Fused filament fabrication offers the ability to 3D print complex geometries made from plastic filament materials; however, these parts are mechanically outperformed by parts created by traditional fabrication methods. To overcome this challenge, a high-performance polymer poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is incorporated as an additive into two common engineering thermoplastics, poly(acrylonitrile-styrene-acrylate) (ASA) and poly(acrylonitrile-butadiene-styrene) (ABS). Structures printed from these polymer blends are more mechanically robust compared to those prepared from the parent polymers, with low loading levels (1-5 wt%) of PPO improving the elastic strength by up to approximate to 30% relative to the parent terpolymers. Even at higher loading levels (10 and 20 wt% PPO), there is no evidence of additive aggregation in the model thin films, which is supported by compositional analysis of the copolymers and chemical analysis via time-of-flight secondary ion mass spectrometry. The enhancements in mechanical properties of ASA and ABS blends appear to be a consequence of homogeneous incorporation of the PPO additive. This work explores expanding materials-property space using miscible blends of engineering thermoplastics to improve mechanical performance as a general approach to overcoming challenges with parts created by melt-based material extrusion printing.

Conjugated polymers are promising materials for organic electronic devices; however, to achieve metal-like electrical properties, these materials need to be chemically doped. In this work, a series of structurally tailored thiophene-based copolymers are studied to elucidate relationships between copolymer design, doping method, solubility, and electrical conductivity. The results show that increasing the distance between side chains along the conjugated backbone increases thin film conductivity, with conductivities surpassing that of poly(3-hexylthiophene) (P3HT) by several orders of magnitude for solution and sequential doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). In addition, the conductivities of films subjected to sequential doping show a dependence on the polymer-solvent interaction energy, which appears universal for this series of thiophene-based copolymers, offering a potentially predictive basis for choosing an optimal solvent for doping. These studies also show that sequential doping provides higher thin film conductivity at lower concentrations of anionic F4TCNQ. This indicates that sequential doping is superior in that less dopant is necessary to achieve the same, if not greater, electrical performance for these thiophene-based copolymers. Overall, this work provides fundamental insight into how copolymer design, doping method, and strength of polymer-solvent interaction energy impact electrical performance, paving the way for printed electronics, sensors, and other applications for chemically doped conjugated polymers.

Polyolefins, which dominate the plastics marketplace, require high-temperature size exclusion chromatography (HT-SEC) to characterize their molar masses. Chemical recycling methods designed to deconstruct plastic waste into smaller molecules (i.e., depolymerization methods) rely on HT-SEC to characterize their products, but depolymerization methods often yield a complex mixture, including components below the typical separation range of commercial HT-SEC columns. Herein, we report the accuracy and limitations of triple detection HT-SEC to analyze model chemical recycling products. We examined the chromatographic separation and quantification of individual components and mixtures of short polyethylenes (apparent M n = 465 and 2722 g/mol), hexatriacontane (C36H74, M = 507 g/mol), dotriacontane (C32H66, M = 451 g/mol), and octadecane (C18H38, M = 254 g/mol). Despite short alkanes exhibiting molar masses below the lower molar mass limit of the columns (500 g/mol), the separation of their mixtures was resolved via refractive index (RI) detection. However, the determined molar masses of these alkane mixtures did not agree with the known molar masses of the short alkanes or their prepared mixtures. Similarly, the SEC analysis of mixtures containing discrete alkanes with low molar mass PE revealed that their individual components are easily resolved in the HT-SEC chromatogram. No obvious shift in the elution volume of the blend components versus the elution volume of the pure components was observed. However, inaccurate molar masses and molar mass distributions for these alkane-PE mixtures are calculated from the HT-SEC data. These inaccuracies are attributable to two factors: (1) molar mass-dependent ∂n/∂c for low molar mass components and (2) the small size of the molecules in solution that limits light scattering. These results highlight the importance of considering measurement limitations for quantitative interpretation of triple detection HT-SEC data obtained from chemical recycling and depolymerization experiments that commonly contain complex mixtures of polymeric, oligomeric, and small molecule alkanes.

