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This study focuses on functionalizing polycyclooctene (PCOE) with thioacetate groups using thiol–ene click chemistry. The ethylene thioacetate (EVSA) copolymers produced vary in thioacetate incorporation (4–25 mol %) via a controlled semibatch addition technique with AIBN dosing. Copolymers with 4–14 mol % thioacetate are semicrystalline, while those with 20–25 mol % are amorphous. Increased functionalization correlates with decreased crystallinity and increased stretchability, with the highest functionalization (25 mol %) showing a modulus of 0.045 MPa and 2000% elongation at break. This behavior is due to the pseudoprecise functionalization of the thioacetate pendants and intrinsic cross-linking that occurs during melt processing. Broadband dielectric spectroscopy (BDS) indicates a low activation energy barrier (16 kJ/mol for the β process), suggesting potential self-healing applications.

Polymer–nanoparticle interactions play an important role in determining the morphology and properties of polymer nanocomposites and controlling the polymeric reactions involving heterogeneous catalysts. Here, we modulate the interactions between nonpolar polymers and nanoparticles by modifying the nanoparticle surface chemistry and quantify the interaction strength through direct contact angle measurements. We investigate the interactions of three nonpolar polymers, polystyrene, polyethylene, and polycyclooctene, with silica nanoparticles whose surface chemistry has been modified by atomic layer deposition of titania and calcium carbonate and by alkyl silanization. Significant differences in polymer–nanoparticle interactions are observed, which can be attributed to differences in the polarizability of the polymers and oxide surface composition. Compared to fully hydrogenated polycyclooctene, polycyclooctene is shown to have stronger interactions with most metal oxides; however, this trend is reversed following alkyl silanization of the silica nanoparticles, which makes the surface of the particles less polar. These differences in interactions can be leveraged to make polymer nanocomposites with unique properties and enable the selective conversion of polymers without the need for separations.

Associating polymers have recently attracted tremendous attention as self-healing polymers due to the dynamic reversibility of sticker association–dissociation processes. These sticker dynamics inevitably slow significantly as segmental dynamics decelerate below the glass transition temperature that limits the operational temperatures of associating polymers. Using broadband dielectric spectroscopy on a new set of associating polymers composed side chains of various lengths and terminal carboxylic-acid sticker functionality, we discovered an unexpected decoupling near the glass transition (Tg) between the slower backbone and fast sticker motions. These two motions have distinct activation energies for the motion of the sulfur linkage adjacent to the backbone (∼22 to 26 kJ/mol) and the carboxylic acid groups (∼5 to 8 kJ/mol). A second decoupling appears in the polymer with the longest side chain length at Tg– 20 K, reflecting the dynamics of various carboxylic acid binding configurations. Our findings open the door to design associating polymers with the capability of sticker association/dissociation at low temperatures.

Cyclic ketene acetals (CKAs) possess unique features in two aspects. On one hand, after the addition of a radical on the alkene, CKAs can undergo ring‐opening via radical rearrangement, enabling polyester preparation based on chain‐growth polymerization. On the other hand, the alkene connected with two electron‐donating oxygens in a strained form exhibit unique reactivities, resulting in complex reactions in the presence of electron deficient compounds. In this investigation, fundamental studies on CKA radical ring‐opening polymerization and charge‐mediated reactions were performed. Alternating copolymers of CKA and maleimides, or maleates, were prepared and characterized. Quantum chemistry modeling from the perspectives of reaction kinetics and thermodynamics enabled an in‐depth mechanistic study on the side reactions between CKA and maleic anhydride or itaconic anhydride, inspiring the techniques to minimize those side reactions in competition with radical copolymerization. After purifying the anhydride monomers with sublimation, the copolymerization with CKA successfully occurred. The anhydride containing polyester structures with an alternating sequence were confirmed with comprehensive characterizations. Facile post‐functionalization with an alcohol was performed, resulting in carboxylate containing polyesters.

Upcycling of waste polyolefins into higher-value functional polymers through chemical functionalization is a promising strategy to recover value and minimize their environmental impact. We report the hydrocarboxylation of polycyclooctene as a model for accessing ethylene acrylic acid copolymers (EAA) from waste polyethylene. The effects of various process parameters on the hydrocarboxylation were investigated. The relationship between carboxylic acid concentration and material properties, including crystallinity, melting temperature, glass transition temperature, adhesive properties, and wettability, was studied in comparison to an unfunctionalized polyethylene. Among the catalysts evaluated, Co2(CO)8exhibited relatively slow kinetics toward the hydrocarboxylation and was not compatible with 2,6-di-tert-butyl hydroxytoluene, a common additive present in commercial polyolefins. PdCl2(PPh3)2exhibited a higher reactivity toward the hydrocarboxylation, though polymer gelation was observed with extended reaction times or high catalyst loadings. Carboxylic acid incorporation into the polymer was readily controlled by varying the reaction time. Overall, the resultant COOH-functionalized polyolefins possessed properties analogous to commercial EAA.

