Grafting of aldehyde structures to single‐walled carbon nanotubes for application in phenolic resin‐based composites

Grafting of aldehyde structures to single‐walled carbon nanotubes (SWNTs) has been carried out to endow the nanotubes with appropriate wettability. The results of Fourier transform infrared (FTIR) spectroscopy, ultraviolin‐visible‐near infrared (UV‐VIS‐NIR) spectroscopy, and Raman spectroscopy provide the supporting evidence of aldehyde structures covalently attached to SWNTs. The improved wettability of aldehyde‐functionalized SWNTs (f‐SWNTs) was demonstrated by their good dispersion in organic medium, namely, ethanol and phenolic resin. The prospective covalent bonding between aldehyde structures on the surfaces of f‐SWNTs and phenolic resin makes it possible to prepare an integrated composite with the enhanced‐interfacial adhesion. The f‐SWNT composites, therefore, show much higher average values of dσ/dW_CNT and dE/dW_CNT (i.e., tensile strength and Young's modulus per unit weight fraction) compared with the composites filled with pristine SWNTs or MWNTs. The respective maxima are 9680 MPa and 320 GPa. It is thus feasible for f‐SWNTs to prepare the moderately enhanced but lightweight phenolic composites. Furthermore, the incorporation of f‐SWNTs does not limit the application of phenolic resin as insulation material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6135–6144, 2009     

Grafting of montmorillonite nano‐clay with butyl acrylate and methyl methacrylate by atom transfer radical polymerization: Blends with poly(BuA‐co‐MMA)

11‐(2‐Bromo‐2‐methyl)propionyl‐oxy‐undecyl trichlorosilane atom transfer radical polymerization (ATRP) initiator was covalently attached on montmorillonite clay platelets via silylation reactions. The initiator clay was used to polymerize butyl acrylate (BuA) and methyl methacrylate (MMA) on the clay surface. Polymerization was performed in bulk monomer solution or in DMSO. Polymer modified clay was mixed with a poly(BuA‐co‐MMA) matrix. Small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) showed that clay modified in DMSO gave exfoliated composites when mixed with the matrix copolymer. Mechanical properties of the composites were studied by dynamic mechanical thermal analysis (DMTA). The results showed that the mechanical properties were improved as a function of clay content, as well with an increasing homogeneity of the nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3086–3097, 2009     

Synthesis and characterization of conducting polythiophene/carbon nanotubes composites

Conducting polythiophene (PTh)/single‐wall carbon nanotubes (SWNTs) composites were synthesized by the in situ chemical oxidative polymerization method. The resulting cablelike morphology of the composite (SWNT–PTh) structures was characterized with elemental analysis, X‐ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared, ultraviolet–visible spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, X‐ray diffraction, and transmission electron microscopy. The standard four‐point‐probe method was used to measure the conductivity of the samples. Field emission scanning electron microscopy and transmission electron microscopy analysis revealed that the SWNT–PTh composites were core (SWNTs) and shell (PTh) hybrid structures. Spectroscopic analysis data for the composites were almost identical to those for PTh, supporting the idea that SWNTs served as templates in the formation of a coaxial nanostructure for the composites. The physical properties of the composites were measured and also showed that the SWNTs were modified by conducting PTh with an enhancement of various properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5283–5290, 2006     

Preparation and characterization of covalently bonded PVA/Laponite/HAPI nanocomposite multilayer freestanding films by layer‐by‐layer assembly

The layer‐by‐layer (LBL) assembly technique is an attractive method to make functional multilayer thin films and has been applied to fabricate a wide range of materials. LBL materials could improve optical transmittance and mechanical properties if the film components were covalently bonded. Covalently bonded nanocomposite multilayer films were prepared by employing hydrophilic aliphatic polyisocyanate (HAPI) as the reactive component, to react with Laponite and polyvinyl alcohol (PVA). FT‐IR spectra suggested that HAPI reacted with Laponite and PVA at ambient temperature rapidly. Ellipsometry measurement showed that the film thickness was in linear growth. The influences of HAPI on the optical, mechanical and thermal properties of the films were investigated by UV‐Vis spectroscopy, tensile stress measurement, DSC and TGA. The obtained results showed that the optical transmittance and mechanical strength were enhanced when the film components were covalently bonded by HAPI. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 545–551     

Designing semiencapsulation based covalently self‐healable poly(methyl methacrylate) composites by Atom Transfer Radical Polymerization

