This study explores the role of segmental solubility of regioregular poly(3-octylthiophene) (rr-P3OT) on chain organization and its photophysical properties. In good solvent chlorobenzene (CRB), rr-P3OT chain adopts an extended conformation, allowing long conjugation length of π-electrons. Cyclohexane is a good solvent for octyl side chain but a poor solvent for the thiophene backbone. The selective segmental interactions of rr-P3OT with this solvent induce conformational change of the polymer. Addition of cyclohexane into the CRB solution leads to chain coiling, which in turn causes significant decrease of the conjugation length. Absorption and photoluminescence spectra of the rr-P3OT in cyclohexane exhibit a blueshift of about 16 nm compared to those of the CRB solution. The change of chain conformation is also detectable by monitoring the variation of quantum yield upon increasing cyclohexane ratio. The quantum yield drops from 0.17 ± 0.01 to 0.11 ± 0.01 when the extended rr-P3OT chain transforms into coiled conformation. Hexane is a nonsolvent for rr-P3OT due to its relatively low solubility parameter. The addition of hexane into rr-P3OT solution in cyclohexane forces dense packing of thiophene rings within the coiled chain. An intrachain aggregation occurs in this system, leading to the appearance of three distinct redshift peaks in absorption spectra and the drastic drop of quantum yield. Correlation between the growth of redshift peaks and the decrease of quantum yield is clearly observed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013

Molecular parameters such as interchain/intrachain aggregation and individual chain conformation affect the properties of conjugated polymers significantly. In this study, the conformational change of regioregular poly(3-octylthiophene) (rr-P3OT) is induced using cyclohexane and hexane as poor solvents. When the extended rr-P3OT chain in chlorobenzene transforms into coiled conformation in cyclohexane, the decrease of conjugation length is comparable to the shortening of 6 to 9 thiophene units. In hexane, the dense packing of thiophene units causes intrachain aggregation, resulting in the increase of conjugation length.

The work focuses on the synthesis and layer by layer (LbL) assembly of oligoallylamine and phosphonated oligoallylamine. To this aim, the synthesis of oligoallylamine and the phosphonated form have been done by free radical polymerization in aqueous media. First, radical polymerization of acid salt of allylamine was performed. This charged polymer could not be characterized using classical analytical techniques such as size-exclusion chromatography and matrix-assisted laser desorption/ionisation-time of flight mass spectroscopy due to presence of cations. This work demonstrated the interest of capillary electrophoresis (CE) to analyze charged oligomers, using very small amounts of samples. Entangled polymer solution CE was used as a size-based separation technique for the characterization of the molar mass distribution using indirect ultraviolet detection and calibration based on vinyl pyridine standards. Phosphorus-containing oligoallylamines having a number-average molar mass of 1600 g mol⁻¹ and a 2.3 polydispersity index were obtained. When combined using the LbL approach, prepared polymers showed an exponential growth regime as demonstrated by Fourier transform infrared spectroscopy measurements. Furthermore, thermogravimetric analyses of the LbL-assembled polymers showed an extraordinary thermal and thermo-oxidative stability. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Layer by layer (LbL) assemblies have been used to produce new flame retardants with charged polymers. Oligoallylamines were obtained by radical polymerization and characterized by a new technique of capillary electrophoresis then alternatively coated with phosphonated oligoallylamines like original polymers with zwitterions functions. When combined using the LbL approach, assembled polymers exhibited an exponential growth; the final assembly showed an extraordinary thermal and thermo-oxidative stability.

Polyisoprene-block-poly(vinyl trimethylsilane) (PI-b-PVTMS) block copolymers having different isoprene contents are successfully chemically modified and characterized by proton nuclear magnetic resonance spectroscopy (¹H-NMR), Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. Gas transport properties of the initial block copolymers and their derivatives modified via hydrosilylation and hydrogenation are measured. The modified block copolymers show higher permeabilities for O₂ and H₂ than the unmodified block copolymers while maintaining similar O₂/N₂ and H₂/N₂ selectivities. Hydrosilylation and hydrogenation of block copolymers with a low isoprene content result in a permeability increase for O₂ and H₂ of 15 to 40%, respectively. Similarly, for block copolymers with high isoprene contents, increases in permeabilities up to 125% are observed compared to initial PI-b-PVTMS. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Polyisoprene-block-poly(vinyl trimethylsilane) copolymers having different isoprene content are successfully modified via hydrosilylation and hydrogenation and characterized by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The modified block copolymers show higher permeabilities for O₂ and H₂ than the unmodified block copolymers, while maintaining similar O₂/N₂ and H₂/N₂ selectivities. The increase in permeability after modification is related to the changing chemical and repulsive interactions between blocks resulted in different morphology and the increasing fractional free volume.

