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Wireless transduction of light into mechanical work manifested as shape-changing surfaces, adaptive structures, or actuators is a topic of considerable recent interest. In the work reported here, the photomechanical responses of a new series of crosslinked azobenzene-functionalized polyimides prepared with increasing backbone rigidity over a range of crosslinker concentrations are examined. The baseline properties of the materials were characterized with X-ray diffraction, thermal analysis, and photomechanical examination including cantilever bending experiments and tensile tests. Increasing the rigidity of the backbone repeat unit reduces the magnitude of the shape change (observed as cantilever deflection) but increases the magnitude of photogenerated stress (in tensile tests). The promise of these materials as wireless actuators was examined in photoinitiated snap-through experiments.

Polymer-grafted inorganic nanoparticles are being developed for a diverse array of applications, ranging from drug delivery to multifunctional composites. In many instances, performance of these core-shell hybrids is limited by relatively broad distributions of size and composition, as well as the presence of impurities, such as unattached polymer chains. Herein, further synthetic improvements, and associated characterization techniques, to enhance the fraction of the grafted polystyrene shell on silica hybrid nanoparticles are discussed. We found that during surface-initiated atom transfer radical polymerization (SI-ATRP) from the silica nanoparticles, thermal self-initiation of styrene produces unattached polymer chains. Size exclusion chromatography afforded a facile approach to quantify the mass of the unattached polymer, and provide a substantial refinement to estimates of chain graft density beyond traditionally-used approaches, such as thermogravimetry. This fraction of unattached polymer is still present even after post-polymerization work-up via precipitation and re-dissolution. Removal necessitates additional procedures, such as high speed centrifugation. Selection of a lower polymerization temperature, in concert with a more reactive Cu complex, significantly reduces the amount of unattached polystyrene impurity. The improved polymerization conditions and post-polymerization purification provide more refined polystyrene-grafted silica nanoparticles to clarify structure-property relationships of these core-shell hybrids.

High-performance aerospace-grade polyimides such as CP2 fulfill many important roles in a wide range of applications. A thorough understanding of the polymer matrix’s physiochemical properties is an important consideration when developing polymer nanocomposite materials. In this work, we report the dielectric properties of polyimide CP2 including the primary and two secondary dipole relaxations, and their thermal characteristics by way of temperature variable impedance spectroscopy (10 −2 to 10 6 Hz, −40 to 225 °C). Special emphasis has been placed on detailing the characteristic phenomena near CP2′s glass transition (199 °C). The consequences of residual DMAc solvent on CP2′s overall loss and relaxation characteristics are also discussed.

A series of poly(ether ketone) copolymers were prepared by nucleophilic aromatic polymerization reactions of the AB monomer 4-fluoro-4′-hydroxybenzophenone, 1 , and the AB 2 monomer bis(4-fluorophenyl)-(4-hydroxyphenyl)phosphine oxide, 2 , in the presence of 3 or 5 mol% of a highly reactive core molecule, tris(3,4,5-trifluorophenyl)phosphine oxide (B 3 ), 4 . All of the copolymers prepared in the presence of a core molecule were sufficiently soluble in N -methylpyrrolidinone, NMP, to allow the determination of their molecular weights and polydispersity indices, PDIs. Number-average molecular weights, M n s, of 3200–6800 Da were determined and the PDI values ranged from 1.41 to 4.07. The M n was controlled by the mol% of 4 present in the reaction mixture with higher molar percentages leading to lower M n values. Lower reaction temperatures and lower ratios of AB/AB 2 monomers afforded copolymers with lower PDI values. As expected, the crystallinity of the samples decreased with an increasing AB 2 content or an increase in PDI. The copolymers also exhibited excellent thermo-oxidative stability with a number of samples suffering 5% weight losses at temperatures, in air, well in excess of 450 °C.

As a continuation of previous work involving synthesis of an allyl-functionalized hyperbranched polyimide, AT-PAEKI, we have studied the use of this reactive polymer as a modifier of bisphenol-A based bismaleimide resin (BPA-BMI). This was pursued in anticipation of improvements in processability as well as physical properties including glass transition temperature, elastic modulus, and fracture toughness. Apparent miscibility, indicated by optical clarity with a single Tg, was observed for compositions containing up to 16 wt% AT-PAEKI. Additionally, we observed complete suppression of monomer crystallization and a slight increase in the overall cure exotherm. By rheological characterization, blends containing 4 wt% AT-PAEKI were found to feature a dramatic (65-fold) reduction in the viscosity minimum during heating. Dynamic mechanical analysis (DMA) showed that the addition of 2, 4, 8 wt%. AT-PAEKI increases the cured modulus by approximately 10% from a base value of 3.4 GPa, while adding 16 wt% AT-PAEKI decreases the modulus slightly to 3.3 GPa. DMA also revealed that the cured glass transition temperature increases monotonically with the addition of AT-PAEKI. Fracture toughness was gauged using the single edge notched beam methodology to yield the critical stress intensity factor, KIC. Our results showed a modest toughening effect (from 0.48 to 0.55 MPa m 1/2 ) upon the