Performance of polymer electrolyte-based energy systems is significantly impacted by transport within the electrode catalyst layer, where ionomer thin films coat catalyst particles. Proton exchange ionomer thin films have been thoroughly characterized, but few studies have critically examined anion-exchange ionomer (AEI) thin films. Further, none have reported nanoscale phase separation for hydrocarbon AEIs, which is critical to mitigate transport resistances. In this work, a set of hydrocarbon-based AEIs with nanoscale phase separation are developed from tunable block copolymer systems composed of polyisoprene (PIp) and polychloromethylstyrene (PCMS). The effect of the PIp/PCMS ratio, architecture, and thickness on the thin-film morphology of the neutral block copolymer precursors on silicon and silver substrates is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM). AEIs are prepared by quaternizing with trimethylamine or methylpiperidine and their cation-dependent morphology is characterized at 60 °C and 95% RH. A perpendicularly aligned morphology is observed on silver, while no phase separation is observed on silicon, indicating that silver–polymer interfacial interactions drive phase separation. After quaternization, dipole–dipole interactions induce some disorder, but nanoscale phase separation is still maintained. GISAXS patterns are modeled using a Unified Fit approach to understand water uptake and swelling, and recommendations for AEI design are presented.

The electrospinning field is dominated by studies that investigate parameters, such as polymer concentration and chain length, to identify conditions where the polymer chains are sufficiently entangled to facilitate fiber formation. Here, we report the first demonstration that linear, nonentangled, oligomeric polyelectrolytes can be electrospun into fibers using a traditional single-nozzle setup. Previously, we have demonstrated that the associative phase separation phenomenon known as complex coacervation facilitates the electrospinning of polyelectrolyte complex fibers directly from water. In this work, we synthesized polycations and polyanions with degrees of polymerization ranging from ∼500 down to <10, representing average molecular weights on the order of 100 to 1 kg/mol. We then quantified the phase behavior and viscosity of our various coacervate samples as a function of both chain length and salt concentration. Our results confirm that the polymer concentration in all samples was near or above the estimated value for the overlap concentration and that only the longest polymer samples were expected to experience entanglements. However, we were able to electrospin fibers from all of our coacervate samples, even oligomers. Thus, the electrospinnability of coacervates is fundamentally different from the traditional electrospinning of linear, neutral polymers or solutions composed of polyelectrolytes mixed with neutral polymers. In the same way that coacervation represents a novel way to enable the electrospinning of polyelectrolytes from water, the associative interactions driving phase separation eliminate the need for entanglements by slowing the timescale for relaxation. Our results suggest an alternative route that enables the electrospinning of novel solutions by decoupling chain-length requirements from other length-dependent parameters.

Random copolymers of poly(4‐vinylpyridine) and polyisoprene were synthesized, and subsequently quaternized with 1‐alkylbromides. The number of carbons on the pendant side‐chain of the resultant comb‐shaped polymer, n, ranged from 2–8.The comb‐shaped polymers were crosslinked employing thiol‐ene chemistry to give mechanically robust ion conducting membranes. Analysis by wide and medium‐angle X‐ray scattering show three morphology regimes that are dependent on the number of carbons on the pendant side‐chains. When n =2, ionomer cluster morphology was dominant, when n =8 backbone‐backbone morphology was dominant, and when n =3–6, the membrane showed a coexistence of both ionomer cluster and backbone‐backbone morphologies. Evaluation of the water uptake of the membranes showed a maximum water uptake per cation of 9.5 when n =5 at 95% relative humidity (RH) and 60°C. Conductivity of the samples characterized by electrochemical impedance spectroscopy showed bromide conductivity as high as 110 mS/cm when n =3 at 95% RH and 90°C. Parabolic dependence of ionic conductivity on the number of carbons on the pendant side‐chains in crosslinked, random, comb‐shaped, poly(4vinylpyridine)‐ran‐polyisoprene membranes. Maximum ionic conductivity was observed for membranes with 3 carbons on the pendant side‐chain, which exhibited a coexistence morphology.

