg poly(4-methylcaprolactone) vitrimer formulation. Relaxation times, activation energies, and Arrhenius prefactors are correlated with pKa. Strong protic acids induce facile network relaxation at 25 °C on the order of 104–105 s, significantly faster than Lewis acid alternatives that function only above 100 °C. Activation energies span 49–67 kJ/mol and increase as pKa decreases. The opposite trend is observed with the Arrhenius prefactor. We anticipate that the quantitative understanding of Bronsted acid effects disclosed herein will be of utility in future studies that exploit acid-catalyzed dynamic covalent bond exchange.
107 citations
TL;DR: This work opened a new avenue for creating more complex architectures than 3D with excellent properties, which is important in the macromolecule fields for the wide applications.
Abstract: Hydrogels combined with complex 3D shapes and robust mechanical properties are extremely desired soft platforms in the fields of biomaterials, recently, 4D printing has been developed to be further shaped to form required patterns. On the basis of the excellent thixotropy of Laponite and the thermal-reversible sol–gel transition of agarose and easy formation of nanofibers below 35 °C, a 4D printing hydrogel (4D Gel) was fabricated by in situ polymerizing acrylamide in the agarose matrix containing Laponite. The experimental results demonstrated that Laponite played an important role in the improvement of 4D printing, such as endowing the ink with shear-thinning behavior to extrude easily and excellent shape stability after printing. The mechanical properties of 4D Gel were unexpectedly higher than those of both agarose and polyacrylamide hydrogels. The 4D Gel showed the ability to further transform its shapes, and was used successfully to construct a whalelike hydrogel, which opened mouth and cocked tail ...
104 citations
TL;DR: A new procedure for ultrasonication-induced atom transfer radical polymerization (sono-ATRP) in aqueous media was developed in this paper, which enabled polymerization of water-soluble monomers with excellent control over the molecular weight, dispersity, and high retention of chain-end functionality.
Abstract: A new procedure for ultrasonication-induced atom transfer radical polymerization (sono-ATRP) in aqueous media was developed Polymerizations of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) and 2-hydroxyethyl acrylate (HEA) in water were successfully carried out in the presence of ppm amounts of CuBr2 catalyst and tris(2-pyridylmethyl)amine ligand when exposed to ultrasonication (40 kHz, 110 W) at room temperature Aqueous sono-ATRP enabled polymerization of water-soluble monomers with excellent control over the molecular weight, dispersity, and high retention of chain-end functionality Temporal control over the polymer chain growth was demonstrated by switching the ultrasound on/off due to the regeneration of activators by hydroxyl radicals formed by ultrasonication The synthesis of a well-defined block copolymer and DNA–polymer biohybrid was also successful using this process
102 citations
TL;DR: It is shown that self-recovery hydrogels are still susceptible to fatigue fracture, and the threshold for fatigue fracture depends on the covalent network but negligibly on noncovalent interactions.
Abstract: Hydrogels of superior mechanical behavior are under intense development for many applications. Some of these hydrogels can recover their stress–stretch curves after many loading cycles. These hydrogels are called self-recovery hydrogels or even fatigue-free hydrogels. Such a hydrogel typically contains a covalent polymer network, together with some noncovalent, reversible interactions. Here we show that self-recovery hydrogels are still susceptible to fatigue fracture. We study a hydrogel containing both covalently cross-linked polyacrylamide and un-cross-linked poly(vinyl alcohol). For a sample without precut crack, the stress–stretch curve recovers after thousands of loading cycles. For a sample with a precut crack, however, the crack extends cycle by cycle. The threshold for fatigue fracture depends on the covalent network but negligibly on noncovalent interactions. Above the threshold, the noncovalent interactions slow down the extension of the crack under cyclic loads.
101 citations
TL;DR: It is demonstrated that the [2 + 2] photocycloaddition of styrylpyrene can be activated by visible light at λ = 400-500 nm, enabling rapid and effective conjugation and cross-linking of poly(ethylene glycol) (PEG) in water and under mild irradiation conditions.
Abstract: Reversible photocycloaddition reactions have previously been employed in chemical cross-linking for the preparation of biomaterial scaffolds. However, the processes require activation by high-energy UV light, rendering them unsuitable for modification in biological environments. Here we demonstrate that the [2 + 2] photocycloaddition of styrylpyrene can be activated by visible light at λ = 400–500 nm, enabling rapid and effective conjugation and cross-linking of poly(ethylene glycol) (PEG) in water and under mild irradiation conditions (I = 20 mW cm–2). Notably, the reversion of the cycloaddition can be triggered by low-energy UV light at λ = 340 nm, which allows for efficient cleavage of the dimer adduct. Using this wavelength-gated reversible photochemical reaction we are able to prepare PEG hydrogels and modulate their mechanical properties in a bidirectional manner. We also demonstrate healing of the fractured hydrogel by external light triggers. Furthermore, we show that human mesenchymal stem cells ...