Polymeric materials containing amidine motifs are of high interest due to their ability to reversibly capture and release CO2 at ambient temperature. Here we probe physical and chemical responses of styrene-based copolymers containing linear amidine motifs as functions of CO2 and inert gas exposures and temperature. A copper-catalyzed azide-alkyne cycloaddition "click" reaction involving N '-propargyl-N,N-dimethylacetamidine is used to modify random copolymers, resulting in an array of linear amidine motifs along the chain backbone with the amount of CO2-active amidine controlled by the copolymer composition. Through thermogravimetric measurements, we demonstrate that the amidine-functionalized copolymers efficiently capture CO2 upon exposure to a stream of CO2 (at 27 degrees C) and release it at a slightly elevated temperature (50 degrees C) when exposed to an inert gas stream (N2). In addition to displaying a maximum adsorption capacity of 22 wt % in the presence of pure CO2, the copolymers show composition-dependent direct air capture (DAC) behaviors. Small molecule analogs are used to definitively understand degradation via chemical hydrolysis of the amidine moiety, which leads to insolubility and a large reduction in CO2 adsorption capacity (1.7 wt %). Neutron vibrational spectroscopy and DFT calculations confirm that CO2 binds strongly to the amidine motif, inducing a strong bending of the CO2 molecule from its linear geometry. The coupled insights into mechanisms and behaviors of CO2 adsorption in amidine-functionalized polymers provides a foundation for future investigations of CO2-responsive polymers and soft materials to improve carbon capture and sequestration technologies.

Piezo- and pyroelectric materials are of interest, for example, for energy harvesting applications, for the development of tactile sensors, as well as neuromorphic computing. This study reports the observation of pyro- and piezoelectricity in thin surface-attached polymer brushes containing zwitterionic and electrolytic side groups that are prepared via surface-initiated polymerization. The pyro- and piezoelectric properties of the surface-grafted polyelectrolyte brushes are found to sensitively depend on and can be tuned by variation of the counterion. The observed piezo- and pyroelectric properties reflect the structural complexity of polymer brushes, and are attributed to a complex interplay of the non-uniform segment density within these films, together with a non-uniform distribution of counterions and specific ion effects. The fabrication of thin pyroelectric films by surface-initiated polymerization is an important addition to the existing strategies toward such materials. Surface-initiated polymerization, in particular, allows for facile grafting of polar thin polymer films from a wide range of substrates via a straightforward two-step protocol that obviates the need for multistep laborious synthetic procedures or thin film deposition protocols. The ability to produce polymer brushes with piezo- and pyroelectric properties opens up new avenues of application of these materials, for example, in energy harvesting or biosensing.

The addition of nanoparticles or copolymer grafted nanoparticles (CPGNPs) to polymeric matrices greatly im-proves thermomechanical properties of the resulting nanocomposite, but corresponding studies of nano -composite systems created by 3D printing are few, especially in the realm of functional polymeric materials. Here we describe how silica nanoparticle-grafted, random copolymers of poly(methyl methacrylate-random-2-uriedo-[1H]-pyrimidinone methacrylate) (P(MMA-r-UPyMA) dramatically increases the mechanical properties of poly (methyl methacrylate) (PMMA) based nanocomposite specimens created by melt extrusion printing. Most notably, when these novel CPGNPs are combined with PMMA matrix chains via a solution-based process, printed specimens containing only 0.5 wt% additive show significant increases in Young's modulus (90%), storage modulus (93%), tensile modulus (148%) and ultimate tensile strength (110%). These improvements are ascribed to strengthening of adhesion across interfaces due to multi-point hydrogen bonding between UPyMA groups, the reinforcement effect of the P(MMA-r-UPyMA)-grafted silica nanoparticles, as well as hydrogen bonding in-teractions and entanglements between graft and matrix chains. Imaging of fracture surfaces after tensile testing reveals that in comparison to nanocomposites created by simple mechanical mixing of solids, the solution-casting process improves the dispersion of nanoparticles and reduces the void spaces between printed beads. These studies demonstrate that introducing functionality into polymer grafts, such as hydrogen bonding interactions, and intimate mixing of polymer-modified nanomaterials can greatly improve interlayer adhesion and mechanical properties, thereby advancing this method of polymer additive manufacturing.