The role of counterion sterics on the structure and dynamics of a low glass transition temperature, amorphous poly(isoprene-ran-styrenesulfonate) copolymer was investigated using a series of symmetric, tetraalkylammonium counterions with methyl (TMA), ethyl (TEA), propyl (TPA), and butyl (TBA) pendent groups, in addition to a sodium (Na) control. A detailed analysis of the aggregate structure was achieved by fitting the copolymers’ X-ray scattering profiles with a modified hard sphere model. Increasing the counterion sterics from Na to TEA resulted in slight changes to the aggregates with some ionic groups present in the isoprene matrix. For the more hindered TPA and TBA counterions, considerable disruption of the structure occurred. Using solid-state NMR, dynamic mechanical analysis, and rheology, the effect of the counterion sterics on the copolymer’s dynamics was determined. The T1ρrelaxation of the copolymers revealed a rigid isoprene fraction, associated with the ion clusters, and a mobile isoprene matrix fraction. Copolymers with larger counterions exhibited an increase in the dynamic moduli at high frequency and a decrease in the dynamic moduli at lower frequencies in addition to possessing faster molecular dynamics. These two observations are attributed to an increased incorporation of ionic groups into the isoprene matrix and screening of the dipole–dipole interactions.

Polymeric membranes are ubiquitous in transport applications including gas separation, water desalination, solid-state batteries, and fuel cells. The transport mechanism in certain classes of membranes is well understood. It is generally believed that polymeric membranes used in gas separation follow the solution–diffusion model. However, the transport mechanism in other membranes such as the ones used in water desalination is less clear as both the solution–diffusion and hydrodynamic models have been proposed. In this contribution, we study the structure as well as the water and polymer dynamics of several polymeric membranes using small-angle and quasi-elastic neutron scattering. We demonstrate that on the scale of a few nanometers, water appears to diffuse through a desalination membrane at a rate comparable to bulk water, while water diffuses at a rate that is a factor of 2 slower in an anion-exchange membrane. These results illustrate the importance of studying both the structure and dynamics of membrane materials and have important implications in understanding the transport mechanisms that differentiate the different types of polymeric membranes.

The performance of ion-exchange membranes in fuel cells is critically linked to their ion-conducting morphology. In this report, we analyzed the connectivity of anion-exchange membranes (AEMs) by electrostatic force microscopy (EFM). As a tapping-mode AFM-based technique, EFM probes height, phase, and electrostatic force gradient through two-pass interleave scans, which reveals the direct relationship between membrane surface morphology and connectivity of the ionic domain. The AEMs are diblock copolymers of a polyisoprene (PIp) block and a polystyrenic block containing the phosphonium ion (P(R3P+)MS). Different alignments of cylinders were observed in the bulk and on the surface for AEMs with different ion-exchange capacities (IECs) and preparation methods. The impacts of the cylinder alignment on the connectivity of the ionic domain were then investigated by EFM. For AEM 13 with IEC = 0.44 mmol/g and a hexagonal morphology, cylinders aligned parallel to the surface, which led to many disconnected regions observed throughout the membrane. In contrast, the perpendicularly aligned channels of AEM 16 with IEC = 0.87 mmol/g consisted only of a well-connected ionic phase throughout the membrane.

Diblock copolymers of isoprene and chloromethylstyrene were synthesized by nitroxide-mediate polymerization. The polychloromethylstyrene block was quaternized with tris(trimethoxyphenyl)phosphine (P(Ph(OMe)3)3) or triphenylphosphine (P(Ph)3). Membranes with ion-exchange capacity (IEC) ranging from 0.87 to 2.35 mmol/g were prepared. The bulk morphology was investigated via small-angle X-ray scattering and transmission electron microscopy, where hexagonal and body-centered cubic morphologies were observed. The surface morphology was revealed by atomic force microscopy where both parallel and perpendicular alignments were observed. Compared to P(Ph(OMe)3)3, P(Ph)3exhibits higher quaternization efficiency due to less steric hindrance. Partially quaternized membranes were prepared using P(Ph)3, and the dependence of domain size on the quaternization level is discussed. The morphologies as a function of relative humidity were investigated. For high IEC membranes, although bulk scattering showed small changes in d-spacing, large changes in domain size on the surface occurred between hydrated and dehydrated conditions. Further investigations of morphological reversibility by humidity cycling showed good recovery between humid and dry conditions, indicating that the expansion and contraction of channels is a reversible process.