Self‐healable poly(methyl methacrylate) (PMMA) composites were fabricated with embedded glycidyl methacrylate (GMA) encapsulated poly(melamine‐formaldehyde) microcapsules. The matrix polymers were synthesized via Atom Transfer Radical Polymerization using two different initiators; one linear and another hexafunctional. As the so prepared polymer matrix retains living characteristics, it can initiate a healing reaction when the encapsulated monomer reaches the matrix due to formation or extension of a crack and thus healing the system covalently. The effect of number of initiating functionality on healing characteristic was studied using both linear and 6‐armed star PMMA having same targeted molecular weight. Both the systems were able to restore 100% original fracture toughness after healing. However, the polymer matrix prepared by hexafunctional initiator restored the fracture toughness much faster than that of the linear polymer matrix. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1842–1851     

Preparation of single‐walled carbon nanotubes‐induced poly(p‐oxybenzoyl) crystals

Crystallization of oligomers was applied for the preparation of single‐walled carbon nanotubes (SWNTs)/poly(p‐oxybenzoyl) (POB) crystals using SWNTs as a nucleating agent. Polymerization conditions were investigated to induce the crystallization of POB oligomers through SWNTs. SWNTs/POB plate‐like or lozenge‐shaped crystals were successfully prepared by direct polymerization of p‐hydroxybenzoic acid (HBA) in a mixed solvent of DMF/Py with TsCl in the presence of functionalized SWNTs. The size of the plate‐like crystals were ～200 nm to 3 μm. The crystals consisted of some layers, ～3 nm thick plates. Model reactions showed that esterification reactions proceed between functionalized SWNTs and HBA monomers in the polymerization system. The obtained crystals exhibited unique morphology and high crystallinity, producing a novel SWNT/POB hybrid. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1265–1277, 2008     

Effect of treatment on the thermal conductivity and thermal diffusivity of oil‐palm‐fiber‐reinforced phenolformaldehyde composites

The thermal conductivity and thermal diffusivity of oil‐palm‐fiber‐reinforced untreated (Sample 1) and differently treated composites were measured with the transient plane source technique at room temperature and under normal pressure. All the composites were 40% oil‐palm fiber by weight. The fibers were treated with alkali (Composite 2), silane (Composite 3), and acetic acid (Composite 4) and reinforced in a phenolformaldehyde matrix. The thermal conductivity and thermal diffusivity of the composites increased after treatment to different extents. The thermal conductivity of the treated fibers as well as of the untreated fibers was calculated theoretically. The model results show that the thermal conductivity of the untreated fiber was smaller than the thermal conductivity of the treated fibers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 916–921, 2000     

Functionalized graphene sheet—Poly(vinylidene fluoride) conductive nanocomposites

PVDF nanocomposites based on functionalized graphene sheets, FGS prepared from graphite oxide, and exfoliated graphite, EG, were prepared by solution processing and compression molding. FGS remains well dispersed in the PVDF composites as evidenced by the lack of the characteristic graphite reflection in the composites. Although the α‐phase of PVDF is seen in the EG‐based composites, a mixture of α‐ and β‐phases is present in the FGS analogs. SEM and TEM imaging show smooth fractured surfaces with oriented platelets of graphite stacks and obvious debonding from the matrix in the EG‐PVDF composites. In contrast, the FGS‐PVDF composites show a wrinkled topography of relatively thin graphene sheets bonded well to the matrix. Storage modulus of the composites was increased with FGS and EG concentration. A lower percolation threshold (2 wt %) was obtained for FGS‐PVDF composites compared to EG‐PVDF composites (above 5 wt %). Lastly, the FGS‐PVDF composites show an unusual resistance/temperature behavior. The resistance decreases with temperature, indicating an NTC behavior, whereas EG‐PVDF composites show a PTC behavior (e.g., the resistance increases with temperature). We attribute the NTC behavior of the FGS based composites to the higher aspect ratio of FGS which leads to contact resistance predominating over tunneling resistance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 888–897, 2009     

Improving dispersion and integration of single‐walled carbon nanotubes in epoxy composites by using a reactive noncovalent dispersant