Polymerization of a self-assembled 1-dodecyl-3-propargylimidazolium bromide ionic liquid (IL) yields a nanostructured ionic polyacetylene. A 1:1 aqueous mixture of the amphiphilic IL produces an ordered lyotropic mesophase that adopts a hexagonal perforated lamellar structure. Rh (I)-mediated polymerization of the assembled mixture yields a hexagonal modulated lamellar structured polymer. FTIR spectroscopy reveals that the polymer was self n-doped. The polymer was fractioned into three components with the majority product, possessing an intermediate molecular weight that is soluble in polar organic solvents. In methanol, the optical band gap of the main fraction was determined to be 2.38 eV and was nonemissive. The solution-processable polymer was airbrush sprayed onto glass substrates to give a liquid-crystalline, lamellar structured semiconductive film (7.02 × 10⁻⁵ S cm⁻¹). The polymer resisted oxidation (degradation) upon storage in air as monitored by vibrational spectroscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013

An ionic liquid monomer that can be self-assembled and captured through transition metal initiated polymerization into a nanostructured, yet solution processable, ionic polyacetylene is synthesized. The polymer is an ionic conductor and an electronic semiconductor, and its insolubility in water and resistance to oxidative degradation coupled with solution processability employing polar organic solvents makes it a viable material for potential use as a bioelectrode.

Solid electrolyte membranes based on alkali-doped polyvinyl alcohol (PVA) and PVA/carbon nanotubes (PVA/CNTs) are used in direct borohydride fuel cells (DBFCs). As 0.05 wt % of CNT is incorporated into the PVA matrix, the polymer crystallinity is decreased from 42.4% to 38.0% and the fractional free volume increases from 2.48% to 3.53%. The KOH-doped PVA/CNT exhibits the highest ionic conductivity of 0.0805 S cm⁻¹, because of the increased polymer free volume (which promotes vehicular OH⁻ transport) and the presence of CNT (which serves as the conducting microchannels). Sodium borohydride (NaBH₄) in NaOH solution and potassium borohydride (KBH₄) in KOH mixture are fed into the cells. The power density of the KBH₄-based DBFC is almost twice that of the NaBH₄-based DBFC (184 vs. 92 mW cm⁻²) due to less KBH₄ permeability through the films, higher conductivity of the KOH-doped PVA composites than those in the sodium counterpart, and probably higher electro-catalytic kinetics. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Carbon nanotubes (CNTs) are functionalized with polyvinyl alcohol (PVA) and a small amount (0.05 wt %) of functionalized CNT is blended with PVA solution to form PVA/CNT composite. The alkaline-doped PVA and PVA/CNT are tested in fuel cells fed with NaBH₄/NaOH or KBH₄/KOH solution. The resulting peak power density in an alkaline KBH₄ fuel cell loaded with PVA/CNT/KOH electrolyte is much higher than those achieved with Nafion and other electrolytes reported in the literature.

Poly(phenylene oxide) block and random copolymers are synthesized by oxidative polymerization of 2,6-dimethylphenol and 2,6-diphenylphenol for potential alkaline exchange membrane application. The copolymers are functionalized on the methyl substituted repeat units through a two-step process to produce pendent quaternary ammonium cationic groups. The amount of quaternary ammonium cations and the ion exchange capacity are quantified through titration measurements. Ionic conductivity of the copolymer membranes is measured by electrochemical impedance spectroscopy. Block copolymers show increased bromide conductivity at higher ion exchange capacities compared with the random copolymer analogs. The bromide conductivity for a block copolymer film with an ion exchange capacity of 1.27 mequiv/g reaches 26 mS/cm at 90 °C and 95% relative humidity. The hydroxide conductivity for the same film was measured to be 84 mS/cm at 80 °C and 95% relative humidity. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

The morphology and phase separation of polymers within a fuel cell membrane plays a large role in its performance. This work compares block and random poly(phenylene oxide) copolymers in relation to their conductivity and water uptake as a function of ion exchange capacity. The block copolymers perform significantly better than the random analogs. The high conductivity suggests that the morphology is improved for ion conduction in the block copolymers.