For polymer nanocomposites with two-dimensional filler materials, intercalation/exfoliation is required to maximize internal connectivity. Previous work has shown that clay exfoliation can be achieved through mild thermal annealing in the presence of a low-molecular-weight, hydroxyl-terminated “telechelic” polybutadiene (tPB) matrix. However, the specific role of the hydroxyl groups, their placement, and polymer mobility in the intercalation/exfoliation process still remains unclear. In this study, these matrix parameters were evaluated by replacing the tPB with randomly functionalized polybutadienes (rPBs) of increasing hydroxyl group densities. The rPB was synthesized by covalently grafting mercaptoethanol to the PB backbone, and its ability to exfoliate organically modified montmorillonite clay was evaluated. While some functional groups are required to exfoliate the clay, it was found that exfoliation proceeds successfully regardless of the number of hydroxyl groups or their location on the PB backbone. Instead, it was found that polymer mobility played a key role in the extent of exfoliation. As the grafting concentration was increased, the rPB molecular mobility decreased because of its higher glass transition temperature (Tg). A detailed analysis of their linear viscoelastic properties was able to decouple the two phenomena, change in mobility and effectiveness of polymer–clay interaction. Nanocomposites using highly grafted polymers showed a decrease in their connectivity because of reduced exfoliation of the clay. This was overcome by introducing a highly grafted and highly mobile rPB with a low Tg(low vinyl content), which successfully exfoliated the clay. The combined results suggest that intercalation can be achieved through favorable polymer–clay interactions, whereas exfoliation can proceed beyond intercalation only when there is enough polymer mobility.

We report the design, synthesis, and characterization of a series of thieno[3,4-b]thiophene acceptor blocks with octyl (T8), phenyl (TP), perfluorooctyl (TF8), and perfluorophenyl (TFP) side groups. Their subsequent copolymerization with dithienylbenzodithiophene by direct arylation polymerization afforded novel low bandgap poly(thienothiophene-alt-dithienylbenzodithiophene) (PTB) polymers. The strongly electron withdrawing TF8 and TFP groups were shown to significantly lower both EHOMOand ELUMOlevels and gave computed copolymer ground-to-excited state dipole changes (Δμge) that were relatively higher than for the nonfluorinated analogues. These materials show favorably aligned energy levels relative to conventional fullerene-type acceptors, which should allow them to perform well in organic photovoltaics.

Poly(isoprene-ran-dimethyloctylammonium styrenesulfonate) (P(I-ran-DMOASS)) copolymers with high molecular weights and dimethyloctylammonium styrenesulfonate (DMOASS) compositions ranging between 8 and 40 mol % (30 and 77 wt %) were synthesized via nitroxide-mediated polymerization. Thermal and viscoelastic characterization revealed distinct behaviors for the low (30–51 wt %) and high (56–77 wt %) DMOASS content copolymers. Three structural regimes were identified: ion clusters (30 wt % DMOASS), continuous ionic phase (56–77 wt % DMOASS), and the coexistence of the two (42–51 wt % DMOASS). As DMOASS content increased, small-angle X-ray scattering revealed a gradual transition from the characteristic ion cluster structure to a smaller, more regular backbone–backbone structure associated with a continuous ionic phase. The ion clusters acted as physical cross-links and introduced additional elasticity into the low DMOASS content copolymer, while the continuous ionic phase showed restricted flow behavior and the disappearance of a definitive plateau modulus. Dynamic mechanical analysis revealed two distinct Tg’s at intermediate DMOASS content, indicating the coexistence of both structures.

Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when two different metallic species are mixed at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods was then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence dependence in both surface structure and surface composition. Replica exchange with solute tempering molecular dynamics simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces viadifferent mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged for rational bimetallic nanoparticle design using peptide-enabled approaches.

Star block copolymers (s-BCPs), comprised of multiple linear diblock copolymers joined at a central point, are shown to segregate to the interface between two immiscible homopolymers that are identical to the blocks of the s-BCPs. The s-BCPs undergo a configurational transition at the interface, with different blocks of copolymers being embedded in their respective homopolymers, thereby bridging the interface and promoting adhesion. A series of 4-arm s-BCPs were synthesized with hydrogenated or deuterated polystyrene (PS/dPS) as the core block and poly(2-vinylpyridine) (P2VP) as the corona block, which was directly placed at the interface between the two homopolymers. Neutron reflectivity (NR) was used to determine the concentration profiles of the PS homopolymer, s-BCP core blocks, and P2VP total segments under equilibrium. The investigation varies the molecular weight (MW) and the total number of s-BCPs at the interface. Self-consistent-field theory (SCFT) was also employed to calculate the concentration profiles of the components at the interface, which were in excellent agreement with experimental results. The NR showed that the interfacial width between the homopolymers increased with the increasing number of s-BCPs at the interface up to a saturation limit. Beyond this limit, additional s-BCPs were released into the corona-miscible phase as unimolecular micelles. For a comparable interlayer thickness of s-BCPs at the interface, lower MW s-BCPs generated a broader interface. SCFT analysis suggested that, at the same packing density, the arms of the low MW s-BCPs align more parallel to the interface, while the arms of high MW s-BCPs adopt a more normal orientation, like their linear BCP counterparts. Furthermore, it was also observed that the core blocks, constrained by the junction points, were oriented more parallel and closer to the interface than the corona blocks. The phase behavior of the polymer blends revealed that s-BCP additives can efficiently reduce the domain size, with the low MW yielding smaller domain sizes due to the greater reduction in the interfacial energy and the high MW arresting phase separation due to their higher binding energy and a jamming of the interfacial assemblies. Asymmetric double cantilever beam (ADCB) tests demonstrated that s-BCPs promoted adhesion more efficiently than their linear BCP counterparts due to stronger binding energy per molecule, suggesting a more efficient compatibilizer for polymer upcycling. The results from these studies provide fundamental insights into the assembly of s-BCPs at homopolymer interfaces, the reduction of domain size, and promotion of adhesion, providing a strategy for the use of s-BCPs as stealth surfactants and universal compatibilizers.

