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We report on establishing the polydispersity in chemical composition (PCC) and polydispersity in monomer sequence distribution (PMSD) in random copolymers of poly(styrene-co-4-bromostyrene) (PBrxS), where x = (0.385 ± 0.035) is the mole fraction of the 4-bromostyrene units (4-BrS), prepared by electrophilic substitution of bromine in the para-position of the phenyl ring of the parent polystyrene. Upon fixing the total number of repeating units, we tune the distribution of styrene and 4-BrS segments in PBrxS by carrying out the bromination reaction on polystyrene homopolymers in different solvents. While PBrxS with relatively random comonomer distribution is prepared in 1-chlorodecane, random-blocky sequences of 4-BrS in PBrxS are achieved by carrying out the bromination reaction in 1-chlorododecane. The PCC in both copolymers is established by fractionating both polymers using interaction chromatography (IC) and determining the chemical composition of the individual fractions by neutron activation analysi...

Polystyrene-b-poly(2,2,2-trifluoroethyl acrylate)s (PS-b-PTFEAs) are a high-χ block copolymer (BCP) system possessing high potential for fabricating sub-10 nm nanoscopic patterns, however, their th...

Control over the size and functional group distribution of soft responsive hydrogel particles is essential for applications such as drug delivery, catalysis and chemical sensing. Traditionally, targeted functional group distributions are achieved with semi-batch techniques which require specialized equipment, while the preparation of size-tailored particles typically involves the use of surfactants. Herein, we present a simple and robust surfactant-free method for the modulation of size and carboxylic acid functional group distribution in poly(N-isopropylacrylamide) thermoresponsive microgels, employing reaction pH as the single experimental parameter. The varying distributions of carboxylic acid residues arise due to differences in kinetic reactivity, which are a function of the degree of dissociation of methacrylic acid, and thus of reaction pH. Incorporated charged residues induce a surfactant-like action during the particle nucleation stage, and impact the final particle size. Characterization with dynamic light scattering, and electron microscopy consistently supports the pH-tailored morphology of the microgels. A mathematical model which accounts for particle deformation on the imaging substrate also shows excellent agreement with the experimental results.

Elastomeric anion exchange membranes (AEMs) were prepared by acid-catalyzed Friedel–Crafts alkylation of the polystyrene block of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) using...

A simple approach to fabricating nanoporous structures and their functionality is demonstrated using a triblock copolymer of polystyrene-b-poly(methyl methacrylate)-b-poly(tert-butyl acrylate) (PS-b-PMMA-b-PtBA), where a continuous-type morphology is set in PS matrix to form the cylinders consisting of the PMMA and minor PtBA blocks. For directional and uniform nanochannels at the interfaces, a perpendicular orientation of cylinders was exploited near two interfaces of air/polymer and polymer/neutral substrate, sandwiching the random orientation of cylinders in the interior of the film. Nondegradative, selective swelling–deswelling process of cylindrical (PMMA-b-PtBA) blocks generates nanopores as an effective route to precisely tune the pore size. Further, a simple hydrolysis of tBA units functionalizes the nanopore surfaces and walls into poly(acrylic acid) layers. We demonstrate the pH-responsive water permeability of nanoporous membranes and their active switching with respect to biomolecules such as ...

We investigated how the reactivity of epoxide and oxetane monomers in photoinitiated cationic polymerization is strongly influenced by their ability to form intramolecular hydrogen-bonding complexe...

Aromatic rings of poly(styrene-b-(ethylene-r-butylene)-b-styrene) triblock copolymer (SEBS) were functionalized with various acid functional groups for proton exchange membrane (PEM) applications. Three different acid functional groups (fluoroalkylsulfonic acid, arylsulfonic acid, and arylphosphonic acid) were introduced into SEBS via borylation of aromatic C–H bonds and Suzuki coupling reactions. The incorporation of acid side groups selectively into the polystyrene block of SEBS created nanometer-scale phase separated morphology composed of hydrophilic and hydrophobic domains in which the morphology structures and interdomanin distances are dependent on the chemical structure of acid side chains. Despite high ion exchange capacity value, the aryl phosphonated polymer (SEBS-P) showed the lowest water uptake and significantly lower proton conductivity compared to sulfonated SEBS PEMs because of the low acidity of phosphonic acid. Compared to aryl sulfonated SEBS-S2, fluoroalkyl sulfonated SEBS-S1 showed b...

