Preparation and characterization of epoxy/polyhedral oligomeric silsesquioxane hybrid nanocomposites

We have prepared epoxy/polyhedral oligomeric silsesquioxane (POSS) nanocomposites by photopolymerization from octakis(glycidylsiloxy)octasilsesquioxane (OG) and diglycidyl ether of bisphenol A. We used nuclear magnetic resonance, Raman, and Fourier transform infrared spectroscopies to characterize the chemical structure of the synthetic OG. Differential scanning calorimetry and dynamic mechanical analysis (DMA) revealed that the nanocomposites possessed higher glass transition temperatures than that of the pristine epoxy resin. Furthermore, DMA indicated that all of the nanocomposites exhibited enhanced storage moduli in the rubbery state, a phenomenon that we ascribe to both the nano‐reinforcement effect of the POSS cages and the additional degree of crosslinking that resulted from the reactions between the epoxy and OG units. Thermogravimetric analysis revealed that the thermal stability of the nanocomposites was better than that of the pristine epoxy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1927–1934, 2009     

Preparation and properties of conductive silver/photosensitive polyimide nanocomposites

A new electrically conductive photoresist has been developed. It is based on the dispersion of silver nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 2‐Mercaptopropionic acid was used as the surfactant to modify the silver nanoflake surface for the dispersion of silver nanoflakes in the polymer. The silver/PSPI nanocomposites showed electrical conductivity at a low silver content of 10 wt %. The electrical conductivity of the silver/PSPI nanocomposites ranged from 10 to 10⁴ S/cm, which was dependent on the silver weight fraction in the resist formulation. Patterns with a resolution of 30 μm were obtained from the silver/PSPI nanocomposites. The silver/PSPI nanocomposites had excellent thermal properties. Their glass transition temperatures were above 360 °C and thermal decomposition temperatures were over 420 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1575–1583, 2009     

Poly(cyclohexene oxide)/clay nanocomposites by photoinitiated cationic polymerization via activated monomer mechanism

Poly(cyclohexene oxide) (PCHO)/clay nanocomposites were prepared by in situ photoinitiated activated monomer cationic polymerization. The polymerization of cyclohexene oxide through the interlayer galleries of the clay can provide distribution of the clay layers in the polymer matrix homogenously and results in the formation of PCHO/clay nanocomposites. The exfoliated structures were characterized by X‐ray diffraction spectroscopy, thermogravimetric analysis, transmission electron microscopy, and atomic force microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5328–5335, 2009     

Thermal degradation and kinetic analysis of biodegradable PBS/multiwalled carbon nanotube nanocomposites

In this study, carbon nanotubes (CNTs) were first modified using N,N′‐ dicyclohexylcarbodiimide (DCC) dehydrating agents. Subsequently, the poly(butylene succinate)/multiwalled carbon nanotube (PBS/MWNTs) nanocomposites were prepared through facile melt blending. Thermal degradation of these PBS/MWNT nanocomposites was investigated; the kinetic parameters of degradation were calculated using the Coats and Redfern, Ozawa, and Horowitz and Metzger methods, respectively. It was found that the degradation reaction mechanism of PBS and the CNT‐C18 containing nanocomposites at lower temperature was likely to produce an F1 model through reaction of random chain cleavage (cis‐elimination). However, the reaction mechanism at higher temperature was likely to be a D1 model because of the dominant diffusion control effect. Moreover, it was found that the activation energies of CNT‐C18‐containing PBS nanocomposites were first increased with the content of CNT‐C18, but then decreased after the content was larger than 0.5 wt % for all models at differing heating rates. This may be due to the formation of a conductive network of CNTs in the polymer matrix at higher content of CNTs, which lead to better heat and electrical conductivity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1231–1239, 2009     

Nonisothermal melt crystallization and subsequent melting behavior of biodegradable poly(hydroxybutyrate)/multiwalled carbon nanotubes nanocomposites