Uniform dispersion and strong interfacial interaction are two critical prerequisites for application of single‐walled carbon nanotubes (SWNTs) in polymer composites. To endow the composites with multifunctional feature, no damage on the chemical/electronic structure of SWNTs is also usually required. With these ends in view, two epoxide‐containing pyrene derivatives (EpPys) were designed, synthesized, and used as reactive noncovalent dispersants for developing multifunctional epoxy/SWNT composites. One having longer chain length between epoxide group and pyrene moiety, that is, EpPy‐16, shows higher dispersing efficiency and provides the nanotube dispersion with better stability, thus picking up for subsequent studies. Systematic characterization on SWNT/EpPy‐16 hybrid demonstrates that 13.2 wt % of EpPy‐16 is adsorbed on the SWNT surface through strong π‐stacking interaction, and intrinsic electronic structure of SWNTs is basically reserved. The solution‐based process adopted here preserves the good SWNT dispersing state in dispersion into the composites. Simultaneously, enhanced interfacial interaction is also realized by using EpPy‐16, which interacts noncovalently with SWNT but connects covalently to epoxy network. As a result, the composites acquire 37 and 22% increments in tensile strength and Young's modulus, respectively, relative to that of neat resin. A low‐electrical percolation threshold of 0.1 wt % SWNTs and improved thermal properties were also observed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Aligned single‐wall carbon nanotube polymer composites using an electric field

While high shear alignment has been shown to improve the mechanical properties of single‐wall carbon nanotube (SWNT)‐polymer composites, this method does not allow for control over the electrical and dielectric properties of the composite and often results in degradation of these properties. Here, we report a novel method to actively align SWNTs in a polymer matrix, which permits control over the degree of alignment of the SWNTs without the side effects of shear alignment. In this process, SWNTs were aligned via AC field‐induced dipolar interactions among the nanotubes in a liquid matrix followed by immobilization by photopolymerization under continued application of the electric field. Alignment of SWNTs was controlled as a function of magnitude, frequency, and application time of the applied electric field. The degree of SWNT alignment was assessed using optical microscopy and polarized Raman spectroscopy, and the morphology of the aligned nanocomposites was investigated by high‐resolution scanning electron microscopy. The structure of the field induced aligned SWNTs was intrinsically different from that of shear aligned SWNTs. In the present work, SWNTs are not only aligned along the field, but also migrate laterally to form thick, aligned SWNT percolative columns between the electrodes. The actively aligned SWNTs amplify the electrical and dielectric properties of the composite. All of these properties of the aligned nanocomposites exhibited anisotropic characteristics, which were controllable by tuning the applied field parameters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1751–1762, 2006     

Photoinitiators with functional groups. VI. Chemically bound sensitizers

Several benzophenone‐ and thioxanthone‐based photosensitizers (PSs) were covalently bonded to hydroxyalkylphenone‐ and aminoalkylphenone‐based photoinitiators (PIs) to enhance the rate of the excitation‐transfer effect due to the close vicinity of the PS to the PI. The properties of these new systems were investigated with UV spectroscopy and photo‐differential scanning calorimetry. Broadband irradiation experiments and selective excitation of the PS were carried out for the physical mixtures and covalently bonded PI/PS combinations to investigate the effect of excitation transfer. Selective excitation of the PS chromophore revealed that the energy transfer was significantly increased in covalently bonded initiators in comparison with the physical mixtures. This effect was most pronounced for the hydroxyalkylphenones that were sensitized by suitable benzophenone derivatives, especially at low PI concentrations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2285–2301, 2004     

Shapeable matrix‐free Spectra® fiber‐reinforced polymeric composites via high‐temperature high‐pressure sintering: Process‐structure‐property relationship

In an exploratory effort to find a new way to make high‐performance composites used in ballistic protective applications, matrix‐free Spectra® fiber‐reinforced polymeric composites are produced via a novel processing method called high‐temperature high‐pressure sintering. Mechanical testing at ambient and elevated temperatures proves that the fibers can maintain their properties after processing. The characteristics and properties of the final products vary with different processing conditions. Their microstructure and morphology were investigated using SEM and WAXD. Their mechanical properties, including interlayer adhesion, rigidity, and ballistic performance, were measured and compared with those of the conventional composites. The sintering mechanism is proposed and verified. Spectra cloth is capable of being shaped to produce complex double curvatures by a thermoforming process, using a simple hemispherical mold. Success in different molding sequences and procedures shows the versatility in manufacturing. The theoretical background for the thermoformability is explained in terms of molecular interaction, microstructure, and morphology. Selective thermomechanical properties of the molded structures were measured. By combining the knowledge and information from the aforementioned studies, the process‐structure‐property relationship is established, which gives in‐depth and better understanding of this unique high‐temperature high‐pressure sintering process for consolidating Spectra cloth. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2767–2789, 2005     

Iridium complex grafted to 3,6‐carbazole‐alt‐tetraphenylsilane copolymers for blue electrophosphorescence

