Thermoreversible Gelation of Poly(ether ether ketone)

Solutions of poly­(ether ether ketone) in dichloroacetic acid have been shown to form monolithic, thermoreversible gels at temperatures ranging from 10 to 140 °C. A phase diagram was constructed over broad concentration and temperature ranges, and the phase boundary suggests an upper critical solution temperature (UCST) behavior. Furthermore, poly­(ether ether ketone) (PEEK) gels were solvent-exchanged with water to form hydrogels and subsequently lyophilized to form PEEK aerogels. The PEEK aerogels of density 0.2 g/mL were found to be highly porous and composed of uniform 200 nm morphological features. The crystal structure of the PEEK hydrogels and aerogels was found to be identical to that of melt-crystallized PEEK. The mechanical properties of the PEEK aerogels (in compression) were found to be superior to conventional silicate aerogels of comparable density. This report is the first example of a monolithic, thermoreversible gel of PEEK and the first demonstration of PEEK hydrogels and aerogels

Blocky Sulfonation of Syndiotactic Polystyrene: A Facile Route toward Tailored Ionomer Architecture via Postpolymerization Functionalization in the Gel State

Blocky sulfonated syndiotactic polystyrene (SsPS) copolymers were produced using a recently developed postpolymerization functionalization procedure conducted in the gel state. The thermal properties and crystallization behavior of a matched set of blocky and random SsPS copolymers containing 3 and 10 mol % sulfonate groups were compared using differential scanning calorimetry (DSC), which shows that the blocky functionalization architecture displays a much faster rate of crystallization even at low sulfonate contents and a higher crystallizability at high sulfonate contents. The glass transition temperature for gel-state-functionalized copolymers was found to be independent of sulfonic acid content above 4% sulfonation, consistent with behavior observed in previous studies of sodium styrene­sulfonate block copolymers. Small-angle X-ray scattering (SAXS) from the blocky copolymer indicates that the sulfonated units are distributed within the amorphous interlamellar domains. Wide-angle X-ray diffraction (WAXD) shows that the blocky architecture facilitates the formation of the β form polymorph of sPS

Blocky Ionomers via Sulfonation of Poly(ether ether ketone) in the Semicrystalline Gel State

Blocky sulfonated poly­(ether ether ketone) (SPEEK) ionomers were synthesized by postpolymerization functionalization in the gel state. Matched sets of blocky and random SPEEK with ion contents between 3 and 11 mol % were prepared, and the thermal transitions and crystallization kinetics were examined using differential scanning calorimetry (DSC). At similar ion contents, the blocky SPEEK exhibited higher crystallizability and faster crystallization kinetics than random SPEEK. Reduced scattering contrast in the USAXS/SAXS/WAXD analysis of the blocky SPEEK copolymer membranes, relative to the random analogues, suggested that the ionic aggregates in blocky SPEEK were distributed in close proximity to the crystalline domains. Despite similar water uptake values for the low ion content random and blocky SPEEK membranes, the blocky SPEEK exhibited higher proton conductivities than their random analogues. At significantly higher ion contents (45 mol %), the blocky SPEEK membranes remained semicrystalline, showed controlled water uptake, and exhibited a 2.5 times higher conductivity over that of the amorphous, random analogues. Moreover, these new blocky, semicrystalline SPEEK membranes were found to exhibit a proton conductivity that was comparable to that of the benchmark 1100 EW Nafion

Nucleobase Self-Assembly in Supramolecular Adhesives

Novel acrylic monomers functionalized with nucleobase-containing units (adenine and thymine) were prepared upon aza-Michael addition and successfully copolymerized with <i>n</i>-butyl acrylate. At a content of 7 mol %, adenine-containing units self-assembled into needle-like microstructures within amorphous polymer matrices as shown with atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD); thymine-containing units did not aggregate into distinct morphologies even to 30 mol %. Upon blending, thymine- and adenine-containing statistical copolymers associated into a thermodynamically stable complex, which was physically cross-linked through adenine–thymine base pairing. The molar fractions of the nucleobase monomer, nucleobase stacking interactions, and complementary hydrogen bonding principally influenced self-assembly. Additionally, the nucleobase-functionalized polyacrylates exhibited tunable adhesive and cohesive strength

Synthesis and Characterization of Polysulfone-Containing Poly(butylene terephthalate) Segmented Block Copolymers

A facile synthetic approach to segmented polysulfone-containing polyesters affords a versatile family of high-temperature thermoplastics with tunable thermomechanical properties. End-capping of phenol-terminated polysulfone (PSU) using ethylene carbonate generated telechelic oligomers with primary alcoholic functionality. Melt transesterification of dimethyl terephthalate and 1,4-butanediol in the presence of PSU oligomers yielded high molecular weight segmented block copolymers with alternating PSU and poly­(butylene terephthalate) (PBT) sequences. Systematic variation in PSU incorporation resulted in tunable PBT segment length and accompanying thermal properties. DSC and SAXS elucidated a miscible, amorphous PSU and PBT phase, and PBT crystallinity remained below an 80 wt % incorporation of PSU. Dynamic mechanical analysis (DMA) revealed a crystallinity-dependent plateau regime above the copolymers glass transition temperature (<i>T</i>_g), while SAXS and WAXD confirmed a semicrystalline morphology below 80 wt % PSU. Incorporation of PSU segments significantly affected the crystallization and thermomechanical properties of PBT, and as a result these copolymers offer impact as chemically resistant, high-temperature thermoplastics due to their crystallinity, thermal stability, and high-temperature operating window

Influence of Zwitterions on Thermomechanical Properties and Morphology of Acrylic Copolymers: Implications for Electroactive Applications