TL;DR: In this paper, the linear viscoelastic behavior of poly(norbornene)-graft-poly(±-lactide) was investigated as a function of grafting density and overall molar mass.
Abstract: The linear viscoelastic behavior of poly(norbornene)-graft-poly(±-lactide) was investigated as a function of grafting density and overall molar mass. Eight sets of polymers with grafting densities ranging from 0 to 100% were synthesized by living ring-opening metathesis copolymerization. Within each set, the graft chain molar mass and spacing between grafts were fixed, while the total backbone length was varied. Dynamic master curves reveal that these polymers display Rouse and reptation dynamics with a sharp transition in the zero-shear viscosity data, demonstrating that grafting density strongly impacts the entanglement molar mass. The entanglement modulus (Ge) scales with inverse grafting density (ng) as Ge ∼ ng1.2 and Ge ∼ ng0 in accordance with scaling theory in the high and low grafting density limits, respectively. However, a sharp transition between these limiting behaviors occurs, which does not conform to existing theoretical models for graft polymers. A molecular interpretation based on thin fl...
TL;DR: The synthesis of a novel antimicrobial/antibiofilm polymer that consists of biocompatible oligoethylene glycol, hydrophobic ethylhexyl, cationic primary amine, and nitric oxide-releasing functional groups has dual-action capability as it can release NO which triggers the dispersion of biofilm, whereas the polymer can induce bacteria cell death via membrane wall disruption.
Abstract: Bacterial biofilms are often difficult to treat and represent the main cause of chronic and recurrent infections. In this study, we report the synthesis of a novel antimicrobial/antibiofilm polymer that consists of biocompatible oligoethylene glycol, hydrophobic ethylhexyl, cationic primary amine, and nitric oxide (NO)-releasing functional groups. The NO-loaded polymer has dual-action capability as it can release NO which triggers the dispersion of biofilm, whereas the polymer can induce bacteria cell death via membrane wall disruption. By functionalizing the polymers with NO, we observed a synergistic effect in biofilm dispersal, planktonic and biofilm killing activities against Pseudomonas aeruginosa. The NO-loaded polymer results in 80% reduction in biofilm biomass and kills >99.999% of planktonic and biofilm P. aeruginosa cells within 1 h of treatment at a polymer concentration of 64 μg mL–1. To achieve this synergistic effect, it is imperative that the NO donors and antimicrobial polymer exist as a s...
TL;DR: In this paper, the effect of salt on segmental dynamics in polymers was quantified in the 1-10-A length scale and it was shown that the change in monomeric friction alone is responsible for all of the observed nonlinearity in the dependence of ionic conductivity on salt concentration.
Abstract: Quasi-elastic neutron scattering experiments on mixtures of poly(ethylene oxide) and lithium bis(trifluoromethane)sulfonimide salt, a standard polymer electrolyte, led to the quantification of the effect of salt on segmental dynamics in the 1–10 A length scale. The monomeric friction coefficient characterizing segmental dynamics on these length scales increases exponentially with salt concentration. More importantly, we find that this change in monomeric friction alone is responsible for all of the observed nonlinearity in the dependence of ionic conductivity on salt concentration. Our analysis leads to a surprisingly simple relationship between macroscopic ion transport in polymers and dynamics at monomeric length scales.
TL;DR: DFT calculations provide insights into the origins of ferrocene's mechanical lability by revealing that the Fe-Cp bond is similar in strength to the carbon-nitrogen bond of an azobisdialkylnitrile (bond dissociation energy < -0 kcal/mol).
Abstract: Ferrocene is classically regarded as being highly inert owing to the large dissociation energy of metal-cyclopentadienyl (Cp) bonds We show that the Fe-Cp bond in ferrocene is the preferential site of mechanochemical scission in the pulsed ultrasonication of main-chain ferrocene-containing polybutadiene-derived polymers Quantitative studies reveal that the Fe-Cp bond is similar in strength to the carbon-nitrogen bond of an azobisdialkylnitrile (bond dissociation energy < -0 kcal/mol), despite the significantly higher Fe-Cp bond dissociation energy (approximately 90 kcal/mol) Mechanistic studies are consistent with a predominately heterolytic mechanism of chain scission DFT calculations provide insights into the origins of ferrocene's mechanical lability
TL;DR: In this article, a series of poly(anthraquinonyl sulfides) polymers with different polysulfide segment lengths (x between 2 and 9 sulfur atoms) have been synthesized in high yields by reacting in situ formed sodium polypolysulfides with 1,5-dicholoro anthraquinone.