We designed a 3,6‐dibromo‐9‐hexyl‐9H‐carbazole derivative with the blue emissive iridium complex bis[2‐(4,6‐difluorophenyl)pyridyl‐N,C^2′](picolinato)iridium(III) (FIrpic) linked at the alkyl terminal. Based on this monomer, novel 3,6‐carbazole‐alt‐tetraphenylsilane copolymers grafted with FIrpic were synthesized by palladium‐catalyzed Suzuki coupling reaction, and the content of FIrpic in the polymers could be controlled by feed ratio of the monomers. The polymer films mainly show blue emission from FIrpic, and the emission intensity from the polymer backbones is much weaker compared with the doped analogues, which demonstrates an efficient energy transfer from polymeric host to covalently bonded guest. The phase separation in the polymers was suppressed, which can be identified by atomic force microscopy and designed electroluminescent (EL) devices. EL devices based on the polymers exhibited blue phosphorescence from FIrpic. The luminous efficiency of preliminary devices reached 2.3 cd/A, and the efficiency roll‐off at high current densities was suppressed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1859–1865, 2010     

Coagulation method for preparing single-walled carbon nanotube/poly(methyl methacrylate) composites and their modulus,electrical conductivity,and thermal stability

A coagulation method providing a better dispersion of single-walled carbon nanotubes (SWNTs) in a polymer matrix was used to produce SWNT/poly(methyl methacrylate) (PMMA) composites. Optical microscopy and scanning electron microscopy showed an improved dispersion of SWNTs in the PMMA matrix, a key factor in composite performance. Aligned and unaligned composites were made with purified SWNTs with different SWNT loadings (0.1–7 wt %). Comprehensive testing showed improved elastic modulus, electrical conductivity, and thermal stability with the addition of SWNTs. The electrical conductivity of a 2 wt % SWNT composite decreased significantly (>10⁵) when the SWNTs were aligned, and this result was examined in terms of percolation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3333–3338, 2003     

A comparative study of temperature dependence of induction time and oscillatory frequency in polymer‐immobilized and free catalyst Belousov‐Zhabotinsky reactions

Environment‐sensitive poly(N‐isopropylacrylamide) (PNIPAM) microgel particles with covalently bonded ruthenium(4‐vinyl‐4′‐methyl‐2,2′‐bipyridine) bis (2,2′‐bipyridine) [Ru(vmbipy)(bipy)₂] display periodic size changes when placed in Belousov‐Zhabotinsky (BZ) reaction substrates. The temperature dependency of the induction time and oscillatory frequency of the BZ reaction in this polymer‐immobilized catalyst system were compared to the bulk BZ reaction with the catalyst in the solution phase. Prolonged induction times are observed for the immobilized catalyst, compared with free catalyst, while little difference is observed on the oscillation frequency. The Arrhenius frequency factor calculated using the induction time for the immobilized catalyst BZ reaction is about seven times smaller than that for the free catalyst Ru(bipy) case. On the other hand, the Arrhenius frequency factors calculated using the oscillatory frequency are almost the same, showing similar reaction kinetics during the BZ oscillations. The tunability of the induction time using a polymer matrix, as we observed here, while maintaining similar oscillatory behavior, should provide a new dimension to control the self‐assembling of BZ active particles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 847–854, 2009     

Anisotropic mechanical properties of thermoplastic elastomers in situ reinforced with thermotropic liquid‐crystalline polymer fibers revealed by biaxial deformations

The anisotropic mechanical properties of the thermoplastic elastomer (TPE) in situ reinforced with thermotropic liquid‐crystalline polymer (TLCP) fibers were investigated by uniaxial, strip‐biaxial, and equibiaxial tensile measurements. The in situ composite sheets were prepared from an immiscible blend of a TLCP, Rodrun LC3000, and a TPE, styrene‐(ethylene butylene)‐styrene (SEBS) triblock copolymer, by a melt extrusion process. The uniaxial orientation of the TLCP fibers in the TPE matrix generated during processing yielded a significant mechanical anisotropy in the composites. The biaxial tensile measurements clearly demonstrated the anisotropic mechanical properties of the composites: The modulus in the direction parallel to the machine direction (MD) was considerably higher than that in the transverse direction (TD), even at large deformations; in equibiaxial stretching, the yield strain in the MD was smaller than that in the TD; the composite containing 10 wt % of TLCP exhibited the highest mechanical anisotropy among the composites, with 0–30 wt % TLCP. The latter result was in accord with the SEM observation that the composite with 10 wt % of TLCP possessed the best fibrillar morphology and the highest degree of uniaxial orientation of the TLCP fibers. The yield strains in uni‐ and biaxial elongation for the composite containing 10 wt % of TLCP were almost the same as those for the neat styrene‐ethylene butylene‐styrene. The TLCP phase with good fibrillation did not appreciably alter the original yielding characteristics of the elastomer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 135–144, 2005     