Hybrid conjugated polymers containing carborane directly bonded in the aromatic backbone repeat structure have interesting electronic bonding structures and are potentially useful new materials in organic electronics. Conjugated polymers based on o-carborane are particularly interesting for applications in sensing and detection because of the cage’s unique bonding scheme and its bent geometry. Poly(fluorene) containing o-carborane displays multiple emission pathways that can be modulated through interactions with small molecules. In this paper, we report that films of poly(fluorene) with o-carborane in the backbone function as vapochromatic photoluminescent sensors toward volatile organic molecules.

The synthesis of a novel silylcarborane acrylate monomer is reported as well as its application as an etch-resistant component for the formulation of imprint layers for UV nanoimprint lithography (NIL). By introduction of 10% by weight of the silylcarborane acrylate monomer into NIL resist formulations, the oxygen plasma etch rate of the resulting film was reduced by nearly a factor of 2. When used in NIL, the patterned resist layer had excellent oxygen plasma etch resistance, leading to effective image transfer to the underlying poly(hydroxyethyl methacrylate) lift-off layer. The latter allowed for the fabrication of metallic interdigitated electrode patterns via a NIL/lift-off process. This work demonstrates the robustness of silylcarborane-containing resists and paves the way for the investigation of new, high-resolution patterning methods.

Preparative methods for the incorporation of polyhedral oligomeric silsesquioxane POSS macromonomers into ethylene–propylene EP polymers have been developed that utilize metallocene polymerization. Analysis of these novel ethylene–propylene–POSS polymers using wideangle Xray diffraction reveals that pendant POSS groups off the polymer backbones aggregate with a phenyl periphery, and the polymers crystallize as anisotropically shaped nanocrystals. POSS particle aggregation is strongly dependent on the nature of the POSS peripheral group. XRay studies suggest that aggregation of POSS in the EP elastomers did not occur with isobutyl and ethyl peripheries, as they disperse within the polymer matrix. The formation of POSS nanocrystals increases the mechanical properties of these thermoplastic elastomers. The tensile storage modulus increases significantly with the addition of POSS, as does the length of the rubbery plateau region. Tensile studies reveal an elongation at break of 720 for one EPphenyl POSS polymer sample, with the others between 400 and 500.

In this study, amphiphilic polyoxanorbornene with different quaternary alkyl pyridinium side chains were synthesized. The biological efficiencies of these polymers, with various alkyl substituents, were determined by bacterial growth inhibition assays and hemolytic activity (HC50) against human red blood cells (RBCs) to provide selectivity of these polymers for bacterial over mammalian cells. A series of polymers with different alkyl substituents (ethyl, butyl, hexyl, octyl, decyl and phenylethyl) and two different molecular weights (3 and 10 kDa) were prepared. The impact of alkyl chain length divided the biological activity into two different cases: those with an alkyl substituent containing four or fewer carbons had a minimum inhibitory concentration (MIC) of 200 µg · mL−1 and a HC50 greater than 1 650 µg · mL−1, while those with six or more carbons had lower MICs ≤ 12.5 µg · mL−1 and HC50 ≤ 250 µg · mL−1. Using MSI-78, the potent Magainin derivative which has an MIC = 12.0 µg · mL−1 and HC50 = 120 µg · mL−1, as a comparison, the polymers with alkyl substituents ≤C4 (four carbons) were not very potent, but did show selectivity values greater than or equal to MSI‐78. In contrast, those with alkyl substituents ≥C6 were as potent, or more potent, than MSI‐78 and in three specific cases demonstrated selectivity values similar to, or better than, MSI‐78. To understand if these polymers were membrane active, polymer induced lipid membrane disruption activities were evaluated by dye leakage experiments. Lipid composition and polymer hydrophobicity were found to be important factors for dye release.

No abstract.