The most effective antifouling coatings are designed to slowly release biocides that target a broad spectrum of marine organisms. However, as biocides have a deleterious effect on marine life, there is demand for environmentally friendly coatings that resist fouling through physical interactions. We propose a simple platform for the development of such coatings based on bottlebrush-modified elastomers. The bottlebrush additives were synthesized to have side chain chemistries that are known to be fouling-resistant, and these were incorporated in a commercial elastomer through blending and/or covalent attachment. The fouling performance of these coatings was highly variable, with area coverages of hard and soft foulants ranging from 1.4% to 7.2% and 29.1% to 64.0%, respectively, across a set of eight materials. The origin of these differences was explained by examining the structure of the coating surface through chemical imaging by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and topographic imaging by atomic force microscopy (AFM). We found that fouling by certain soft and hard fouling organisms was primarily influenced by surface composition, which was controlled by both the chemistry and loading level of the bottlebrush additive, and was independent of the inherent surface roughness. While no type of coating could resist all soft and hard foulants, a formulation based on a bottlebrush copolymer additive with both siloxane and fluorinated monomers was effective against nearly all organisms encountered in the study.

Block copolymer (BCP) thermoplastics are used in a wide range of commercial products. It is well known that the mechanical performance of these materials depends on the BCP architecture and composition, and the introduction of non-covalent interactions via comonomers can be used to tune key properties. However, tailoring the mechanics of BCPs by blending with polymeric additives is rarely explored, as most BCP/polymer blends have limited miscibility. Here, we examine the structure, mechanics, and thermal stability of a commodity thermoplastic, poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS), with polymeric additives of either polystyrene (PS) or poly(methyl methacrylate-co-cyclohexyl methacrylate) (PrC, 70 mol % cyclohexyl methacrylate). PS and PrC are athermal and enthalpically compatible additives, respectively, for the PS end-blocks in SEBS. The SEBS/PS blends have a narrow miscibility window with respect to PS molecular weight and loading, where either an ordered lamellar morphology or a disordered morphology is observed. In contrast, the attractive interaction between PrC and PS end-blocks leads to complete miscibility of SEBS/PrC blends across the full range of PrC molecular weights (up to 63.8 kg/mol) and loadings (up to 40 vol %) that were studied, where an ordered lamellar morphology with continuity in the rubber phase was generally observed. Consequently, the PrC additives can increase the modulus and yield stress, as well as delay the onset of strain hardening, without loss of toughness. Additionally, PrC additives can elevate the glass transition temperature of the PS blocks and maintain a high modulus at elevated operating temperatures, expanding the service window for SEBS. The principles established in this research could be translated to other types of styrenic BCP thermoplastics.

The Quite Intense Kinetics Reflectometer (QIKR) will be a general-purpose, horizontal-sample-surface neutron reflectometer. Reflectometers measure the proportion of an incident probe beam reflected from a surface as a function of wavevector (momentum) transfer to infer the distribution and composition of matter near an interface. The unique scattering properties of neutrons make this technique especially useful in the study of soft matter, biomaterials, and materials used in energy storage. Exploiting the increased brilliance of the Spallation Neutron Source Second Target Station, QIKR will collect specular and off-specular reflectivity data faster than the best existing such machines. It will often be possible to collect complete specular reflectivity curves using a single instrument setting, enabling "cinematic" operation, wherein the user turns on the instrument and "films" the sample. Samples in time-dependent environments (e.g., temperature, electrochemical, or undergoing chemical alteration) will be observed in real time, in favorable cases with frame rates as fast as 1 Hz. Cinematic data acquisition promises to make time-dependent measurements routine, with time resolution specified during post-experiment data analysis. This capability will be deployed to observe such processes as in situ polymer diffusion, battery electrode charge-discharge cycles, hysteresis loops, and membrane protein insertion into lipid layers.