Direct covalent attachment of amorphous and semicrystalline polyetherketones onto the surface of either an as-received multi-walled carbon nanotube (MWNT) or a vapor-grown carbon nanofiber (VGCNF) in polyphosphoric acid (PPA) with optimized P2O5 content resulted in uniform grafting of polyetherketones to these carbon nanoscale materials. Soxhlet extraction experiment, the spectra from FT-IR spectroscopy and the clear images from high-resolution transmission electron microscopy showed that the covalent attachment is effective in uniformly coating the PEK grafts on the surfaces of both MWNT and VGCNF. Additionally, a drastic increase in solution viscosity due to the formation of giant molecules was monitored during polymerization. As such, the resulting nanocomposites were easily fabricated via a simple compression molding technique. The alignment possibility of MWNT and VGCNF grafted with semicrystalline PEK in these thermoplastic nanocomposites via solution fiber spinning was also demonstrated.

The synthesis and isolation of 6-phenylethynyl picolinic acid (PEPCA; IUPAC name: 6-(2-phenylethynyl)pyridine-2-carboxylic acid) was first demonstrated when Acinetobacter sp. strain F4 was used to biotransform diphenylacetylene to the ring-fission product that underwent facile ring closure to form PEPCA in the presence of ammonium ions. Here, the structure and properties of PEPCA were confirmed by comparison with those of PEPCA that was chemically synthesized. In the chemical route, commercially available 6-bromopicolinic acid was first converted to methyl 6-bromopicolinate using methyl iodide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The resulting methylester was coupled with phenylacetylene by the palladium-catalyzed reaction to yield methyl 6-phenylethynyl picolinate, which was then hydrolyzed by sodium carbonate to afford PEPCA. Both enzymatically and chemically synthesized PEPCA were used to prepare its thermally reactive bis(benzylester) and bis(amide) derivatives. Thus, three phenylethynyl-terminated bis(amide) derivatives were synthesized by treating PEPCA with 1,3-phenylenediamine, 4,4′-oxydianiline or 4,4′-(hexafluoroisopropylidene)dianiline via dicyclohexylcarbodiimide (DCC)-mediated amidation. The bis(benzylester) derivative was prepared from PEPCA and α,α′-dibromo-p-xylene. All the intermediates and final products were characterized by FT-IR, NMR, MS and elemental analysis. The thermal properties of PEPCA and the reactive derivatives were characterized by DSC and TGA. The exothermic peaks of three bis(amide) derivatives were at least 20–40 °C lower than typically reported for the phenylethynyl compounds. Lowered reaction temperatures observed for the thermally-induced free radical polymerization of phenylethynyl groups were attributed to the strong electron-withdrawing capability of the pyridine moiety. Bis(amide) derivatives exhibited excellent thermal stability after previously cured at 300 °C for 30 min and 350 °C for 30 min.

A series of poly(ether ketone) copolymers were prepared by nucleophilic aromatic polymerization reactions of 4-fluoro-4′-hydroxybenzophenone, 2, in the presence of varying percentages of ABn monomers based on a triarylphosphine oxide platform, 1a (2F), 1b (4F), and 1c (6F), where A=OH and B=F. As expected, the crystallinity of the samples decreased with an increasing ABn content. However, the tetrahedral geometry of the phosphine oxide-based ABn monomers proved to be much more efficient at lowering the melt temperature of the copolymers than was the corresponding ketone-based ABn monomer, 3,5-bis(4-fluorophenylbenzoyl)phenol, 4, that possesses a structure more similar to that of 2. Polymerization of 2 in the presence of as little as 5 mol% of bis-(3,4,5-trifluorophenyl)-(4-hydroxyphenyl)phosphine oxide, 1c (6F), afforded a completely amorphous polymer with a glass transition temperature of 168 °C that was soluble in hot NMP and DMSO. The copolymers also exhibited excellent thermoxidative stability with a number of samples displaying 5% weight loss temperatures, in air, well in excess of 500 °C.