In this study, new alkaline exchange membranes were prepared from the perfluorinated 3M ionomer with various quaternary ammonium cations attached with sulfonamide linkage. The degree of functionalization varied depending on the cation species, resulting in different ion exchange capacities (IECs), 0.33–0.72 meq g⁻¹. There was evidence of polymer degradation when the films were exposed to hydroxide, and hence all membrane characterization was performed in the chloride form. Conductivity was dependent on cation species and IEC, E_a = 36–59 kJ mol⁻¹. Diffusion of water through the membrane was relatively high 1.6 × 10⁻⁵ cm² s⁻¹ and indicated restriction over a range of diffusion times, 6–700 ms. Water uptake (WU) in the membranes was generally low and the hydration level varied based on cation species, λ = 6–11. Small-angle scattering experiments suggested ionic aggregation, 37–42 Å, independent of cation species but slight differences in long-range order with cation species. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Anion exchange membranes (AEMs) must have high hydroxide conductivity and be chemically stable for the lifetime of the fuel cell. Proton exchange membrane fuel cells have demonstrated that hydration and polymer morphology can significantly effect ion conduction in the membrane. Understanding the role of water and morphology on ionic transport in AEMs is important to direct the development of high performing membranes.

Block copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium tetrafluoroborate) (PS-b-[PVBTMA][BF₄]) were synthesized by sequential monomer addition using atom transfer radical polymerization. Membranes of the block copolymers were prepared by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS-b-[PVBTMA][BF₄] materials via SAXS revealed the formation of spherical, cylindrical, and lamellar morphologies. Block copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium hydroxide) (PS-b-[PVBTMA][OH]) were prepared as polymeric alkaline anion exchange membranes materials by ion exchange from PS-b-[PVBTMA][BF₄] with hydroxide in order to investigate the relationship between morphology and ionic conductivity. Studies of humidity [relative humidity (RH)]-dependent conductivity at 80 °C showed that the conductivity increases with increasing humidity. Moreover, the investigation of the temperature-dependent conductivity at RH = 50, 70, and 90% showed a significant effect of grain boundaries in the membranes against the formation of continuous conductive channels, which is an important requirement for achieving high ion conductivity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Fundamental investigations about the relationship between morphology and conductivity in alkaline anion exchange membranes made from well-defined block copolymers are sparse. The synthesis, morphology, and conductivity of polystyrene-b-poly(vinyl benzyl trimethylammonium tetrafluoroborate) (PS-b-[PVBTMA][OH]) are investigated. The block copolymers self-assemble into spherical, cylindrical, and lamellar microstructures. The nonlinearly increasing conductivity at high humidity with increasing ion exchange capacity results from the inherent nature of the microstructures. An inverse relationship between conductivity and temperature is attributed to the effect of swelling, or shrinkage, of the polycation segment and to the existence of grain boundaries.

An alkaline exchange membrane (AEM) based on an aminated trimethyl poly(phenylene) is studied in detail. This article reports hydroxide ion conductivity through an in situ method that allows for a more accurate measurement. The ionic conductivities of the membrane in bromide and carbonate forms at 90 °C and 95% RH are found to be 13 and 17 mS cm⁻¹ respectively. When exchanged with hydroxide, conductivity improved to 86 mS cm⁻¹ under the same experimental conditions. The effect of relative humidity on water uptake and the SAXS patterns of the AEM membranes were investigated. SAXS analysis revealed a rigid aromatic structure of the AEM membrane with no microphase separation. The synthesized AEM is shown to be mechanically stable as seen from the water uptake and SAXS studies. Diffusion NMR studies demonstrated a steady state long-range diffusion constant, D_∞ of 9.8 × 10⁻⁶ cm² s⁻¹ after 50–100 ms. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

The study of hydroxide ion conductivity in an inert atmosphere is important to obtain an accurate measurement. Otherwise, the hydroxides react rapidly with ambient carbon dioxide to form carbonates and bicarbonates. In this study, an in situ method with an environment chamber is used to investigate hydroxide ion conductivity. The results demonstrate a high conductivity for the hydroxide form of the membrane at similar experimental conditions.