Conjugated copolymers containing electron donor and acceptor units in their main chain have emerged as promising materials for organic electronic devices due to their tunable optoelectronic properties.

Chain exchange behaviors in self-assembled block copolymer (BCP) nanoparticles (NPs) at room temperature are investigated through observations of structural differences between parent and binary systems of BCP NPs with and without crosslinked domains. Pairs of linear diblock or triblock, and branched star-like polystyrene-poly(2-vinylpyridine) (PS-PVP) copolymers that self-assemble in a PVP-selective mixed solvent into BCP NPs with definite differences in size and self-assembled morphology are combined by diverse mixing protocols and at different crosslinking densities to reveal the impact of chain exchange between BCP NPs. Clear structural evolution is observed by dynamic light scattering and AFM and TEM imaging, especially in a blend of triblock + star copolymer BCP NPs. The changes are ascribed to the chain motion inherent in the dynamic equilibrium, which drives the system to a new structure, even at room temperature. Chemical crosslinking of PVP corona blocks suppresses chain exchange between the BCP NPs and freezes the nanostructures at a copolymer crosslinking density (CLD) of ∼9%. This investigation of chain exchange behaviors in BCP NPs having architectural and compositional complexity and the ability to moderate chain motion through tailoring the CLD is expected to be valuable for understanding the dynamic nature of BCP self-assemblies and diversifying the self-assembled structures adopted by these systems. These efforts may guide the rational construction of novel polymer NPs for potential use, for example, as drug delivery platforms and nanoreactors.

The functionalizationPolymer nanocomposites of nanoparticlesNanoparticle has been broached as a possible means to ensuring their dispersionDispersion in polymer nanocompositesNanocomposites. We seek to draw a dynamic distinction between composites with “bare” nanoparticles and those with polymer-grafted nanoparticlesNanoparticle. For clarity, the former and latter systems are referred to simply as polymer nanocompositesPolymer nanocomposites (PNCs) and polymer-grafted nanocomposites (PGNCs), respectively. FurtherNanoparticle, we explore dynamicsDynamics in self-suspended nanoparticle organic hybrid materials (NOHMs) which retain liquid-like character.

Nanocomposites represent an important way to expand the boundaries of material-property space. To advance their use in printing by fused filament fabrication (FFF), we develop a method based on colloidal solution mixing to improve dispersion of various nanofiller additives in printed parts. Printed nanocomposites exhibit increases in Young’s modulus of up to 41%, decreases in part-to-part variation, and the ability to reach higher nanofiller loading levels. Optical microscopy shows a reduction in nanofiller aggregates in parts created using this solution casting method. Improvements in printability, quality, and performance of FFF-printed parts may accelerate the utility of nanocomposites in FFF.

AbstractWe present how altering the chain flexibility affects the nanoscale organization of polymer‐grafted nanoparticles (PGNPs) and its ultimate impact on macroscale thermal properties. To isolate the role of chain flexibility on wetting behavior in athermal polymer nanocomposites (PNC), the graft and matrix chemistry is kept identical by utilizing 1,3‐cyclohexadiene‐based polymer materials. Increasing the rigidity and molecular weight of both the graft and matrix is found to favor mixing of poly(1,3‐cyclohexadiene) PCHD‐grafted silica NPs with the matrix, supported by a concomitant increase in glass transition temperatures of the PNCs. Further, the associated entropic factors that drive wetting behavior and dispersion of PGNPs are discussed, emphasizing the dominant role‐played by chain flexibility. Alterations in graft flexibility had the strongest impact on dispersion and Tg values of the PNC, while molecular weight (MW) plays a secondary role. This investigation is a unique demonstration of how chain flexibility alteration in athermal semiflexible systems can be used to alter NP organization by altering filler‐matrix wettability which also impacts thermal properties.