Proton-conducting superacidic polymer membranes with different fluoroalkyl sulfonate pendants attached to aromatic polymer backbones were synthesized via C–H functionalization and Suzuki coupling reactions. Variation in the chemical structures of the pendant acidic sulfonate moieties and their effects on membrane properties including water uptake, ion exchange capacity, morphology, and proton conductivity were systemically investigated. Membranes containing the short −OCF2SO3H pendant (PSU-S5) showed a smaller hydrophilic domain size and lower proton conductivity than those containing the longer pendants −OCF2CF2SO3H (PSU-S1) and −SCF2CF2SO3H (PSU-S4), likely due to the short chain’s less favorable aggregation and lower acidity. Polymer electrolyte membranes with unique branched fluoroalkyl sulfonate pendants (PSU-S6) gave larger ionic domain sizes, more uniform hydrophilic channels, and higher proton conductivity than samples with analogous linear pendant chains (PSU-S1), indicating that branched sulfona...

A chemically stable and elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), was functionalized with various benzyl- and alkyl-substituted quaternary ammonium (QA) groups for anion exchange membrane (AEM) fuel cell applications. Synthetic methods involving transition metal-catalyzed C–H borylation and Suzuki coupling were utilized to incorporate six different QA structures to the polystyrene units of SEBS. Changes in AEM properties as a result of different QA moieties and chemical stability under alkaline conditions were investigated. Anion exchange polymers bearing the trimethylammonium pendants, the smallest QA cation moiety, exhibited the most significant changes in water uptake and block copolymer domain spacing to offer the best ion transport properties. It was demonstrated that incorporating stable cation structures to a polymer backbone comprising solely C–H and C–C bonds resulted in AEM materials with improved long-term alkaline stability. After 4 weeks in...

With the combinations of diglycidyl ether diphenolate methyl ester (DGEDP-Me), a rigid high-viscosity bio-based epoxy resin and a flexible lower viscosity epoxy resin from cashew nut shell liquid (NC-514), resin viscosity was controlled and important improvements were realized in cured epoxy resin toughness relative to the neat resins. The viscosities of DGEDP-Me/NC-514 mixtures varied from 660 to 26 Pa.s, and curing was performed using stoichiometric amounts of a diamine cross-linker. Using scanning electron microscopy analysis of fractured surfaces, the cured materials were shown to be one-phase. Furthermore, all resin compositions were transparent and have one alpha transition temperature, confirming resin miscibility. Storage modulus values for cured thermosets range from 3000 to 1000 MPa, and alpha transition temperatures varied linearly (158 to 27°C) as a function of the epoxy resin composition. Oscillatory rheology at different weight percentages of the flexible and rigid epoxy resin components was used to determine the average molecular weight between cross-links which was correlated to material toughness. Relative to the neat high-viscosity resin, 1:1 wt/wt mixtures of the rigid and flexible epoxy resin components gave increases in the impact strength and mode I fracture toughness of 136 and 66%, respectively. Higher percentages of the flexible epoxy resin resulted in decreased toughness.

Zn2Al layered double hydroxides (LDHs) modified with stearic acid, oleic acid, or caproic acid were synthesized by the co-precipitation method for the compounding with poly(styrene-co-acrylonitrile) (SAN) at 0 to 6 wt% contents using a co-rotating twin screw extruder. Melt flow indices (MFI) and mechanical properties of SAN nanocomposites were measured to know the effect of organic modifier. MFI of SAN nanocomposites reinforced with stearic acid modified LDH (SA-Zn2Al LDH) were multiplied by the lubrication effect of considerably released organic modifier over 5 wt%. Mechanical properties of SAN nanocomposites showed the maximum values at the contents of organically modified LDH between 1 and 5 wt%. The optimum contents of organically modified LDHs (OLDHs) for tensile modulus were measured as 1 or 2 wt%, significantly less than the percolation threshold calculated as 4.7 wt% for an aspect ratio of 25. Except the flexural strength and notched Izod impact strength, caproic acid modified LDH (CA-Zn2Al LDH) showed the best mechanical performance. SAN nanocomposites containing oleic acid modified LDH (OA-Zn2Al LDH) showed the slightly largest values in both flexural strength and notched Izod impact strength. These results show that the strategy of organically modified LDH (OLDH) can be used to reinforce the SAN polymer without compromising mechanical properties. Copyright © 2015 John Wiley & Sons, Ltd.

