The additive manufacturing (AM) method of powder bed fusion (PBF) is especially suited for processing semi- crystalline polymers due to the printer's ability to maintain a build volume temperature to control crystallization rate and shrinkage. In PBF, polymers are rapidly heated by the scanning laser and subsequently cooled to the set powder bed temperature, which yields a complex thermal history for printed materials. In this work, fast scanning calorimetry (FSC) is used as a tool to mimic the rapid thermal transitions experienced during PBF of isotactic polypropylene (iPP) powder in order to gain understanding of how the polymer crystallizes during the printing process. FSC is necessary to study the crystallization behavior of iPP during PBF due to the rapid heating and cooling rates of this process. Utilizing in-situ IR thermography in the PBF system, the heating and cooling rates observed for a single-layer PBF print were used to establish the experimental FSC conditions as a mimic for the PBF process. The isothermal crystallization kinetics and non-isothermal crystallization behavior were also investigated by FSC. The crystallization kinetics of iPP exhibits bimodal parabolic-like behavior with the most rapid crystallization occurring at 30 C-degrees. The non-isothermal crystallization behavior exhibits a transition from the alpha-form polymorph crystallization to mesomorphic crystallization at cooling rates > 40 K/s. It is found that partial melting in the printing process leads to self-seeding and increased crystallization onset temperatures upon cooling. The importance of nucleation from surrounding powder and partially melted crystals on the crystallization kinetics and crystal morphology upon melting during the PBF process is shown via this FSC technique. While iPP serves as a material for this analysis, we have uncovered the ability to capture complex morphology evolution during the PBF process to help enable targeted part design and performance for crystallizable polymers. This is a broadly applicable approach to understand how to mimic PBF of any semi-crystalline polymer using FSC.

Poly(ether ether ketone) (PEEK) was found to form gels in the benign solvent 1,3-diphenylacetone (DPA). Gelation of PEEK in DPA was found to form an interconnected, strut-like morphology composed of polymer axialites. To our knowledge, this is the first report of a strut-like morphology for PEEK aerogels. PEEK/DPA gels were prepared by first dissolving PEEK in DPA at 320 °C. Upon cooling to 50 °C, PEEK crystallizes and forms a gel in DPA. The PEEK/DPA phase diagram indicated that phase separation occurs by solid–liquid phase separation, implying that DPA is a good solvent for PEEK. The Flory–Huggins interaction parameter, calculated as χ12 = 0.093 for the PEEK/DPA system, confirmed that DPA is a good solvent for PEEK. PEEK aerogels were prepared by solvent exchanging DPA to water then freeze-drying. PEEK aerogels were found to have densities between 0.09 and 0.25 g/cm3, porosities between 80 and 93%, and surface areas between 200 and 225 m2/g, depending on the initial gel concentration. Using nitrogen adsorption analyses, PEEK aerogels were found to be mesoporous adsorbents, with mesopore sizes of about 8 nm, which formed between stacks of platelike crystalline lamellae. Scanning electron microscopy and X-ray scattering were utilized to elucidate the hierarchical structure of the PEEK aerogels. Morphological analysis found that the PEEK/DPA gels were composed of a highly nucleated network of PEEK axialites (i.e., aggregates of stacked crystalline lamellae). The highly connected axialite network imparted robust mechanical properties on PEEK aerogels, which were found to densify less upon freeze-drying than globular PEEK aerogel counterparts gelled from dichloroacetic acid (DCA) or 4-chlorphenol (4CP). PEEK aerogels formed from DPA were also found to have a modulus–density scaling that was far more efficient in supporting loads than the poorly connected aerogels formed from PEEK/DCA or PEEK/4CP solutions. The strut-like morphology in these new PEEK aerogels also significantly improved the modulus to a degree that is comparable to high-performance crosslinked aerogels based on polyimide and polyurea of comparable densities.

This manuscript describes the synthesis and characterization of guanine and cytosine‐containing supramolecular copolymers, which are inspired from the guanine and cytosine nucleobase pair in deoxyribonucleic acid. Regioselective Michael‐addition allowed the efficient installation of the nucleobases on acrylate‐containing monomers, which enabled the preparation of a series of nucleobase‐functionalized acrylate and n ‐butyl acrylate copolymers using conventional free radical copolymerization. Guanine‐containing copolymers exhibited superior thermal properties, thermomechanical performance, and more defined morphological structure than cytosine‐containing copolymer analogs due to the relatively strong guanine self‐association, thus expanding the potential applications for mechanically reinforced polymeric networks. Blending guanine‐ and cytosine‐containing copolymers formed a supramolecular structure through multiple hydrogen bonding between guanine and cytosine units. The supramolecular blend exhibited intermediate thermomechanical and morphological properties, which suggested that guanine and cytosine units were not fully associated in the random copolymer composition. This work provides valuable fundamental understanding of structure–property‐morphology relationships in acrylic copolymers with the presence of guanine‐cytosine self‐ and complementary interactions, suggesting new understanding in supramolecular design for enhanced mechanical and morphological properties.