Abstract: Redox polymers with high energy storage capacity are searched in order to diminish the weight to the actual batteries. Poly(anthraquinonyl sulfide) PAQS is a popular redox polymer which has shown a high performance cathode for lithium, sodium and magnesium batteries. Although PAQS cathodes show high cycling stability it has a relatively low theoretical specific capacity of 225 mAh/g. In this paper we show the synthesis and characterization of new poly(anthraquinonyl sulfides) PAQxS in an attempt to improve the specific capacity of PAQS. Thus, a series of PAQxS polymers with different polysulfide segment lengths (x between 2 and 9 sulfur atoms) have been synthesized in high yields by reacting in situ formed sodium polysulfides with 1,5-dicholoroanthraquinone. The poly(anthraquinonyl sulfides) powders were characterized by ATR-FTIR, solid state 13C NMR for the organic part and Raman spectroscopy for the chalcogenide part. This characterization confirmed the chemical structure of the PAQxS based on an anthra...
TL;DR: In this article, the effect of the polarity of the polymer electrolyte on ion mobilities and conductivities of dissolved salts was investigated using coarse-grained molecular dynamics simulations.
Abstract: In this work, we use computer simulations to demonstrate that there may be limits to which polymer polarity alone can be used to influence the ionic conductivity of salt-doped polymer electrolytes. Specifically, we use coarse-grained molecular dynamics simulations to probe the effect of the polarity of the polymer electrolyte upon ion mobilities and conductivities of dissolved salts. At low polymer polarities, increasing the polymer dielectric constant reduces ionic aggregation and the resultant correlated ionic motion, and increases the ionic conductivity. At higher polymer polarities, polymer–polymer and polymer–ion interactions slows polymer segmental dynamics, leading to a reduction in the conductivity of the electrolyte. As a consequence, ionic conductivity achieves an optimum at an intermediate polymer polarity.
TL;DR: In this article, the authors report their preliminary findings on multicolor mechanochromic polymer blends that can discriminate between two different mechanical stimuli, i.e., stretching and grinding.
Abstract: Mechanochromic polymers, which react to mechanical force by changing color, are expected to find applications in smart materials such as damage sensors. Although numerous types of mechanochromic polymers have been reported so far, developing mechanochromic polymers that can recognize different mechanical stimuli remains a formidable challenge. Materials that not only change their color in response to a mechanical stimulus but also detect its nature should be of great importance for practical applications. In this paper, we report our preliminary findings on multicolor mechanochromic polymer blends that can discriminate between two different mechanical stimuli, i.e., stretching and grinding, by simply blending two mechanochromic polymers with different architectures. The rational design and blending of two mechanochromic polymers with radical-type mechanochromophores embedded separately in positions adjacent to soft or hard domains made it possible to achieve multicolor mechanochromism in response to diffe...
TL;DR: In this paper, the effect of tie-chain connectivity on the electrical properties of polyolefins was quantitatively evaluated using the Huang-Brown model, a framework commonly used to describe the structural origins of mechanical properties.
Abstract: Intercrystallite molecular connections are widely recognized to tremendously impact the macroscopic properties of semicrystalline polymers. Because it is challenging to directly probe such connections, theoretical frameworks have been developed to quantify their concentrations and predict the mechanical properties that result from these connections. Tie-chain connectivity similarly impacts the electrical properties in semicrystalline conjugated polymers. Yet, its quantitative impact has eluded the community. Here, we assess the Huang–Brown model, a framework commonly used to describe the structural origins of mechanical properties in polyolefins, to quantitatively elucidate the effect of tie chains on the electrical properties of a model conjugated polymer. We found that a critical tie-chain fraction of 10–3 is needed to support macroscopic charge transport, below which intercrystallite connectivity limits charge transport, and above which intracrystallite disorder is the bottleneck. Extending the Huang–B...
TL;DR: N,N-Diaryl dihydrophenazines are employed as organic photoredox catalysts (PCs) for photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization to perform a sequential PET-RAFT/O-ATRP block copolymerization of PMA-b-PMMA using the same PC for both polymerizations.