Branched poly[1,4-butylene carbonate-co-terephthalate]s (PBCTs) have been synthesized by the addition of a small amount of glycerol propoxylate (1) or pentaerythritol (2) in the polycondensation of 1,4-butanediol, dimethyl carbonate, and dimethyl terephthalate. To avoid gel formation, the feed amount of 1 or 2 was carefully controlled at below 0.5 mol % for 1 and below 0.3 mol % for 2. When feed of 1 or 2 was used, a high-molecular weight melt state (Mw ∼180,000 g/mol) was reached in a total reaction time of 5.5 to 6.5 h with a yield higher than 90%. The generated PBCTs were a semicrystalline polymer (Tg ∼5 °C and Tm ∼120 °C) when the terephthalate content (F[TPA]) was 45 to 50 mol %. The crystallization rate increased with increasing F[TPA] and branch content (F[1 or 2]); PBCT composed of F[TPA] = 49 mol % and F[1] = 0.44 mol % was crystallized completely in a short time, ∼3 min, at a crystallization temperature of 50 °C. The branched PBCT exhibited more pronounced toughness in tensile test while providing the advantage of processibility at high shear rates due to the pronounced shear thinning in melt. It was also found that the branched PBCTs were biodegradable. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 914–923

Small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and high performance liquid chromatography (HPLC) experiments are performed to support that the inter-micellar distance of Pluronic cubic structures in aqueous solutions is governed by the poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblock copolymer concentration (not the overall polymer concentration) in the solutions. The “as-received (AR)” and “purified (Pure)” F108 solutions show a separate concentration dependence of body-centered cubic (BCC) lattice spacing, when the overall polymer concentration is used as a micellar packing parameter in aqueous solution. When the 22 wt% of non-micellizable polymeric impurities in the AR Pluronic F108 is taken into account, however, a universal concentration dependence of the BCC lattice spacing is observed, unifying results from both AR and Pure F108 solutions. When the PEO-PPO-PEO triblock copolymer concentration from the HPLC analysis is employed as an effective polymer concentration parameter, the universal relationship is observed to provide strong evidence that the polymeric impurities in AR F108 locate themselves in the less dense parts of the interstitial regions on the BCC lattice points, where were occupied by the triblock copolymer micelles. Although the polymeric impurities in AR F108 do not affect the actual triblock concentration dependence of the lattice spacing, they do shift the onset concentration of BCC micellar ordering. In the Pure F108, the onset of BCC packing occurs at the point where the nearest-neighbor radius (R nn) in the BCC lattice is approximately equal to the hydrodynamic radius (R h), indicating that lattice formation begins upon “hydrodynamic contact” between micelles. In the AR F108, the onset of packing occurs when R nn/R h is approximately 0.9, indicating that, in the presence of the polymeric impurities, micelles must be forced together beyond the point of hydrodynamic contact for the BCC packing.

CE-SSCP analysis is a well-established DNA separation method that is based on variations in mobility caused by sequence-induced differences in the conformation of single-stranded DNA. The resolution of CE-SSCP analysis was improved by using a Pluronic polymer matrix, and it has been successfully applied in various genetic analyses. Because the Pluronic polymer forms a micellar cubic structure in the capillary, it provides a stable internal structure for high-resolution CE-SSCP analysis. We hypothesized that formation of micellar cubic structure is influenced by the end hydroxyl group of the Pluronic polymer, which affords structural stability through hydrogen bonding. To test this hypothesis, the hydroxyl group was halogenated to eliminate the hydrogen bonding without disturbing the polarity of polymer matrix. CE-SSCP resolution of two DNA fragments with a single base difference was significantly worse in the halogenated polymer matrices due to band broadening. The viscoelastic properties of control (which has hydroxyl group), chlorinated, and brominated F108 solution upon heating were also investigated by rheological experiments, and we found that gelation was significantly associated with resolution. In this series of experiments, the effect of the hydroxyl group in Pluronic polymer matrix on separation resolution of CE-SSCP analysis was demonstrated.