Reinforcement of styrene-butadiene rubber/butadiene rubber is achieved by grafting mercapto-functionalized sodium phosphate esters to the rubber during peroxide curing. The size of the anionic phosphate ester moiety is varied by changing the alkyl substituent (ethyl vs octyl) with the intention of modulating the association strength between the grafted ionic dipoles. The concentration of the ionic graft is also varied. These lead to different degrees of reinforcement and dynamic mechanical properties of the vulcanized rubber. The morphologies of ionic aggregates are characterized by transmission electron microscopy (TEM) imaging and X-ray scattering experiments. TEM imaging revealed heterogeneities in the material, which sometimes included the formation of vesicular aggregates with diameters of approximately 20-30 nm. These features are consistent with the radius of gyration calculated from a knee observed in X-ray scattering at scattering vectors below 0.4 nm(-1). Smaller aggregates were analyzed using the Kinning-Thomas liquid-like hard sphere model and were found to be similar in radius (similar to 1.2-1.3 nm), irrespective of the molar volume of the ionic grafts from which they were constituted. However, the number of aggregates per unit volume within the material and the aggregation number are both profoundly affected by such variations. The structural variations of the ionic graft give rise to substantial changes in the tensile properties of the rubber at room temperature. At high temperatures, the differences in the dynamic moduli substantially diminish among the ionically grafted vulcanizates but remain substantial between the vulcanizates with and without ionic grafts. The equilibrium moduli of all vulcanizates converge at 60 degrees C. Possible mechanisms responsible for reinforcement are discussed at various temperatures, time scales, and ionic graft concentrations.

A round-robin study has been carried out to estimate the impact of the human element in small-angle scattering data analysis. Four corrected datasets were provided to participants ready for analysis. All datasets were measured on samples containing spherical scatterers, with two datasets in dilute dispersions and two from powders. Most of the 46 participants correctly identified the number of populations in the dilute dispersions, with half of the population mean entries within 1.5% and half of the population width entries within 40%. Due to the added complexity of the structure factor, far fewer people submitted answers on the powder datasets. For those that did, half of the entries for the means and widths were within 44 and 86%, respectively. This round-robin experiment highlights several causes for the discrepancies, for which solutions are proposed.

Utilizing a thermally induced phase separation process, poly(phenylene sulfide) (PPS) thermoreversible gels are developed using for the first time a benign solvent, 1,3-diphenylacetone (DPA). The PPS/DPA phase diagram revealed a solid- liquid phase separation mechanism often observed with crystallizable polymers in good solvents. Two different methods of determining the Flory-Huggins interaction parameter, ?, were utilized to understand the polymer-solvent interactions that govern the phase behavior. Using an experimental approach, a melting point depression curve was fit to experimental PPS/DPA melting point data, revealing an interaction parameter of ? = 0.41. Using accepted Hansen solubility parameters of PPS and calculated parameters for DPA via a group contribution method, the polymer-solvent interaction parameter was estimated to be? = 0.49. The reasonable agreement between both methods indicates good interactions between PPS and DPA and verifies the calculated solubility parameters for DPA. Upon gelation at temperatures below 225 degrees C, subsequent solvent evacuation via freeze-drying yields aerogels with low densities ranging from 0.11 to 0.25 g/cm(3) and volumetric porosities ranging from 92.3 to 82.2%. The physical properties of the PPS aerogels were found to be comparable to similar aerogels made from poly(ether ether ketone) (PEEK). Ultra-small to wideangle X-ray scattering (USAXS/SAXS/WAXS) profiles reveal an ordered, hierarchical morphology with sharp interfaces, whereby the microstructure is composed of semicrystalline aggregates of stacked lamella. Scanning electron microscopy micrographs indicate that the PPS aerogels are highly porous and that the lamellar stacks take the form of elongated, interconnected fibrils. Power-law scaling of aerogel density with compressive modulus suggests a tendency of the interconnected lamellar aggregates to bend and/or buckle in compression in a manner similar to strut deformation in open-celled foams. Despite their similar physical properties, PPS aerogels demonstrated higher moduli than PEEK aerogels at comparable densities due to their network-like morphology.