A facile alkali sterilization strategy without any heat input makes lignin dispersion no longer a bottleneck limiting biological lignin valorization.

We use broad-band dielectric spectroscopy (BDS) and small-angle X-ray scattering (SAXS) to investigate the impact of architectural asymmetry in the miktoarm star copolymer on the dielectric polymer relaxations. The miktoarm copolymers studied contain one or two polystyrene (PS) chains of constant molecular weight and two identical poly(cis-1,4-isoprene) (PI) chains with varied molecular weights. Using the chains in the PI block as dielectric probes, we find that the architecturally asymmetric miktoarm star copolymer systems (PSPI2) feature distributions in chain relaxation times and dielectric relaxation strengths that are not dependent on molecular weight or morphology, in stark contrast to the effects of morphological confinement observed for symmetric diblock systems (PS-b-PI or PS2PI2). Along with evidence from the SAXS measurements regarding phase separation, these results are attributed to influences from chain stretching within the framework of the Gaussian chain model for block copolymer systems. As such, the molecular architecture in block copolymers happens to be a versatile handle to control polymer chain dynamics and, ultimately, the macroscopic physicochemical properties in architecturally complex polymers.

Direct arylation polymerization (DArP) has emerged as an environmentally friendly, atom efficient method of synthesizing a variety of conjugated polymers. Here, we report a one-pot approach consisting of DArP followed by Boc deprotection to synthesize a functional, surface-active adenine-containing poly(alkylthiophene). Careful control over the polymerization temperature enables the one-pot polymerization and deprotection strategy for synthesis, with quantitative (>99%) Boc deprotection achieved in 24 h. This temperature-controlled synthesis method reduces extra purification and isolation steps, which makes the total synthesis more efficient and practical, and allows higher molecular weight polymer to be made. We quantify the hydrogen bonding ability of the resulting adenine-containing polythiophene, T-Ad-tT(4h), by H-1 NMR host-guest titration studies and analyze the results with the Benesi-Hildebrand model, yielding an association constant of 18.7 M-1 between alkylated thymine and T-Ad-tT(4h). We demonstrate that T-Ad-tT(4h) robustly modifies the surface of cellulosic filter paper (CFP), and the modified cellulosic filter paper, CFP-T-Ad-tT(4h), is an effective oil-water separatory filter with superhydrophobic properties (water contact angle (CA) similar to 151 degrees). The utility of hydrogen bonding interactions between adenine and cellulose highlights the importance of side-chain engineering for creating functional materials.

Polymers exhibit deviations from their bulk physical properties in the vicinity of solid interfaces due to changes in configurations, entanglements, and relaxation dynamics at the interfacial regions. By comparing grafted and nongrafted polymer nanocomposite systems based on poly(methyl methacrylate) and silica, we show that the distribution of relaxation times exhibits both commonly reported slower mobility and faster modes that depend on the nature of the interfacial zone, matrix molecular weight, and loading level of nanomaterials. These findings are derived from studies using broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC) to probe molecular and interfacial dynamics. By systematically examining nanocomposites based on nonfunctionalized "bare" Si nanoparticles (NPs) dispersed in PMMA matrices and on PMMA-grafted Si NPs (PMMA-g-NPs) in PMMA matrices, we probe the effects of interfacial interactions and confinement in each of these cases on the glass transition temperature, T-g, the mean time scales, and spectral shapes of the dielectric relaxation. The faster relaxation modes are attributed to the increasing importance of chain wetting and packing in the interfacial zones around nanofillers, especially in the polymer-grafted system. These insights are used to generate a unifying molecular framework that explains the enhancement in numerous macroscopic physical properties of polymer and polymer-grafted nanocomposites, which suits them for myriad applications.