Abstract: N,N-Diaryl dihydrophenazines are employed as organic photoredox catalysts (PCs) for photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The ability of these PCs to mediate PET-RAFT is heavily dependent on the ability of the PC to access a photoexcited intramolecular charge transfer state. The use of PCs displaying intramolecular charge transfer in the excited state allows for efficient PET-RAFT of a variety of monomers, including vinyl acetate, and in a wide range of solvents. The ability of these PCs to also mediate organocatalyzed atom transfer radical polymerization (O-ATRP) is exploited to perform a sequential PET-RAFT/O-ATRP block copolymerization of PMA-b-PMMA using the same PC for both polymerizations.
TL;DR: In this article, a facile bench-top process for the synthesis of cross-linked polymeric nanoparticles by exploiting wavelength-selective photochemistry to perform orthogonal photoinduced polymerization is described.
Abstract: We report a facile benchtop process for the synthesis of cross-linked polymeric nanoparticles by exploiting wavelength-selective photochemistry to perform orthogonal photoinduced polymerization-ind...
TL;DR: The facile addition of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to commercially available poly(4,4′-oxydiphenylene pyromellitamic acid) (PMDA-ODA PAA) provided ultraviolet curable PAA salt solutions as discussed by the authors.
Abstract: Polyamic acid (PAA) salts are amenable to photocuring additive manufacturing processes of all-aromatic polyimides. Due to an all-aromatic structure, these high-performance polymers are exceptionally chemically and thermally stable but are not conventionally processable in their imidized form. The facile addition of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to commercially available poly(4,4′-oxydiphenylene pyromellitamic acid) (PMDA-ODA PAA) afforded ultraviolet curable PAA salt solutions. These readily prepared solutions do not require multistep synthesis, exhibited fast gel times (<5 s), and rendered high G′ gel-state moduli. Vat photopolymerization 3D printing afforded self-supporting organogels. Subsequent thermal treatment rendered the cross-linked PAA precursor to all-aromatic PMDA-ODA polyimide. This fast and facile strategy makes PMDA-ODA polyimides accessible in three dimensions and offers impact on aerospace or automotive technologies.
TL;DR: In this article, the transport of penetrants through nanoscale morphologies motivated by common block copolymer morphologies was studied using confined random walks and coarse-grained simulations.
Abstract: We study transport of penetrants through nanoscale morphologies motivated by common block copolymer morphologies, using confined random walks and coarse-grained simulations Diffusion through rando
TL;DR: In this paper, the authors demonstrate that cyclic trimeric phosphazene base (CTPB) can catalyze stereoselective ring-opening polymerization of rac-lactide (rac-LA) to produce isotactic stereoblock PLA (Pi up to 0.93).
Abstract: Phosphazene base is an important organocatalyst in polymer chemistry owing to its high activity and versatility. In this contribution, we demonstrate that cyclic trimeric phosphazene base (CTPB) can catalyze stereoselective ring-opening polymerization (ROP) of rac-lactide (rac-LA) to produce isotactic stereoblock PLA (Pi up to 0.93). The polymerizations are highly controlled, as evidenced by linear relationship between molecular weights (MW) and monomer conversions and the narrow dispersity (Đ = Mw/Mn) of the resulted polymers with high fidelity of end groups. The investigations on polymerization parameters show that the tacticity of produced PLA depends on the polymerization temperatures and solvents, while the kinetic studies reveal a faster rate for ROP of l-LA as compared to rac-LA under same conditions. Based on these results, the chain end control mechanism is proposed to explain the production of isotactic stereoblock PLA from rac-LA by an achiral catalyst.
TL;DR: In this paper, an efficient route to the preparation of anisotropic morphologies of azobenzene-containing block copolymers (BCPs) at high solids content via a polymerization-induced hierarchical self-assembly in ethanol is presented.
Abstract: Polymeric nanoparticles (NPs) containing liquid crystalline (LC) mesogens with tunable anisotropic morphologies have applications in various fields, but their preparation typically suffers from tedious and low-throughput approaches. Here we present an efficient route to the preparation of anisotropic morphologies of azobenzene-containing block copolymers (BCPs) at high solids content via a polymerization-induced hierarchical self-assembly in ethanol. Various anisotropic NPs, including cuboids, short belts, lamellae, and ellipsoidal vesicles, have been obtained in a remarkably broad range of BCP compositions. The NPs exhibit a smectic phase with ordered stripes when observed under TEM. This internal LC ordering plays a significant role on the formation of these intriguing anisotropic morphologies. Morphological transitions from anisotropic to isotropic spheres can be obtained upon UV illumination due to the photoresponsive properties of the azobenzene mesogens. This work significantly expands the scope of ...