In this work, nonisothermal melt crystallization and subsequent melting behavior of poly(hydroxybutyrate) (PHB) and its nanocomposites at different multiwalled carbon nanotubes (MWCNTs) loadings were investigated. Increasing the MWCNTs loadings has enhanced the nonisothermal melt crystallization of PHB significantly in the nanocomposites when compared with that of the neat PHB; furthermore, increasing the cooling rates shift the crystallization exotherms to low temperature range for both neat PHB and its nanocomposites. Double melting behavior is found for both neat PHB and its nanocomposites crystallized nonisothermally from the melt, which is explained by the melting, recrystallization, and remelting model. Effects of the MWCNTs loadings, cooling rates, and heating rates on the subsequent melting behavior of PHB were studied in detail. It is found that increasing the MWCNTs loadings, decreasing the cooling rates, and increasing the heating rates would restrict the occurrence of the recrystallization of PHB in the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2238–2246, 2009     

Clay dispersibility and mechanical property of the epoxy/clay nanocomposites prepared by different treatment methods

The bisphenol‐A type epoxy resin was combined with layered clays. Three types of epoxy/clay nanocomposites were prepared by different clay pretreatment methods, that is, the slurry (clay swelling with polar solvent), organo, and solubilization (organoclay swelling with polar solvent) methods. The organo and solubilization systems showed good dispersibility. The basal spacing of the layered clays in the obtained nanocomposites was evaluated by XRD and TEM observations. The basal spacing of the nanoclay in the solubilization system drastically increased. The mechanical properties were improved with the increase in the clay dispersion. A high modulus and fracture toughness were obtained by improvement of the clay dispersion into the matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1753–1761, 2009     

Hybrid miniemulsion polymerization of acrylic/alkyd systems and characterization of the resulting polymers

The hybrid miniemulsion polymerization of acrylates in the presence of alkyd resin was carried out. The polymers obtained were characterized via gel permeation chromatography, carbon nuclear magnetic resonance, and differential scanning calorimetry analysis and selective extraction; they had a quite broad molecular weight distribution. The double bonds that served as grafting sites of the alkyd onto the polyacrylate were mostly those near acid groups. The final product contained some free alkyd and some free polyacrylate, but the predominant form was poly(acrylate-graft-alkyd). This confirmed that monomer droplet nucleation is the predominant nucleation mechanism for this hybrid miniemulsion polymerization system. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4159–4168, 1999     

Atypical transition temperature dependence of poly(N‐isopropylacrylamide) and poly(N‐isopropylacrylamide‐co‐acrylamide) nanocomposites on the content of exfoliated montmorillonites

Exfoliated montmorillonite (MMT)/poly(N‐isopropylacrylamide) (PNIPAAm) and MMT/poly(N‐isopropylacrylamide‐co‐acrylamide) [P(NIPAAm‐co‐AAm)] nanocomposites were fabricated by soap‐free emulsion polymerization. Interestingly, as the content of MMT was increased from 0 to 10 wt %, the glass transition temperature of MMT/PNIPAAm was decreased from 145 to 122 °C, whereas that of the MMT/P(NIPAAm‐co‐AAm) increased from 95 to 153 °C. Although the lower critical solution temperature (LCST) of 32 °C for the MMT/PNIPAAm nanocomposites in aqueous solutions was slightly increased with the content of MMT, that of the MMT/P(NIPAAm‐co‐AAm) was decreased from 70 to 65 °C. A mechanism that the hydrogen bonds between the amide groups of PNIPAAm were interfered by the exfoliated MMT nano‐platelets for the MMT/PNIPAAm nanocomposites and the preferred absorption of acrylamide units to the MMT nanoplatelets rather than N‐isopropylacrylamide in the MMT/P(NIPAAm‐co‐AAm) nanocomposites was suggested to interpret these unusual transition behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 524–530, 2009     

Noncovalent functionalization of multiwalled and double‐walled carbon nanotubes: Positive effect of the filler functionalization on high glass transition temperature epoxy resins