Summary: Two well-characterized metallocene isotactic poly(propylene) (iPP) samples, one of high and one of low molecular weight, were blended together for studying the effects of a second component on quiescent and shear-induced crystallization. A small amount of added high molecular weight (HMW) (up to 10 wt.-%) polymer increases the quiescent crystallization rate. This was observed as a decrease in characteristic halftime of transmitted light intensity. The crystallization halftime increases again when adding more than 10 wt.-% of HMW polymer. The crystallization halftime of pre‐sheared samples decreases with increasing HMW fraction and is lowest for the HMW sample by itself. For the specific shearing conditions (γ = 600, Tx = 145 °C), wide‐angle X‐ray diffraction (WAXD) images show the presence of the gamma (γ) crystalline phase of iPP for samples containing 25 wt.‐% of HMW and higher. DSC thermograms demonstrated higher crystalline fractions with increasing HMW fraction in pre‐sheared samples.Optical micrograph of an iPP sample after quiescent crystallization at 145 °C.

The poly(hydroxy-amide) [PHA] family of polymers possess not only high temperature stability, but also form a more thermally stable polymer (polybenzoxazole) [PBO] during thermal decomposition. The synthesis occurs in solution at low temperature, preventing premature ring cyclization to PBO. The molecular structure was confirmed from 1H-, 13C-NMR, and elemental analysis. One drawback for the highly aromatic PHA is the lack of a softening temperature before the onset of ring closure to PBO. Thus, poly(methoxy-amide) [PMeOA] and random copolymers of PHA and PMeOA have been synthesized and characterized. From microcalorimetry, the peak heat release capacity values for the copolymers is typically higher than that of the pure PHA (while still much lower than most other polymers); however, differential scanning calorimetry (DSC) analysis has shown glass transition temperatures to as low as 151°C for the copolymers. Thermo-gravimetric analysis (TGA) displays a three-step degradation associated with two ring closures to PBO from PHA and PMeOA (with the release of small low-fuel molecules) and the thermal degradation of PBO. The magnitude of the weight loss associated with each step is dependant on the percent of PHA, PMeOA, and aliphatic content in the copolymer. TGA and DSC analysis of PMeOA films under isothermal conditions show degradation and demethylation (cyclization) occurring simultaneously above 300°C and FT-IR displays benzoxazole ring forming under the same condition. Fibers have been spun from the molten state of PMeOA using a Micro-compounder. Fibers spun at 320°C, with average diameter of 180 μm, show an ultimate tensile strength, elongation at break, and Young's modulus of 60 MPa, 2.2% and 3.6 GPa, respectively. Films were also made by spin-coating or solvent casting to observe the effect of cyclization on tensile properties. These films had an ultimate tensile strength and Young's modulus of 120 MPa and 3 GPa, respectively.

An in situ ultrasonic spectroscopy technique was used to study the ring-opening metathesis polymerization of dicyclopentadiene catalyzed by bis(tricyclohexylphosphine)benzylidene ruthenium dichloride. A reaction cell employing a flexible poly(ethylene terephthalate) window for pulse echo ultrasonic spectroscopy was used to monitor the polymerization. The changes in the density, wave speed, acoustic modulus, and attenuation were all simultaneously monitored. In comparison with Fourier transform infrared (FTIR) spectroscopy data, the changes in the density, velocity, and modulus only accurately measured the rate constant for the metathesis of the cyclopentyl unsaturation. The ultrasonic values were within 6% of the values determined by FTIR. The activation energy for metathesis of the cyclopentyl unsaturation was 84 kJ mol⁻¹, following first-order kinetics. Rate constants for the polymerization of the norbornyl unsaturation could not be determined by ultrasound. The gel point, vitrification, and qualitative information about the reaction rate could be determined from the change in the attenuation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1323–1333, 2003

Copolymerizations of styrene and the polyhedral oligomeric silsesquioxane (POSS)–styryl macromonomer 1-(4-vinylphenyl)-3,5,7,9,11,13,15-heptacyclopentylpentacyclo [9.5.1.1^3,9.1^5,15.1^7,13] octasiloxane have been performed with CpTiCl3 in conjunction with methylaluminoxane. Random copolymers of syndiotactic polystyrene (sPS) and POSS have been formed and fully characterized with ¹H and ¹³C NMR, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. NMR data reveal a moderately high syndiotacticity of the polystyrene backbone consistent with this use of CpTiCl3 as a catalyst and POSS loadings as high as 24 wt % and 3.2 mol %. Thermogravimetric analysis of the sPS–POSS copolymers under both nitrogen and air shows improved thermal stability with higher degradation temperatures and char yields, demonstrating that the inclusion of the inorganic POSS nanoparticles makes the organic polymer matrix more thermally robust. The polymerization activity and thermal stability are also compared with those of reported atactic polystyrene–POSS copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 885–891, 2002; DOI 10.1002/pola.10175