Spectroscopic investigations on polypropylene‐carbon nanofiber composites. I. Raman and electron spin resonance spectroscopy

Isotactic polypropylene‐vapor grown carbon nanofiber composites containing various fractions of carbon nanofibers, ranging from 0 to 20 wt %, have been prepared. Raman spectroscopy was used to analyze the effect of the dispersion of carbon nanofibers within polypropylene and the interactions between carbon nanofibers and macromolecular chains. The as‐recorded Raman spectra have been successfully fitted by a linear convolution of Lorentzian lines. Changes of the Raman lines parameters (position, intensity, width, and area) of polypropylene and carbon nanofibers were analyzed in detail. The Raman spectra of the polymeric matrix—at low concentrations of nanofibers—show important modifications that indicate strong interactions between carbon nanofibers and the polymeric matrix reflecting by vibrational dephasing of macromolecular chains. The Raman spectrum of carbon nanofibers is sensitive to the loading with carbon nanofibers, showing changes of the resonance frequencies, amplitudes, and width for both D‐ and G‐bands. Raman data reveals the increase of the disorder, as the concentration of carbon nanofibers is increased. The presence of the typical ESR line assigned to conducting electrons delocalized over carbon nanofibers is confirmed and the presence of a spurious magnetic line due to catalyst's residues is reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1644–1652, 2009     

A novel polymeric stabilizing system for modified lyocell solutions

A novel polymeric stabilizer consisting of iminodiacetic acid sodium salt (ISDB) and benzyl amine (BSDB) covalently bound to a styrene/divinyl benzene copolymer were studied. Calorimetric, spectroscopic, rheological, and high performance liquid chromatography analysis revealed distinctive improvements of the thermal stability of modified Lyocell solutions compared to the unstabilized solution and to that with conventional NaOH/propyl gallate stabilizer. Segregation processes of the system cellulose/N‐methylmorpholine‐N‐oxide and autocatalytic reactions caused by carboxyl group‐containing additives are suppressed by ISDB/BSDB. Concerning to surface‐active additives, enhanced thermal stability is only received for a weakly reactive charcoal. In the case of nanoscaled carbon black modifier, autocatalytic reactions indicated by isoperibolic measures are prevented by the new polymeric stabilizer system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1702–1713, 2006     

Facile and quick synthesis of poly(N‐methylolacrylamide)/polyhedral oligomeric silsesquioxane graft copolymer hybrids via frontal polymerization

We report on a new strategy for fabricating well‐defined POSS‐based polymeric materials with and without solvent by frontal polymerization (FP) at ambient pressure. First, we functionalize polyhedral oligomeric silsesquioxane (POSS) with isophorone diisocyanate (IPDI). With these functionalized POSS‐containing isocyanate groups, POSS can be easily incorporated into a poly(N‐methylolacrylamide) (PNMA) matrix via FP in situ. Constant velocity FP is observed without significant bulk polymerization. The morphology and thermal properties of POSS‐based hybrid polymers prepared via FP are comparatively investigated on the basis of scanning electronic microscopy (SEM) and thermogravimetric analysis (TGA). Results show that the as‐prepared POSS‐based polymeric materials exhibit a higher glass transition temperature than that of pure PNMA, ascribing to modified POSS well‐dispersed in these hybrid polymers. Also, the products with different microstructures display different thermal properties. The pure PNMA exhibits a featureless morphology, whereas a hierarchical morphology is obtained for the POSS‐based polymeric materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1136–1147, 2009     

The effect of length of single‐walled carbon nanotubes (SWNTs) on electrical properties of conducting polymer–SWNT composites

DC conductivity of conjugated polymer‐single‐walled carbon nanotube (SWNT) composite films has been measured for different SWNT concentrations. The composite was prepared by dispersing SWNTs in the poly (3‐octylthiophene), P3OT matrix already dissolved in xylene. The conductivity of the composite films showed a rapid increase as the SWNT concentration increases beyond a certain value. This behavior is explained in terms of percolating paths provided by the SWNTs in the volume of polymer matrix. To investigate the effect of length of nanotubes on the percolation conductivity, different SWNT samples were employed with similar diameter but varying tube lengths. It was found that the conductivity of the composite films is strongly dominated by the length of the nanotubes. Lower percolation limit and high conductivity value of composite films is observed for longer nanotubes. Furthermore, the conductivity is observed to be dependent on the size of the host polymer molecule also. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 89–95, 2010