<i>n</i>-Butyl acrylate-based zwitterionomers and ionomers containing 3-[[2-(methacryloyloxy)ethyl](dimethyl)ammonio]-1-propanesulfonate (SBMA) and 2-[butyl(dimethyl)amino]ethyl methacrylate methanesulfonate (BDMAEMA MS), respectively, were synthesized using conventional free radical polymerization. Size-exclusion chromatography confirmed the molecular weights of the copolymers exceeded the critical molecular weight between entanglements (<i>M</i>_e) for poly(<i>n</i>-butyl acrylate). Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM) revealed that zwitterionomers promoted more well-defined microphase separation than cationic analogues. Dynamic mechanical analyses (DMA) of the copolymers showed a rubbery plateau region due to physical cross-links between charges for zwitterionomers only. Since SBMA and BDMAEMA MS have very similar chemical structures, we attributed improved microphase separation and superior elastomeric performance of the zwitterionomers to stronger association between covalently tethered charged pairs

RAFT Synthesis of ABA Triblock Copolymers as Ionic Liquid-Containing Electroactive Membranes

2-(Dimethylamino)­ethyl acrylate (DMAEA) imparts versatile functionality to poly­[Sty-<i>b</i>-(<i>n</i>BA-<i>co</i>-DMAEA)-<i>b</i>-Sty] ABA triblock copolymers. A controlled synthetic strategy minimized chain transfer reactions and enabled the preparation of high-molecular-weight ABA triblock copolymers with relatively narrow PDIs between 1.39 and 1.44 using reversible addition–fragmentation chain transfer (RAFT) polymerization. The presence of tertiary amine functionality and their zwitterionic derivatives in the central blocks of the triblock copolymers afforded tunable polarity toward ionic liquids. Gravimetric measurements determined the swelling capacity of the triblock copolymers for ionic liquids (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm TfO) and 1-ethyl-3-methylimidazolium ethylsulfate (EMIm ES). A correlation of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small-angle X-ray scattering (SAXS) results revealed the impact of ionic liquid incorporation on the thermal transitions, thermomechanical properties, and morphologies of the triblock copolymers. IL-containing membranes of DMAEA-derived triblock copolymers and EMIm TfO exhibited desirable rubbery plateau moduli of ∼100 MPa and electromechanical actuation to a 4 V electrical stimulus. Maintaining the mechanical ductility of polymer matrices while increasing their ion-conductivity is paramount for future electroactive devices

Synthesis of Polysulfone-Containing Poly(butylene terephthalate) Segmented Block Copolymers: Influence of Segment Length on Thermomechanical Performance

A facile synthesis of hydroxyethyl-functionalized poly­(ether sulfone) (PESu) oligomers permitted subsequent melt transesterification into segmented block copolymers with poly­(butylene terephthalate). The unique solubility of the PESu oligomers in the melt with 1,4-butanediol and dimethyl terephthalate enabled a systematic study of segment length on thermomechanical properties of the resulting block copolymers. ¹H NMR spectroscopy revealed a compositional dependence on the average segment length of the PBT. Additionally, the concert of NMR spectroscopy, DSC, and DMA highlighted critical segment lengths for crystallization and phase separation. In agreement with a relatively constant <i>T</i>_m and phase separation observed with DSC and DMA, respectively, small-angle X-ray scattering identified a compositionally independent lamellar thickness, while the amorphous layer thickness increased with PESu incorporation. As a result, the complementary analytical techniques provided an understanding of the morphological influence on the thermomechanical behavior of an unprecedented family of high-<i>T</i>_g, semicrystalline, segmented block copolymers

Imidazolium-Containing ABA Triblock Copolymers as Electroactive Devices

Two-step reversible addition–fragmentation chain transfer (RAFT) polymerization and two subsequent postpolymerization modification steps afforded well-defined ABA triblock copolymers featuring mechanically reinforcing polystyrene outer blocks and 1-methylimidazole-neutralized poly­(acrylic acid)-based central blocks. Size exclusion chromatography and ¹H NMR spectroscopy confirmed predictable molecular weights and narrow distributions. The ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIm]­[OTf]) was incorporated at 30 wt % into polymeric films. Thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis determined the thermomechanical properties of the polymers and polymer–IL composites. Atomic force microscopy, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) determined surface and bulk morphologies, and poly­(Sty-<i>b</i>-AA­(MeIm)-<i>b</i>-Sty) exhibited a change from packed cylindrical to lamellar morphology in SAXS upon IL incorporation. Electrochemical impedance spectroscopy determined the in-plane ionic conductivities of the polymer–IL membranes (σ ∼ 10^–4 S/cm). A device fabricated from poly­(Sty-<i>b</i>-AA­(MeIm)-<i>b</i>-Sty) with 30 wt % incorporated IL demonstrated mechanical actuation under a low applied voltage of 4 V

Ultrathin Chitin Films for Nanocomposites and Biosensors

Chitin is the second most abundant biopolymer and insight into its natural synthesis, enzymatic degradation, and chemical interactions with other biopolymers is important for bioengineering with this renewable resource. This work is the first report of smooth, homogeneous, ultrathin chitin films, opening the door to surface studies of binding interactions, adsorption kinetics, and enzymatic degradation. The chitin films were formed by spincoating trimethylsilyl chitin onto gold or silica substrates, followed by regeneration to a chitin film. Infrared and X-ray photoelectron spectroscopy, X-ray diffraction, ellipsometry, and atomic force microscopy were used to confirm the formation of smooth, homogeneous, and amorphous chitin thin films. Quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange experiments showed these films swelled with 49% water by mass. The utility of these chitin films as biosensors was evident from QCM-D and surface plasmon resonance studies that revealed the adsorption of a bovine serum albumin monolayer