Ring-opening metathesis copolymerizations of cyclooctene and the polyhedral oligomeric silsesquioxane (POSS) monomer 1-[2-(5-norbornen-2-yl)ethyl]-3,5,7,9,11,13,15-heptacyclopentylpentacyclo[9.5.1.1^3,9.1^5,15.1^7,13] octasiloxane (POSS–norbornylene) were performed with Grubbs's catalyst, RuCl2(&dbond;CHPh)(PCy3)2. Random copolymers were formed and fully characterized with POSS loadings as high as 55 wt %. Diimide reduction of these copolymers afforded polyethylene–POSS random copolymers. Thermogravimetric analysis of the polyethylene–POSS copolymers under air showed a 70 °C improvement, relative to a polyethylene control sample of similar molecular weight, in the onset of decomposition temperature based on 5% mass loss. The homopolymer of POSS–norbornylene was also synthesized. This polymer had a rigid backbone according to ¹H NMR evidence of broad olefinic signals. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2920–2928, 2001

Polymer nanocomposites containing self-assembled cellulose nanocrystals (CNCs) are ideal for advanced applications requiring both strength and toughness as the helicoidal structure of the CNCs deflects crack propagation and the polymer matrix dissipates impact energy. However, any adsorbed water layer surrounding the CNCs may compromise the interfacial adhesion between the polymer matrix and the CNCs, thus impacting stress transfer at that interface. Therefore, it is critical to study the role of water at the interface in connecting the polymer dynamics and the resulting mechanical performance of the nanocomposite. Here, we explore the effect of polymer confinement and water content on polymer dynamics in CNC nanocomposites by covalently attaching a fluorogenic water-sensitive dye to poly(diethylene glycol methyl ether methacrylate) (PMEO2MA), to provide insights into the observed mechanical performance. Utilizing fluorescence lifetime imaging microscopy (FLIM), the lifetime of dye fluorescence decay was measured to probe the polymer chain dynamics of PMEO2MA in CNC nanocomposite films. The PMEO2MA chains experienced distinct regions of differing dynamics within Bouligand structures. A correlation was observed between the average fluorescence lifetime and the mechanical performance of CNC films, indicating that polymer chains with high mobility improved the strain and toughness. These studies demonstrated FLIM as a method to investigate polymer dynamics at the nanosecond timescale that can readily be applied to other composite systems.

Block polymers assemble into a variety of phase-separated morphologies based on volume fraction (φ) and interactions (χ) of the respective blocks. The arrangement of three different polymer blocks could either be a 3-arm star, with each block having one terminus attached to a common junction point or a linear A-B-C architecture. A versatile strategy is reported to synthesize a series of well-defined graft polymers that lie along the unexplored continuum between a 3-arm star and an A-B-C linear triblock polymer architecture. Using the technique of single-molecule insertion, precise control over the position of graft arm C along the B chain was achieved. A series of discrete graft polymers (PMMA-b-PS-g-PEO) with fixed φ and prescribed ω values that lie on the continuum between a 3-arm star (ω = 0) and linear triblock polymer (ω = 1) were synthesized. Morphological studies using small-angle X-ray scattering and conventional and energy-filtered transmission electron microscopy reveal the transition between lamellae, perforated lamellae, and cylindrical morphologies with systematic variation in the ω values, a trend attributed to the topological frustration and the associated χ values between the three blocks. Molecular dynamic simulations of coarse-grained models were found to predict phase diagrams that are consistent with the experimentally observed morphologies. Our results suggest that changes in ω lead to topological frustration which is an important additional new design parameter that can be used to tune the morphology of multiblock polymers in addition to φ and χ.

The regular arrangement of complementary diaminopyridine-thymine DAP-THY on alternating copolymers permits cooperative binding events and the effective formation of well-controlled micrometre-scale aggregates.

Anion exchange membranes (AEMs) contain cations that act as dipoles. The dipoles interact with each other and give rise to clustering in the AEM and this clustering can affect the ionic conductivity and mechanical properties of the polymer. Polymers designed to have dispersed cations can, when wet, have their cations cluster as the material undergoes an order-disorder transition at some temperature at which the system has enough energy to reorganize. Clustering is often unavoidable in AEMs and imposes a limit on the increase in conductivity that can be achieved by increasing IEC. Above a certain IEC AEMs do not show increased ionic conductivity only increased swelling on exposure to higher RH. Understanding these phenomena is essential to designing high performance AEMs. Here we propose an AEM based on a scalable random copolymer with rapidly deployed photo-crosslinking to lock the morphology in place to avoid cation clustering.