TL;DR: In this article, a left-handed helical poly (phenyl isocyanide) bearing a norbornene unit and a Pd(II) complex on each terminus was prepared.
Abstract: A left-handed helical poly(phenyl isocyanide) bearing a norbornene unit and a Pd(II) complex on each terminus was prepared. The norbornene terminus was core cross-linked with a bisnorbornene linker via ring-opening metathesis polymerization (ROMP), yielding a star polymer carrying left-handed helical arms decorated with Pd(II) units at the exterior. The optical activities of the helical arms were maintained after the cross-linking reaction. The Pd(II) units on the surface of the star polymer were chain extended with a new phenyl isocyanide bearing three hydrophilic triethylene glycol monomethyl chains, which afforded an amphiphilic star block copolymer carrying helical arms. Such a star block copolymer showed excellent thermoresponsiveness with the lower critical solution temperature (LCST) around 55 °C. This optically active and thermoresponsive star polymer can enantioselectively capture the S-enantiomer of racemic methyl benzyl alcohol solution at a temperature lower than the LCST and precipitated when...
TL;DR: In this article, the thermal conductivity of liquid crystalline epoxy resin (LCER) was improved by replacing the conventional amine crosslinker with a cationic initiator.
Abstract: A powerful strategy to enhance the thermal conductivity of liquid crystalline epoxy resin (LCER) by simply replacing the conventional amine cross-linker with a cationic initiator was developed. The...
TL;DR: In this article, the basic principles underlying optical tweezers microrheology, the instrumentation and material requirements, and key applications to widely studied soft biological materials are described.
Abstract: Over the past few decades, microrheology has emerged as a widely used technique to measure the mechanical properties of soft viscoelastic materials. Optical tweezers offer a powerful platform for performing microrheology measurements and can measure rheological properties at the level of single molecules out to near macroscopic scales. Unlike passive microrheology methods, which use diffusing microspheres to extract rheological properties, optical tweezers can probe the nonlinear viscoelastic response, and measure the space- and time-dependent rheological properties of heterogeneous, nonequilibrium materials. In this Viewpoint, I describe the basic principles underlying optical tweezers microrheology, the instrumentation and material requirements, and key applications to widely studied soft biological materials. I also describe several sophisticated approaches that include coupling optical tweezers to fluorescence microscopy and microfluidics. The described techniques can robustly characterize noncontinuu...
TL;DR: A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, that is, [κ2-P,O-(R12P)CH2P(O)R22]PdMe(2,6-lutidine)][BArF4] (Pd/BPMO), were synthesized and evaluated as catalysts for the homopolymerization of ethylene and the copolymerisation of polyethylene and polar monomers.
Abstract: A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, that is, [κ2-P,O-(R12P)CH2P(O)R22]PdMe(2,6-lutidine)][BArF4] (Pd/BPMO), were synthesized and evaluated as catalysts for the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. X-ray crystallographic analyses revealed that these Pd/BPMO complexes exhibit significantly narrower bite angles and longer Pd–O bonds than Pd/BPMO complexes bearing a phenylene linker, while maintaining almost constant Pd–P bond lengths. Among the complexes synthesized, menthyl-substituted complex 3f (R1 = (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-yl; R2 = Me) showed the best catalytic performance in the homo- and copolymerization in terms of molecular weight and polymerization activity. Meanwhile, complex 3e (R1 = t-Bu; R2 = Me) exhibited a markedly higher incorporation of comonomers in the copolymerization of ethylene and allyl acetate (≤12.0 mol %) or methyl methacrylate (≤0.6 mol %). The catalytic syste...
TL;DR: Aqueous-phase ring-opening metathesis polymerization-induced self-assembly (ROMPISA) was used in this paper for forming micellar polymer nanoparticles at room temperature and high solids concentration.
Abstract: We report aqueous-phase Ring-Opening Metathesis Polymerization-Induced Self-Assembly (ROMPISA) for forming well-defined micellar polymer nanoparticles at room temperature and high solids concentration (20 w/w%). This is achieved with a new polymerization initiator, in the form of a water-soluble cationic Hoveyda-Grubbs second generation catalyst. This reaction was used in water to produce diblock copolymers from norbornenyl monomers, which then self-assemble into myriad nanostructure morphologies for which a phase diagram was constructed. Additionally, the living nature of the polymerization initiated by the aqueous initiator was confirmed, as shown by kinetic evaluation under mild conditions in water.