Degradable poly(ethylene glycol) (PEG) hydrogels provide a versatile platform for drug delivery and tissue engineering, and acetal functionalization now enables photoprocessible PEG oligomers with selective and facile degradation in acidic environments. Tailored morphologies within acetal-functionalized hydrogels provided fundamental understanding of the multiphase network degradation. End group modification of poly(ethylene glycol) (Mn = 2,000 g/mol) with 2-(vinyloxy)ethyl acrylate yielded polyether precursors with both pH-sensitive acetals and photo-curable acrylate end groups. UV-initiated binary thiolacrylate crosslinking of the acetal-functionalized PEG diacrylate with varied amounts of a thiolfunctionalized three-armed PEG provided pH-degradable networks. Controlled stoichiometric imbalance of thiol and acrylate functionalities ensured predictable plateau storage moduli from 2 x 105 to 8 x 105 Pa. Small-angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA) confirmed that the thiol/acrylate molar ratio provided hydrogels with varying network architectures and crosslink densities. Spectroscopic monitoring of an imbedded mobile dye (Direct Red-81) quantified hydrogel degradation rates. Degradable hydrogels exhibited bulk degradation in acidic solution. Gels with the lowest crosslink density fully degraded in aqueous solutions at pH 3.4 within 60 h, while the highly crosslinked gels fully degraded over 3 weeks. All hydrogels displayed long-term stability in phosphate-buffered saline (pH 7.4) beyond 3 mo, suggesting stable hydrogels for selective degradation and cargo release in low pH environments.

Growing demands in flexible electronics have stimulated the rapid development of electrodes with multifaceted attributes. Porous carbon fibers (PCFs) provide a potential means to simultaneously achieve flexibility, durability, and energy density. High energy density often necessitates large surface areas and thus pores, but pores generally diminish the mechanical PAN) and examine the changes in the polymer morphology and resulting PCF porosity and flexibility in response to relative humidity (R.H.). The determining factors of the fiber morphology evolve from block copolymer microphase separation at 40-50% R.H. to vapor-induced phase separation (VIPS) combined with microphase separation at 60-70% R.H. and to vapor-induced precipitation at 80-90% R.H. After pyrolysis, the PCFs show the corresponding porosity, flexibility, and electrochemical properties. Because VIPS enables the polymer fibers to outwardly reorganize PAN and produce continuous graphitic structures, PCFs prepared from polymer fibers electrospun at 70% R.H. develop a mesoporous core and long-range graphitic carbon sheath. Owing to the core-sheath structure, these PCFs exhibit mechanical strength to withstand repeated bending while retaining a 249 +/- 20 F g-1 capacitance in flexible capacitor assemblies. This work highlights the potential for controlling block copolymer morphologies by processing conditions and PCF properties, providing a platform for designing flexible PCFs for energy and environmental sciences.

Lignin is one of the most abundant biopolymers in nature. Although lignin-derived hard carbon (L-HC) has potential to be used as a sodium-ion battery (SIB) anode but is limited by its poor electrochemical performance. In nature, lignin normally coexists with cellulose and hemicellulose in agricultural biomass, and studies have applied different agricultural biomasses to make SIB anodes; however, the underlying mechanism, especially the functionality of each component, is still unclear. In this study, we aim to combine lignin with cellulose and/or hemicellulose to produce hard carbons with outstanding electrochemical performance and low cost, and more importantly, unveil the underlying mechanisms. We found that the poor electrochemical performance of L-HC was mainly due to its large surface area with high amount of oxygen-containing functional groups and its unique physical structure that inhibit effective Na diffusion. Combining lignin with either cellulose or hemicellulose led to significantly improved electrochemical performance of the resulting hard carbon, with cellulose mainly contributing to the increase of capacity and hemicellulose mainly contributing to the stability of capacity during cycling and at high current density. Based on the comprehensive consideration of both electrochemical performance (half and full cells) and economic perspectives, lignin combined with cellulose showed great potential. Our study shed light on the contributions of each major biomass component on physical and electrochemical properties of resulting hard carbon and designed a unique way to improve L-HC.