Pluronic F108 block copolymers have shown a great promise to achieve the desirable high resolution in the conformation-sensitive separation of ssDNA using CE-SSCP. However, fundamental understanding of the structures and properties of Pluronic matrix affecting the resolution is still limited. Unlike conventional gel-forming homopolymers, Pluronic F108 block copolymers are amphiphilic macromolecules consisting of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers, which are capable of forming a highly ordered micellar structure in aqueous solution. In this study, we have performed a series of experiments by blending different types of Pluronic polymers to control the formation of micelles and to study the correlation between separation and rheological characteristics of Pluronic gels affecting the resolution of CE-SSCP. Our experiments have been specifically designed to elucidate how the micellar structure affects the resolution of CE-SSCP upon altering the size uniformity and constituent homogeneity of the micelles. Our results suggest that uniformly sized micelle packing is the primary structural feature of Pluronic gel matrix for the high-resolution separation, while the size and constituent of the micelle themselves need to be considered as secondary factors.

We report the synthesis and characterization of novel block copolymer (BCP) materials for the directed self-assembly (DSA) nanolithography applications. Specifically, the poly(t-butyl acrylate) (PtBA) block in the styrenic block copolymers have been chemically modified to a fluorinated block for the enhancement of the BCP χ-parameters. dPSb- PtBA had been first synthesized by anionic polymerization to prepare a well-defined BCP precursor with narrow polydispersity for the fluorination of PtBA block. Then, the precursor BCP was chemically modified by transalcoholysis of the PtBA-block with 2,2,2-trifluoroethanol. This strategy offers the advantage of flexibility and controllability to tailor the χ-parameter, while maintaining the narrow molecular weight distribution of the BCP materials for the advanced lithography applications. The transmission electron microscopy/small angle x-ray scattering (TEM/SAXS) characterization results of the modified BCP consisting of poly(fluoroalkylate) and PS supported the development of highly ordered lamellar domains in bulk.

A new scalable method for large scale purification of Pluronic block copolymers has been developed using a slurry of cyano(CN)-modified silica particles and Pluronic block copolymers in a solution. We have taken advantage of the competitive adsorption of polymers onto nanoporous CN-modified silica particles in solution to purify polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymers from as-received (AR) Pluronic samples, such as F108, F127 and F68. Interaction chromatography and size exclusion chromatography revealed that significant levels of low molecular weight (MW) impurities exist in AR Pluronics. We found that more than 20 wt.% impurities exists in AR F108 and AR F127, while the purified PEO-PPO-PEO triblock copolymers contained less than 2 wt.% of the low MW impurities after using the silica slurry method. In the case of AR F68, which contains about 9 wt.% impurities, it is possible to completely remove the low MW impurities. A multiple injection interaction chromatography technique has been employed to reveal the surface displacement of pre-adsorbed low MW impurities by the triblock copolymers in solution. By tuning the solvent quality, this report finally highlights that the impurities can be effectively removed in laboratory for a large scale purification using the silica slurry. For example, using about 10 g of the bulk silica packing material, it was possible to obtain 1 g of purified triblock copolymers.

The kinetics of the cationic ring-opening polymerizations of epoxide monomers were controlled through the use of supramolecular proton complexes. α,ω-Diglycidyl oligoethylene oxides bearing multiple ethyleneoxy spacer groups form metastable supramolecular proton complexes with strong Bronsted acids generated either by the photolysis of onium salts or by their redox reactions with reducing agents. Trapping of the Bronsted acids by in situ complex formation results in a delay of the onset of cationic ring-opening. However, once polymerization begins, the epoxide groups of the monomer are very rapidly consumed resulting in characteristically highly exothermic autoaccelerated polymerization reactions. Crown ethers can also form supramolecular complexes with hydronium ions derived from the reaction of protonic acids with water and these complexes can be used to modify the kinetic behavior of the cationic ring-opening thermal and photopolymerizations of a variety of epoxide monomers. The ring size of a crown et...

The effects of solution temperature and molecular weight on the rheological responses of poly(vinyl alcohol) (PVA) semidilute solutions (13 g/dL- 19 g/dL) in dimethyl sulfoxide (DMSO) have been studied using PVA with two different number-average degrees of polymerization (Pn): 1700 and 4000. For the rheological experiments using dynamic shear, the PVA solution with a Pn of 1700 showed rather simple Newtonian fluid behaviour, whereas that with Pn of 4000 exhibited non-Newtonian shear thinning behaviour. Steady shear rheology experiments suggested that the lower Pn PVA solutions were Newtonian fluids, which is consistent with the dynamic shear rheology results. However, an abrupt decrease of shear viscosity at high shear rates was observed for the higher Pn PVA solutions at lower temperatures, such as 30 °C and 50 °C. At higher temperatures of 70 °C and 90 °C, the higher molecular weight PVA solutions exhibited simple shear thinning behaviour without any further complications of flow instability. The fact that temperature plays a critical role in controlling the observed flow instability of the PVA solutions in DMSO strongly suggests that there exist enhanced inter-chain interactions by hydrogen bonding of PVA chains beyond the chain entanglements, particularly for the higher Pn PVA semidilute solutions at low temperatures. Therefore, it is important to consider both chain entanglements and hydrogen bonding interactions in order to process PVA solutions without causing undesirable flow instability.