Anion exchange membranes comprised of a poly(phenylene) backbone and one of five different cationic head-groups are prepared, briefly characterized, and tested for stability in 4 M KOH at 90 °C. The two membranes with resonance-stabilized cations (benzyl pentamethylguanidinium and benzyl N-methylimidazolium) show large (>25%) decreases in both conductivity and ion exchange capacity (IEC) after just one day of testing. The membrane with benzyl trimethylammonium cations shows a 33% loss of conductivity (14% decrease in IEC) after 14 days while the membrane with trimethylammonium cations attached by a hexamethylene spacer shows the least degradation: a 5% loss of conductivity over 14 days with no accompanying loss in IEC. A similar membrane which has a six-carbon spacer and a ketone adjacent to the phenyl ring shows much lower stability, suggesting that the ketone takes part in degradation reactions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Interest is growing in hydroxide-ion-conducting anion exchange membrane fuel cells (AEMFCs), since they avoid high-cost noble metal catalysts as used in proton exchange membrane fuel cells. Here, a series of anion exchange membranes based on a poly(phenylene) backbone and with various attached cations are studied. Whilst all five membranes have water uptake and ionic conductivity values that are promising for use in AEMFCs, the replacement of a benzylic methylene spacer with a hexamethylene spacer results in greater stability.

The concomitant appearance of crystallites and nanocavities under uniaxial strain is investigated by X-ray scattering in a model natural rubber system. The nanocavities appear after crystallization and only when the true stress is above a critical cavitation stress σ_Cav. The presence of crystallites alone does not influence the calculation of the void volume fraction ϕ_void. The nanocavities formed are 20–50 nm in size with a constant aspect ratio. The presence of filler shifts the critical crystallization extension ratio λ_Cry, λ_Cav, and σ_Cav to lower values. The clear correlation between σ_Cav and the crystallinity at the onset of cavitation χ_C(λ_Cav) implies that the crystallites take most of the mechanical loading thus delaying the cavitation in the amorphous phase. Under cyclic loading, nanocavitation is significant only in the first loading and in the successive loadings if the extension ratio is above its maximum historical value. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1125–1138

The concomitant appearance of crystallites and nanocavities under uniaxial strain is investigated by X-ray scattering in filled natural rubber. 20–50 nm elliptical nanocavities, appear after crystallization and only when the true stress is above a critical cavitation stress σ_Cav. The clear correlation between σ_Cav and degree of crystallinity at the onset of cavitation χ_Cry(λ_Cav) implies that the crystallites take most of the mechanical loading thus delaying the cavitation in the amorphous phase.

The influence of temperature and moisture activity on the viscoelastic behavior of fluorinated membranes for fuel cell applications was investigated. Uncrosslinked and crosslinked ethylene tetrafluoroethylene (ETFE)-based proton-conducting membranes were prepared by radiation grafting and subsequent sulfonation and their behavior was compared with ETFE base film and commercial Nafion^® NR212 membrane. Uniaxial tensile tests and stress relaxation tests at controlled temperature and relative humidity (RH) were carried out at 30 and 50 °C for 10% < RH < 90%. Grafted films were stiffer and exhibited stronger strain hardening when compared with ETFE. Similarly, both uncrosslinked and crosslinked membranes were stiffer and stronger than Nafion^®. Yield stress was found to decrease and moisture sensitivity to increase on sulfonation. The viscoelastic relaxation of the grafted films was found to obey a power-law behavior with exponent equal to −0.04 ± 0.01, a factor of almost 2 lower than ETFE, weakly influenced by moisture and temperature. Moreover, the grafted films presented a higher hygrothermal stability when compared with their membranes counterparts. In the case of membranes, a power-law behavior at RH < 60% was also observed. However, a markedly different behavior was evident at RH > 60%, with an almost single relaxation time exponential. An exponential decrease of relaxation time with RH from 60 s to 10 s was obtained at RH ≥ 70% and 30 °C. The general behavior of grafted films observed at 30 °C was also obtained at 50 °C. However, an anomalous result was noticed for the membranes, with a higher modulus at 50 °C when compared with 30 °C. This behavior was explained by solvation of the sulfonic acid groups by water absorption creating hydrogen bonding within the clusters. A viscoelastic phase diagram was elaborated to map critical conditions (temperature and RH) for transitions in time-dependent behavior, from power-law scaling to exponential scaling. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1139–1148

Proton exchange membranes for fuel cell applications were developed based on fluorinated, radiation grafted, and crosslinked polymers. These polymers exhibit intricate hygro-thermo-mechanical properties. A phase diagram was developed to map critical transitions in viscoelastic behavior and to investigate the influence of the grafted and crosslinked chemistry on these transitions. A deeper understanding of the stability of such membranes under different conditions should facilitate the construction of more robust fuel cells.