Anion Exchange membranes (AEMs) are being developed for a variety of applications. Among these are fuel cells and electrolyzers that require the AEM to conduct hydroxide anions. Measurement of the ionic conductivity of hydroxide is challenging because the hydroxide is a strong nucleophile and attacks polar groups in the AEM and also rapidly reacts with atmospheric CO2to form the less conductive carbonate and bicarbonate counter anions. We have developed a rigorous method to fully exchange AEMs into the hydroxide form while excluding CO2and remove all residual inorganic salt from the film prior to measurement. These measurements of the hydroxide ion conductivity coupled with self diffusion measurements of water and the similarly sized fluoride anion in these films are beginning to shed insight into how hydroxide anion transport can be maximized in state of the art AEMs.

Anion exchange membranes (AEM) are polymer electrolytes that facilitate ion transport in alkaline fuel cells and electrochemical devices. Fabrication of mechanically durable AEMs with high ionic conductivity is a challenge. Here, a copolymer of isoprene and vinylbenzyl trimethylammonium and a terpolymer of isoprene, vinylbenzyl trimethylammonium and styrene were crosslinked by various methods, and properties, including conductivity and mechanical strength, were investigated at dry and saturated conditions. Polymer chemistry and degree of crosslinking significantly influenced conductivity, swelling, and mechanical properties. The terpolymer had a higher proportion of vinylbenzyl trimethylammonium units increasing the ion exchange capacity (IEC), but membranes could still be rendered insoluble by crosslinking. The higher IEC of the terpolymer resulted in higher chloride conductivity, 20–75 mS/cm at 50°C and 95%RH, compared to 4–17 mS/cm for the copolymer at the same conditions. At dry conditions films were stiff, having Young's moduli between 100–740 MPa, but hydration caused severe softening, reducing moduli by 1–2 orders of magnitude. The severe softening effect of hydration was confirmed by dynamic mechanical analysis. The AEMs studied did not have adequate mechanical durability at hydrated conditions, additional work is needed to determine polymer chemistries and crosslinking methods that will produce robust AEMs for long-term use in fuel cells and electrochemical devices.

Extensive transport and modeling studies have been performed on a series of polymers based on the benzyltrimethylamonium cations. We have created a realistic reactive model of solvated hydroxide that has interesting properties in the polymer matrix. In ordered di-block polymers we have strong theoretical evidence for a heterogeneous distribution of water across the channel. Fluoride is used as a non-reactive surrogate for hydroxide to increase the computational efficiency of transport calculations that can be performed. In addition to these studies we are discovering new base stable processable robust polymer backbones and cations. These bulky cations seem to dramatically affect the transport properties of the anions showing a VTF rather than an Arrhenius behavior with temperature.

Extensive transport and modeling studies have been performed on a series of polymers based on vinylbenzyltrimethylamonium cations. Flouride is used as a non-reactive surrogate for hydroxide to increase the computational efficiency of transport calculations that can be performed. Interesting effects of water and residual chloride in the film have been explained. In ordered di-block polymers we have strong theoretical evidence for narrow water domains that facilitate rapid transport of anions. With this model we will be able to predict diblock polymer structures that require less water for efficient anion transport. In addition to these studies we are discovering new base stable polymer backbones and cations. A large part of this effort is dedicated to discovering new methods for the production of robust thin anion exchange membranes.

There is increasing interest in the alkaline exchange membrane (AEM) fuel cells as this device, if realized, could allow the use of inexpensive metal catalysts and the oxidation of a variety of convenient liquid fuels. While there have been some dramatic early achievements, there is still a need for a fundamental study of anion transport, cation stability and the formation of robust thin films in this area. We have undertaken a comprehensive study of anion transport and AEMs where theory is linked to well-defined model systems, both in solution and in the solid state, which are characterized using very careful environmental control such that the models can be validated and used predictively. We are also fabricating a number of structured copolymer AEMs that can be produced readily in large quantities, allowing us to understand film formation coupled with transport and stability.

There is increasing interest in the alkaline exchange membrane (AEM) fuel cells as this device, if realized, could allow the use of inexpensive metal catalysts and the oxidation of a variety of convenient liquid fuels. While there have been some dramatic early achievements, there is still a need for a fundamental study of anion transport, cation stability and the formation of robust thin films in this area. We have undertaken a comprehensive study of AEMs where theory is linked to well-defined model systems, both in solution and in the solid state, which are characterized using very careful environmental control such that the models can be validated and used predictively. We are also fabricating a number of random copolymer AEMs that can be produced readily in large quantities, allowing us to understand film formation coupled with transport and stability. Those based on perfluorinated backbones invite interesting comparisons with the analogous proton exchange membranes.