Although CE-SSCP analysis combined with 16S ribosomal RNA gene-specific PCR has enormous potential as a simple and versatile pathogen detection technique, low resolution of CE-SSCP causes the limited application. Among the experimental conditions affecting the resolution, the polymer matrix is considered to be most critical to improve the resolution of CE-SSCP analysis. However, due to the peak broadening caused by the interaction between hydrophobic moiety of polymer matrices and DNA, conventional polymer matrices are not ideal for CE-SSCP analysis. A poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) (PEO-PPO-PEO) triblock copolymer, with dynamic coating ability and a propensity to form micelles to minimize exposure of hydrophobic PPO block to DNA, can be an alternative matrix. In this study, we examined the resolution of CE-SSCP analysis using the PEO-PPO-PEO triblock copolymer as the polymer matrix and four same-sized DNA fragments of similar sequence content. Among 48 commercially available PEO-PPO-PEO triblock copolymers, three were selected due to their transparency in the operable range of viscosity and PEO(137)PPO(43)PEO(137) exhibited the most effective separation. Significant improvement in resolution allowed discrimination of the similar sequences, thus greatly facilitated CE-SSCP analysis compared to the conventional polymer matrix. The results indicate that PEO-PPO-PEO triblock copolymer may serve as an ideal matrix for high-resolution CE-SSCP analysis.

In this article, we have investigated a temperature-rise fractionation procedure for poly(3-hexyl thophene) (P3HT) and poly(3-octyl thophene) (P30T) that provides well-defined molecular weight (MW) fractions with improved molecular weight distributions (MWD) when compared with Soxhlet extraction. This process involves dispersing the material over C18-boned silica stationary phase in a jacketed column and using incremental rises in column temperature (T col ) to gradually improve solvent quality and selectively dissolve higher molecular weight samples with a narrow polydispersity (PDI). Fractionation of P3HT with ΔT col = 5 °C in methylene chloride (MC) yielded 7 fractions ranging from M p of 20 to 53 kg/mol with an average PDI of 1.80 compared with a mother sample of 3.10. Predominant recovery of P3HT was acquired for fractions with T col > 20 °C (30 wt %). Subsequent separation of P30T in methylene chloride, with a reduced ΔT col of 3 °C per fraction, due to increased solubility from the longer alkyl chain, generated 8 fractions with a weight range of M n = 22 to 57 kg/mol with an mean PDI of 1.23 with the mother sample having PDI = 2.34, demonstrating the tunability of this method.

Liquid chromatography at the critical condition (LCCC) is a high performance liquid chromatography (HPLC) technique that lies between size exclusion chromatography and adsorption-based interaction chromatography, where the elution of polymers becomes independent of polymer molecular weight. At LCCC, the balance between the entropic exclusion and the enthalpic adsorption interactions between polymers and stationary phases results in the simultaneous HPLC elution of polymers regardless of molecular weight. Using C18-bonded silica chromatographic columns with 5 μm particle size and different average pore size (diameter = 300 A, 120 A, 100 A, and 50 A), we report (1) the thermodynamic significance of LCCC conditions and (2) the influence of column pore size on the determination of critical conditions for linear polymer chains. Specifically, we used mixtures of monodisperse polystyrene samples ranging in molecular weight from 162 to 371,100 g/mol and controlled the temperature of the HPLC columns at a fixed composition of a mobile phase consisting of 57(v/v)% methylene chloride and 43(v/v)% acetonitrile. It was found that, at the fixed mobile phase composition, the temperature of LCCC (TLCCC) is higher for C18-bonded chromatographic columns with larger average pore size. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2533–2540, 2009

Interaction chromatography has been employed to validate that adsorption of poly[styrene-co-(4-bromostyrene)] (PBr(x) S) random copolymers, where x denotes the mole fraction of 4-bromostyrene (4-BrS) in PBr(x) S in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co-monomer sequence distribution in PBr(x) S.