The viscoelastic properties of thin polystyrene (PS) films depend on confinement, as it can modify the molecular dynamics affecting the glass transition. In the recent past, the authors have investigated the region next to the free interface by means of an atomic force microscope suitably modified to monitor the indentation of a tip into a film during a given lapse of time while applying a constant load. Herein, to explore the interface with the substrate, the authors report on experiments in which PS brushes grafted to native silicon oxide were used. It was found that the film wettability on brushes and H-terminated silicon can be highly improved when compared with native silicon oxide. In addition, the glass transition temperature of thin films increases up to the bulk value in the case of film/brush combinations with high molecular weight or films with high molecular weight on H-terminated silicon. Data are discussed according to hypotheses such as residual solvent presence, interface free volume, and molecular mechanical coupling. These observations can be of great interest for nanotechnological applications, especially in those instances where one needs to tailor the temperature dependence of viscoelastic properties of thin films. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1149–1156

The temperature dependence of the viscoelastic properties of thin polystyrene (PS) films is monitored via the indentation of an atomic force microscope tip into films prepared on native silicon oxide, H-terminated silicon, and PS brushes. For film/brush combinations with Mw above the critical value for the occurrence of molecular entanglement or for films with the same Mw values on H-terminated silicon, the Tg of thin films becomes comparable with the bulk value. Data are discussed in terms of residual solvent presence, interfacial free volume, and molecular entanglement.

Positron annihilation lifetime spectroscopy (PALS) is a common technique used to characterize the porosity of polymers. Here, we expand its use to the study of ordered nanoporous polymer monoliths. Polystyrene (PS) monoliths with aligned cylindrical pores ranging in diameters from 15 to 35 nm were examined. Such large pores push the boundaries of the PALS technique. To achieve robust measurement, our system used larger detectors than those typically used for monolithic polymer samples. This was done to improve data rates while sacrificing timing resolution. Pore sizes determined using PALS were consistent with measurements made using small angle x-ray scattering. In addition, PALS was able to detect the collapse of the pores when the monolithic sample was heated above the T_g of PS. Because PALS measurements are not sensitive to the nature of the order within the structure nor are they, sensitive to the open or closed nature of the pores this technique could be expanded to a variety of other sample types. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1157–1161

Positron lifetime spectroscopy is extended to analyze the pore structure of nanoporous polymers prepared from ordered triblock polymer precursors.

The crystallinity of polyelectrolytes has long been known to affect their ionic conductivity, but the effects of water of hydration on polyelectrolyte structure are not commonly studied. Here, polymer complexes consisting of poly(ethylene oxide) (PEO) with magnesium chloride (anhydrous MgCl₂, MgCl₂·4H₂O, and MgCl₂·6H₂O, respectively) have been prepared by a mixed-solvent method. Fourier transform-infrared measurements indicate each magnesium chloride salt can coordinate with PEO to form a complex. The structures of (PEO)_xMgCl₂·4H₂O and (PEO)_xMgCl₂·6H₂O complexes are similar, whilst the structure of (PEO)_xMgCl₂ complex is different to both. Wide angle X-ray diffraction studies indicate in each polymer complex system the crystallization of PEO is depressed by the interaction of magnesium cation with the ether oxygen of PEO. PEO in (PEO)_xMgCl₂ and (PEO)_xMgCl₂·4H₂O are shown to be amorphous, but in (PEO)_xMgCl₂·6H₂O it is crystalline. Polar optical microscopy images indicate in each PEO/magnesium chloride system the crystalline morphology clearly changes with the increase of magnesium salt content. The reason for the formation of the spherulites with special morphology are the strong interaction between magnesium cation and ether oxygen of PEO, and the different evaporation rates of ethanol and chloroform in mixed solvent. A better understanding of the effects of hydration on polyelectrolyte crystallinity can help in improving their use in a variety of applications. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1162–1174

The structure and crystallinity of polyelectrolytes has long been known to affect their ionic conductivity, but the effects of water of hydration on polyelectrolyte structure are not commonly studied. Here, the structure of the complex formed in PEO/anhydrous MgCl₂ is shown to be significantly different to those of the complexes formed in PEO/hydrated MgCl₂, indicating the “crystal water” of the metal salts strongly affects the complex structure in polymer electrolytes.