We recently described an improved method to synthesize poly(ether-ketones) or PEKs. It utilized an optimized mixture of polyphosphoric acid (PPA) and P 2 O 5 that is not only milder, less corrosive and less expensive than super-acid media, but also can play the multiple roles of solvent, Friedel–Crafts catalyst and dehydrating agent. The as-prepared PEKs from such a highly viscous reaction medium displayed unexpected, thermally induced relaxation exotherms regardless of the amorphous or semi-crystalline nature of polymer. This thermal behavior was not observed for the formally identical polymers [viz. p PEK or poly(oxy-1,4-phenylenecarbonyl-1,4-phenylene] which is normally semi-crystalline) that were separately prepared in a much less viscous mixture of methanesulfonic acid and P 2 O 5 (Eaton's reagent) or N -methyl-2-pyrrolidinone (NMP). Such an observation was first made when both samples of p PEKs were subjected to the same thermal history and the thermal relaxation exotherms were observed only for the p PEK sample that was prepared in PPA/P 2 O 5 medium. Further confirmation of viscosity-and-shear-induced strain stored in the as-synthesized PEKs was provided by a systematic annealing study with differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) analysis and Fourier-transform infrared spectroscopy (FT-IR). Based on these data, p PEK was successfully compression-molded in the temperature range of 230–250 °C which is more than 100 °C below its melting temperature.

Anisotropic homopolymerization of 2,5-dihydroxyterephthalic acid (DHTA) and 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT.2HCl), and copolymerization of DHTA, terephthalic acid and DABDT.2HCl in polyphosphoric acid (PPA), afforded high molecular weight rigid-rod polymer and copolymers, with two hydroxyl groups as pendants per repeat unit. In PPA, the lyotropic liquid crystalline behaviour of the homopolymer was distinctly affected by the polymerization temperature. Spectroscopic evidence strongly suggested a completely planar and ribbon-like structure, the consequence of the strong intramolecular hydrogen bonds between the OH moieties and the N atoms of the nearby benzothiazole units. The homopolymer also exhibited the unusual capability, characteristic of BBL-type ladder polymers, to form directly from its precipitate an aggregated film which displayed little or no shrinkage when dried. Anisotropic dopes of the homopolymer (dihydroxy-polybenzothiazole (PBZT)) and certain dihydroxy-PBZT/PBZT copolymers were spun into fibres with typical tensile properties for modified PBZT polymers, but marginal compressive strength (4–30 ksi (1 ksi = 6.9 MPa) for homopolymer and 16–61 ksi for the copolymers). The intrinsic conductivity for the as-spun fibre of the homopolymer was 2.2 × 10−7 S cm−1 and that for heat-treated (435°C) fibre was 5.6 × 10−8 S cm−1.

The first example of ionic molecular composites, i.e. the formation of rigid-rod molecular composites via ionic interactions between the polyelectrolyte host and the reinforcing rigid-rod polymer, was provided by the physical blend of poly(2-acrylamido-2-methylpropanesulphonic acid) (HAMPS homopolymer) and poly(p-phenylene benzobisthiazole) (PBZT). HAMPS homopolymer was formed in situ from its sodium salt form (NaAMPS), which is commercially available. A 52 48 ( w / w ) PBZT/HAMPS homopolymer blend was prepared by co-dissolving the components in methanesulphonic acid. Upon precipitation in cold water, the molecular composite was obtained as an orange-yellow fibre, which became red when it was dry. This solid-state chromatic variability is reversible and was observed when the blend (polymer pulp or coagulated film) was immersed in a variety of organic solvents. In addition, coagulated film showed relatively little lateral shrinkage after vacuum drying at 110°C overnight and no phase-separated morphology was detected by scanning electron microscopy within 500 A resolution.

A new concept for the processing and fabrication of rigid-rod molecular composites aiming at the elimination or minimization of phase separation is proposed. This approach calls for a coil-like aromatic polyisoimide which is soluble and compatible with an amorphous matrix polymer or thermosettable oligomer and can undergo facile transformation to the corresponding rigid-rod polyimide in solid composite state, thus imparting the inherently high strength/high modulus properties to the final form. To this end, various synthetic routes were explored to obtain para -diamines which could afford high molecular weight and aprotic-solvent-soluble polyisoimides upon polymerization with pyromellitic dianhydride (PMDA). Four such polyisoimides were prepared, with their inherent viscosities ranging from 0.25 to 1.89 dl g −1 in dimethylacetamide at 30°C. Facile thermally induced isoimide-imide conversion was demonstrated by solid-state (film) Fourier transform infrared spectroscopy. A preliminary evaluation of the compatibility of the polyisoimide/matrix resin was made. In one instance, a film prepared from the polyisoimide derived from PMDA and 3,3′,5,5′-tetramethylbenzidine (TMB) showed no visually detectable phase separation.