Structural and chemical changes of aged terrace-like pentacene films have been investigated using grazing-incidence X-ray diffraction (GIXD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The electrically active pentacene nanolayers on the dielectric substrate are susceptible to the oxidative degradation upon aging in air because the near-substrate grain boundaries between the terrace-like domains are well exposed to light and air during aging. GIXD and AFM for pentacene films have been used to elucidate the structural changes, locally initiated at the edges of terraced layers of pentane films upon aging-related oxidative degradation. XPS has revealed the chemical nature of pentacene oxidation upon aging, suggesting the development of hydroxyl and carbonyl groups during aging with light in air. Finally, we have investigated how the structural and chemical degradation of the aged pentacene films reduces the charge mobility and on-off ratio of organic field-effect transistors exposed to light and air.

The effects of solution processing and thermal annealing on thin film morphology and crystalline structures of regioregular poly(3-hexyl thiophene) (RR P3HT) are studied in terms of molecular weight (M{sub w}). Using grazing-incidence X-ray diffraction, {pi}-conjugated planes in drop-cast films from chloroform solutions are found to be preferentially oriented parallel to the substrates regardless of M{sub w}. However, the mesoscale nanocrystalline morphology of the drop-cast films is significantly affected by M{sub w}, exhibiting a distinctive morphological transition from short nanorods to long nanofibrils above a critical number-averaged M{sub w} ({approx} 3.6 kDa). This is probably due to the change in a conformation change from an extended-chain to a folded-chain, as M{sub w} of RR P3HT increases. In contrast, spin-casting of high M{sub w} RR P3HT produces less ordered films with a lower crystallinity and mixed parallel/perpendicular orientations of {pi}-conjugated planes. The crystallinity and parallel -conjugated orientation of RR P3HT in spin-cast films could be improved by thermal treatments at high-temperatures either (1) above the glass transition temperature or (2) above the melting temperature of RR 3PHT followed by recrystallization upon cooling under vacuum. However, the charge mobility of the spin-cast films for a field-effect transistor application is still lower than thatmore » of the drop-cast films. This would be attributed to the chain oxidation and the development of distinct grain boundaries between RR P3HT nanofibrils during the thermal treatments.« less

Catalyst formation kinetics of a ferrocene-containing homopolymer, polyferrocenylethylmethylsilane (PFEMS), is investigated as it relates to the catalysis of single walled carbon nanotubes (SWNTs) through a chemical vapor deposition (CVD) process. The formation and efficiency of the PFEMS-based iron catalyst is compared with that of the corresponding polystyrene (PS)-b-PFEMS diblock copolymer. The PFEMS homopolymer contains 23 wt % iron, while PS-b-PFEMS, with a 25 vol % PFEMS content, is only 6% iron. Despite its lower iron content, spin-cast PS-b-PFEMS films on SiO 2 /Si substrates produce more active iron sites than spin-cast PFEMS films during CVD growth of SWNTs. This is related to the self-assembly of the block copolymer, where PFEMS domains are well dispersed in the PS matrix, which degrades at a CVD temperature of 920°C to leave catalytically active elemental iron behind. On the contrary, the pure PFEMS films contain a high percentage of iron and silicon, which tend to transform into ceramic-coated iron at this high temperature, thus rendering the iron inactive towards SWNT growth.

The effects of radiation-induced modifications on the thermal stability and phase transition behaviour of composites made of 1% pristine or ion irradiated single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) are reported. Thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), Raman spectroscopy and electron spin resonance (ESR) were used to investigate the radiation-induced functionalization of carbon nanotubes and to assess the effect of ionizing radiation on the adhesion between macromolecular polymer and carbon nanotubes. Irradiation was used to introduce defects in a controlled way solely within pristine nanotubes before composite synthesis. The addition of irradiated SWNTs to a polymer matrix was found to enhance thermo-oxidative stability and phase transition behaviour. Further, ESR studies demonstrate the electronic interaction through charge transfer between filler and matrix. These results could have immense applications in nanotube composite processing. Based on the experimental data, a model for the interaction between polymeric chains and carbon nanotubes is proposed.