New multi-stimuli responsive cationic copolymers based on N-acryloyl-N′-ethyl piperazine (AcrNEP) and N-isopropylacrylamide (NIPAM) were prepared by thermal free-radical solution polymerization in dioxane at 75 °C. The chemical composition of the copolymers was determined by ¹H NMR spectroscopy and was found that the copolymers were slightly rich in NIPAM content than that of AcrNEP. The reactivity of the two monomers for the copolymerization reaction was evaluated by the extended Kelen-Tüdös method. The distribution of monomer sequence in the copolymer chain was estimated using the terminal copolymerization model. The maximum tendency to alternation (∼ 70%) was at 60 mol % of AcrNEP in the monomer feed. The copolymers were readily soluble in water at room temperature at all compositions and exhibited well-defined lower critical solution temperature (LCST) phenomenon. The influence of various stimuli such as pH, temperature, simple inorganic salts, and surfactants on the LCST of the copolymers was studied in detail. Simple inorganic salts such as sodium chloride, sodium bromide, and sodium sulfate showed a salting-out effect while sodium iodide showed a salting-in effect. The salting-out coefficient of the salts were calculated using the Sestchenow method, and the salting trend followed the order SO₄²⁻ > Cl⁻ > Br⁻ > I⁻. The divalent salt was more effective in lowering the LCST than the monovalent salts. The cationic surfactant hexadecyl trimethylammonium bromide at concentrations above the critical micelle concentration caused a gradual increase in the LCST of the copolymer solutions. The intrinsic viscosity and light scattering behavior of the copolymers in water and in sodium chloride solutions were studied in detail. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1175–1183

A new cationic polymer, poly(N-acryloyl-N'-ethylpiperazine-co-N-isopropylacrylamide), is reported to be sensitive to multiple external stimuli such as changes in pH, temperature, salt, and surfactants. The polymer exhibited a sharp and well-defined lower critical solution temperature (LCST) because of its coil-to-globule transition. Polymerization behavior and the influence of multiple stimuli on the LCST of polymer solutions are studied in detail. This understanding could be used to tune the polymer's behavior for applications such as controlled gene delivery.

Chrysotile nanotubes (ChNTs) were synthesized under hydrothermal conditions. These synthetic nanotubes crystallographically and morphologically mimic the nanofibrils of natural white asbestos but they are considerably shorter. ChNTs containing polyimide nanocomposites were prepared by a solution mixing/casting method. Oxygen and water vapor barrier of the nanocomposite films were tested and related to the amount, dispersion, and orientation of the nanotubes. The dispersion and orientation of the nanotubes were examined by transmission electron microscopy (TEM). The nanotubes were nanodispersed and oriented in the plane of the film in the nanocomposites with up to 4.5% (vol/vol) of ChNTs leading to a gradual increase of the gas barrier. The lowest gas permeability was 60% smaller than that for the pristine polyimide film. However, with the onset of nanotube micro aggregation at larger ChNTs loadings the nanotube dispersion and orientation were compromised and oxygen barrier was reduced. The efficacy of nanotubes to enhance polymer gas barrier was discussed and compared with that by nanoplatelets. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1184–1193

Chrysotile nanotubes (ChNTs) containing polyimide nanocomposites were prepared by solution mixing/casting method. The nanotubes were nanodispersed and oriented in the plane of the film in the nanocomposites with up to 4.5% (vol/vol) of ChNTs leading to a gradual increase of the gas barrier. The lowest gas permeability was 60% smaller than that for the pristine polyimide film. However, with the onset of nanotube micro aggregation at larger ChNTs loadings the nanotube dispersion and orientation were compromised and oxygen barrier was reduced. The efficacy of nanotubes to enhance polymer gas barrier was discussed and compared with that by nanoplatelets.