Crystallization inhibitors in amorphous solid dispersions (ASD) enable metastable supersaturated drug solutions that persist for a physiologically relevant time. Olefin cross-metathesis (CM) has successfully provided multifunctional cellulose-based derivatives as candidate ASD matrix polymers. In proof of concept studies, we prepared hydrophobic bile salt/cellulose adducts by CM with naturally occurring bile salts. We hypothesized that increased hydrophilicity would enhance the ability of these conjugates to maximize bioactive supersaturation. Their selective preparation presents a significant synthetic challenge, given polysaccharide reactivity and polysaccharide and bile salt complexity. We prepared such derivatives using a more hydrophilic hydroxypropyl cellulose (HPC) backbone, employing a pent-4-enyl tether (Pen) for appending bile acids. We probed structure-property relationships by varying the nature and degree of substitution of the bile acid substituent (lithocholic or deoxycholic acid). These conjugates are indeed synergistic inhibitors, as demonstrated with the fast-crystallizing prostate cancer drug, enzalutamide. The lithocholic acid methyl ester derivative, AcrMLC-PenHHPCPen (0.64), increased induction time 68 fold vs. drug alone.

This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Reversible addition-fragmentation chain transfer polymerization afforded a library of A-AB-A acrylic triblock copolymers, wherein the A unit contained cytosine acrylate (CyA) or post-functionalized ureido cytosine acrylate (UCyA) and the B unit consisted of n-butyl acrylate (nBA). Differential scanning calorimetry revealed two glass transition temperatures, suggesting microphase-separation in the A-AB-A triblock copolymers. Thermomechanical and morphological analysis revealed the effects of hydrogen bonding distribution and strength on the self-assembly and microphase-separated morphology. Dynamic mechanical analysis showed multiple tan delta (δ) transitions that correlated to chain relaxation and hydrogen bonding dissociation, further confirming the microphase-separated structure. In addition, UCyA triblock copolymers possessed an extended modulus plateau versus temperature compared to the CyA analogs due to the stronger association of quadruple hydrogen bonding. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. In contrast, UCyA triblock copolymers lacked long-range ordering due to hydrogen bonding induced phase mixing. The incorporation of UCyA into the soft central block resulted in improved tensile strength, extensibility, and toughness compared to the AB random copolymer and A-B-A triblock copolymer comparisons. This study provides insight into the structure-property relationships of A-AB-A supramolecular triblock copolymers that result from tunable association strengths.

The aspect ratio (AR) of filler particles is one of the most critical determinants for the mechanical properties of particle-reinforced polymer composites. However, it has been challenging to solely study the effect of particle AR due to the difficulties of controlling AR without altering the physical and chemical properties of the particle. Herein, we synthesized PCN-222, a zirconium-based porphyrinic metal-organic framework (MOF) with preferential longitudinal growth as a series of particles with ARs increasing from 3.4 to 54. The synthetic MOF conditions allowed for the chemical properties of the particles to remain constant over the series. The particles were employed as reinforcers for poly(methyl methacrylate) (PMMA). MOF-polymer composite films were fabricated using doctor-blading techniques, which facilitated particle dispersion and alignment in the PMMA matrix, as revealed by optical microscopy and wide-angle X-ray diffraction. Mechanical measurements showed that both elastic and dynamic moduli increased with particle AR and particle concentrations but started to decrease as particle loading increased beyond 0.5 wt % (1.12 vol %). The data obtained at low particle loadings were fitted well with the Halpin-Tsai model. In contrast, the percolation model and the Cox model were unable to adequately fit the data, indicating the mechanical reinforcement in our system mainly originated from efficient load transfer between particles and the matrix in the particle orienting direction. Finally, we showed that the thermal stability of composite films increased with the addition of MOF particles because of the high thermal degradation temperature and restricted polymer chain mobility.

This manuscript describes a synthetic strategy and structure–property investigation of unprecedented phosphonium-based zwitterionic homopolymers (polyzwitterions) and random copolymers (zwitteriono...

Preparation of polysaccharide-based block copolymers with linear architectures is an important goal, opening up clear application potential and requiring significant advances in polysaccharide regio- and chemoselectivity. Herein we report a simple approach to prepare dextran-based block copolymers. Reaction with N-bromosuccinimide (NBS)/triphenyl phosphine (PPh3) regioselectively brominates the sole primary alcohol of linear, unbranched dextran at C-6 of the nonreducing end monosaccharide. The resulting dextran, monofunctionalized with a terminal C-6 bromide, was coupled with various amine terminated polymers to prepare block copolymers, including dextran-b-poly(ethylene glycol), dextran-b-polystyrene, and dextran-b-poly(N-isopropylacrylamide). These renewable-based block copolymers, prepared in two selective, high-yielding steps from native linear dextran, exhibit various interesting properties. Dextran-b-poly(N-isopropylacrylamide) undergoes thermally induced micellization as revealed by dynamic light scattering (DLS), forming micelles upon exceeding 33 °C. We also observed microphase separation in dextran-b-polystyrene by using small-angle X-ray scattering (SAXS). Overall, this methodology provides a new, highly chemo- and regioselective, versatile route to diverse dextran-based block copolymers with useful properties, enabling drug delivery, compatibilization, and other applications.