The cyclolinear polycarbosilane, (poly(1-hexyl-1,3-ditolyl-1,3-disilacyclobutane) poly(HDTDSCB)), which has tolyl groups attached to the main chain Si atoms, was prepared by ADMET polymerization with the second-generation Grubbs catalyst, and 10%, 5%, and 2% of the tolyl groups were brominated by reactions with N-bromosuccinimide. A series of well-controlled poly(methyl methacrylate) (PMMA) anions of 2.5K, 5K, and 10K molecular weight were introduced via the “grafting onto” strategy at low temperature to the randomly 10%, 5%, and 2% brominated poly(HDTDSCB), respectively, without any lithiation or ring opening of the disilacyclobutane in the main chain. Because of side reactions initiated by the PS anion under similar conditions, a “grafting from” strategy by ATRP was employed to yield the corresponding poly(HDTDSCB)-g-PS random copolymers. The product poly(HDTDSCB)-g-(PMMA or PS) random copolymers were purified by using total adsorption−desorption interaction chromatography, which involves selective adso...

Dendronized polyferrocenylsilanes were synthesized by a substitution reaction of reactive poly(ferrocenylchloromethylsilane) with monodendrons with a focal hydroxy group. The resulting dendronized polymers were studied by 1H NMR, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). To facilitate the direct visualization of single polymer chains by atomic force microscopy (AFM), an interaction chromatography technique (IC) was used to fractionate the polydisperse polymers to separate the high molecular weight dendronized PFSs. AFM studies of the fractionated high molecular weight PFSs revealed a spherical cocoon for the single chains of the dendronized polymer as well as elongated single-chain structures. The cocoon of the dendronized PFS could be interesting as a unimolecular micelle with the transition-metal-rich core which is isolated by the dense outer layer of the dendrons.

The correlation between near-surface morphology and tack behavior of poly(styrene-b-butadiene-b-styrene) triblock copolymer (SBS)/rosin ester films was investigated using probe tack tests, transmission electron microscopy and small-angle X-ray scattering. The SBS/rosin films with rosin composition between 10 and 20 wt% rosin, prepared by slow evaporation of toluene during solvent casting, exhibited uniform near-surface morphology of lamellae oriented parallel to the surface. However, due to the limited solubility of rosin in the PS domains, the rosin started to phase-separate from the PS domains at 15 wt%, and formed fully separated micron-sized domains above 20 wt% rosin. The probe tack force of the SBS/rosin films increased steadily when the near-surface domain orientation changed from perpendicular cylinder to parallel lamellae on addition of rosin. Specifically, for a given lamellar morphology and surface orientation, macrophase separation of rosin plays a critical role in determining the tack properties of SBS/rosin films.

We report effects of proton irradiation on thermal oxidation of single-walled carbon nanotubes (SWNTs). Following 400 keV proton irradiation to doses of 1013–1017 cm−2, thermal oxidation of SWNTs was conducted at temperatures 200–700 °C. The mass of SWNTs during oxidation was monitored with thermogravimetric analysis (TGA) and ion-beam-induced structural modifications in nanotubes were characterized with Raman spectroscopy. Proton irradiation leads to enhanced thermal stability of nanotubes, as indicated by increased values of the temperature (Tmax) for maximum oxidation rate, e.g. Tmax ∼ 495 °C for pristine SWNTs and Tmax ∼ 525 °C for SWNTs irradiated to the dose of 1 × 1015 cm−2. The activation energy for oxidation increases gradually from 1.13 ± 0.01 eV for pristine SWNTs, to ∼1.25 ± 0.02 eV for the largest dose of 5 × 1016 cm−2. Based on the correlation between TGA and Raman data, we discuss possible mechanisms for the observed effects of proton irradiation on SWNT thermal oxidation.

Well-defined polymer brushes grafted onto silica nanoparticles were prepared by reversible addition−fragmentation chain transfer polymerization (RAFT). A versatile RAFT agent, 4-cyanopentanoic acid...

The crazing and fracture behaviors of glassy-glassy block copolymers were investigated for polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymers that had similar overall molecular weights but different poly (methyl methacrylate) (PMMA) molar fractions. A liquid chromatography technique was applied to separate as-synthesized PS-b-PMMA [(1) weight-average molecular weight (M w ) = 94,000 g/mol and PMMA molar fraction = 0.35 and (2) M w = 65,000 g/ mol and PMMA molar fraction = 0.28] into three fractions with different chemical compositions. With a copper-grid technique, the fracture behaviors of 0.5-μm-thick PS-b-PMMA films were studied as a function of the applied strain. For the higher M w PS-b-PMMA samples, the median strains at crazing and fibril breakdown increased with an increase in the PMMA molar fraction from 0.24 to 0.46, corresponding to an increase in the chain entanglements in the PMMA domains. In contrast, for the lower M w samples, the two values were not significantly changed even when the PMMA molar fraction was varied from 0.16 to 0.35. M w of the minor component in PS-b-PMMA played a critical role in controlling the fracture behaviors of the block copolymers. Specifically, M w /M e of the minor component (where M e is the molecular weight between entanglements) had to be roughly larger than 2 for the block copolymers to sustain sufficient strains before fracture.

Block copolymer ordering in thin films on a preferentially wetting flat substrate is studied using a polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer, which forms PMMA cylinders in bulk. Tapping-mode AFM and cross-sectional TEM were employed to characterize the thin film ordered structure of the PS-b-PMMA on a flat silicon surface with native oxide that is preferentially wetted by PMMA blocks. The PS-b-PMMA in thin film develops hexagonally perforated layer (HPL), which is different from its cylindrical bulk morphology. The HPL structure of PS-b-PMMA exhibits islands and holes at the surface, which persists up to the film thickness as high as 6L0. Surface-induced reorganization of the block copolymers on PMMA-preferring flat surface may be responsible for the formation of the layerlike nonbulk structure of HPL, which has been templated from the flat surface and propagated into a multilayered HPL films.

Regioregular poly(3-hexyl thiophene) (RR P3HT) is drop-cast to fabricate field-effect transistor (FET) devices from different solvents with different boiling points and solubilities for RR P3HT, such as methylene chloride, toluene, tetrahydrofuran, and chloroform. A Petri dish is used to cover the solution, and it takes less than 30 min for the solvents to evaporate at room temperature. The mesoscale crystalline morphology of RR P3HT thin films can be manipulated from well-dispersed nanofibrils to well-developed spherulites by changing solution processing conditions. The morphological correlation with the charge-carrier mobility in RR P3HT thin-film transistor (TFT) devices is investigated. The TFT devices show charge-carrier mobilities in the range of 10 - 4 ∼10 - 2 cm 2 V - 1 s - 1 depending on the solvent used, although grazing-incidence X-ray diffraction (GIXD) reveals that all films develop the same π-π-stacking orientation, where the -axis is normal to the polymer films. By combining results from atomic force microscopy (AFM) and GIXD, it is found that the morphological connectivity of crystalline nanofibrils and the -axis orientation distribution of the π-π-stacking plane with respect to the film normal play important roles on the charge-carrier mobility of RR P3HT for TFT applications.

With the aim of enhancing the field-effect mobility by promoting surface-mediated two-dimensional molecular ordering in self-aligned regioregular poly(3-hexylthiophene) (P3HT) we have controlled the intermolecular interaction at the interface between P3HT and the insulator substrate by using self-assembled monolayers (SAMs) functionalized with various groups (–NH2, –OH, and –CH3). We have found that, depending on the properties of the substrate surface, the P3HT nanocrystals adopt two different orientations—parallel and perpendicular to the insulator substrate—which have field-effect mobilities that differ by more than a factor of 4, and that are as high as 0.28 cm2 V–1 s–1. This surprising increase in field-effect mobility arises in particular for the perpendicular orientation of the nanocrystals with respect to the insulator substrate. Further, the perpendicular orientation of P3HT nanocrystals can be explained by the following factors: the unshared electron pairs of the SAM end groups, the π–H interactions between the thienyl-backbone bearing π-systems and the H (hydrogen) atoms of the SAM end groups, and interdigitation between the alkyl chains of P3HT and the alkyl chains of the SAMs.

Mutations in Cu/Zn superoxide dismutase (SOD) are associated with familial amyotrophic lateral sclerosis (FALS), a neurodegenerative disease that is characterized by the selective death of motor neurons. Despite the genetic association made between the protein and the disease, the mechanism by which the mutant SOD proteins become toxic is still a mystery. Using wild-type SOD and three pathogenic mutants (A4V, G37R, and G85R), we show that the copper-induced oxidation of metal-depleted SOD causes its in vitro aggregation into pore-like structures, as determined by atomic force microscopy. Because toxic pores have been recently implicated in the pathogenic mechanism of other neurodegenerative diseases, these results raise the possibility that the aberrant self-assembly of oxidatively damaged SOD mutants into toxic oligomers or pores may have a pathological role in FALS.