This manuscript describes the versatility of highly-directional, noncovalent interactions, i.e., quadruple hydrogen bonding (QHB), to afford novel polyurea segmented supramolecular polymers for melt extrusion 3D printing processes. The molecular design of the polyurea elastomers features (1) flexible polyether segments and relatively weak urea hydrogen bonding sites in the soft segments to provide elasticity and toughness, and (2) strong ureido-cytosine (UCyt) QHB in the hard segment to impart enhanced mechanical integrity. The resulting polyureas were readily compression-molded into mechanically-robust, transparent, and creasable films. Optimization of polyurea composition offered a rare combination of high tensile strength (95 MPa), tensile elongation (788 % strain), and toughness (94 MJ m-3), which are superior to a commercially available Ninjaflex® elastomer. The incorporation of QHB facilitated melt processability, where hydrogen bonding dissociation provided low viscosities at printing temperatures. During cooling, directional self-assembly of UCyt QHB facilitated the solidification process and contributed to part fidelity with the formation of a robust physical network. The printed objects displayed high layer fidelity, smooth surfaces, minimal warpage, and complex geometries. The presence of highly-directional QHB effectively diminished mechanical anisotropy, and the printed samples exhibited comparable Young's moduli along (x-y direction, 0 o) and perpendicular to (z-direction, 90 o) the layer direction. Remarkably, the printed samples exhibited ultimate tensile strains approaching 500 % in the z-direction prior to failure, which was indicative of improved interlayer adhesion. Thus, this design paradigm, which is demonstrated for novel polyurea copolymers, suggests the potential of supramolecular polymers with enhanced mechanical performance, melt-processability, recyclability, and improved interlayer adhesion for melt extrusion additive manufacturing processes.

This work unravels the bulk microstructure of a doubly charged homopolymer by correlating crystallographic details from single-crystal X-ray diffraction (SCXRD) of the monomer with the crystalline order of the polymer utilizing powder X-ray diffraction (PXRD). The homopolymer, synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization, features a styrenic backbone with amphiphilic pendant groups containing a doubly charged 1,4- diazabicyclo[2.2.2]octane (DABCO) salt that is attached to a terminal octadecyl (C-18) chain. SCXRD of the single crystals grown from the monomers reveals that the amphiphilic monomers prefer to pack into a highly ordered herringbone lamellar structure that facilitates electrostatic interactions between the DABCO salt units and hydrophobic associations of the styrene moieties and pendant C-18 chains. Following living radical polymerization from a homogeneous solution, the resulting homopolymer was found to be semicrystalline, despite the expected stereoirregularity (atactic configuration) of the styrenic backbone. Surprisingly, comparisons of the PXRD patterns of the monomer and annealed homopolymer suggest that the homopolymer also crystallizes into a herringbone lamellar structure similar to that of the monomer. Moreover, the V-shaped counterion geometry likely plays an important role in the formation of the herringbone structure for the monomer and the homopolymer to maximize dipole-dipole interactions. Through correlations of the precise crystallographic details of the monomer with the PXRD patterns of the semicrystalline homopolymer, this study highlights a powerful approach in developing a structural model to define the morphology of polymers with complex chemical structures and hierarchical ordering.

This manuscript describes the structure-property-morphology relationships of doubly charged 1,4-diazabicyclo[2.2.2]octane (DABCO) salt-containing ABA triblock ionomers. The triblock copolymers consist a soft poly(n-butyl acrylate) (PnBA) central block and two external styrenic hard blocks bearing amphiphilic pendant C-18-alkyl groups and doubly charged salt units. Surprisingly, the DABCO salt-containing ABA block copolymers preserved the thermomechanical integrity until degradation, which indicated the formation of a reinforcing physical network compared to the corresponding doubly charged random copolymers and singly charged block copolymer analogs. Small-angle X-ray scattering data revealed that the DABCO-based ABA block copolymers self-assembled into highly ordered hierarchical microstructures, in which the soft and hard domain of the block copolymers phase-separated into highly ordered lamellar morphologies. Moreover, a secondary structure that originated from the ordering of the amphiphilic pendant groups formed within the lamellar hard domain. The interesting thermal, thermomechanical, and morphological properties of doubly charged ionic block copolymers open promising avenues for the synthesis of novel thermoplastic elastomers.

Fully-aromatic homopolyester based on biphenyl 3,4′-bibenzoate facilitated a nematic mesophase and restricted crystallization.