Double‐walled carbon nanotubes (DWCNTs) and multiwalled carbon nanotubes (MWCNTs) were modified using melamine to attach ? NH₂ to the surface of these fillers, without previous oxidation of their graphene layers. FT‐Raman, elemental (chemical) and thermogravimetric analysis, confirmed the modification, which was more extensive for DWCNTs. The potential of this modification was evaluated by adding the melamin‐modified nanotubes to thermosets based on diglycidyl ether of bisphenol A (resin) and polycyclic amine (hardener). Broadening of the glass transition interval and an increase between 7 and 8 °C of the glass transition temperatures show better filler/matrix interaction for the nanocomposites based on melamine‐modified nanotubes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1860–1868, 2009     

Polyethylene/graphite nanocomposites obtained by in situ polymerization

The synthesis of polyethylene/graphite nanocomposites by in situ polymerization was achieved using the catalytic system Cp₂ZrCl₂ (bis(cyclopentadienyl)zirconium(IV) dichloride)/methylaluminoxane (MAO). Graphite with nano dimensions, previously treated with MAO, was added into the reactor as filler at percentages of 1, 2, and 5% (w/w). XRD analysis showed that the chemical and thermal treatments employed preserve the structure of the graphite sheets. The formation of graphite nanosheets and nanocomposites was confirmed by TEM and AFM. TEM micrographics showed that the polyethylene grew between the graphene nanosheets, giving intercalated and exfoliated graphite nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 692–698, 2010     

Effect of different matrices and nanofillers on the rheological behavior of polymer‐clay nanocomposites

In this work, a comprehensive study of the rheological behavior under shear and isothermal and nonisothermal elongational flow of low density polyethylene (LDPE) and ethylene‐vinyl acetate copolymer (EVA) based nanocomposites was reported to evaluate their “filmability”, that is, the ability of these material to be processed for film forming applications. The influence of two different kinds of organoclay – namely Cloisite 15A and Cloisite 30B – and their concentration was evaluated. The presence of filler clearly affects the rheological behavior in oscillatory state of polyolefin‐based nanocomposites but the increase of complex viscosity and the shear thinning are not dramatic. A larger strain‐hardening effect in isothermal elongational flow is shown by the nanocomposites compared to that of the pure matrix, particularly for EVA based nanocomposites. The melt strength measured under nonisothermal elongational flow increases in the presence of the nanofiller, while the drawability is only slightly lower than that measured for the neat matrix. Moreover, the rheological behavior under nonisothermal elongational flow of EVA‐based nanocomposites is similar for both nanoclays used. Differently, LDPE‐based nanocomposites show a strong dependence on the type of organoclay. Finally, the mechanical properties of the materials were measured by tensile tests. They revealed that the presence of the filler provokes, in all the cases, an increase of the rigidity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 344–355, 2010     

Properties of covalently bonded layered‐silicate/polystyrene nanocomposites synthesized via atom transfer radical polymerization

Covalently bonded layered silicated/polystyrene nanocomposites were synthesized via atom transfer radical polymerization in the presence of initiator‐modified layered silicate. The resulting nanocomposites had an intercalated and partially exfoliated structure, as confirmed by X‐ray diffraction and transmission electron microscopy. The thermal properties of the nanocomposites improved substantially over those of neat polystyrene. In particular, a maximum increase of 35.5 °C in the degradation temperature was displayed by these nanocomposites. Additionally, the surface elastic modulus and hardness of these nanocomposites were more than double those of pure polystyrene. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 534–542, 2005     

Nanostructural modifications of polyamide/MMT hybrids under isothermal and nonisothermal elongational flow

The aim of this work is to investigate the effects of elongational flow on the nanoscale arrangement of the silicate inside polyamide‐based nanocomposites. Hybrids, at different loadings of a commercial organoclay, were produced by melt compounding using two polyamide matrices, a nylon‐6, and a copolyamide with similar molecular weight and rheological properties. The elongational flow characterization was performed under both isothermal and nonisothermal conditions by using, respectively, an elongational rheometer (SER) and a fiber‐spinning technique. The extensional rheological response of melt‐compounded nanocomposites, correlated to TEM and X‐ray analyses, was used to probe the nanostructural modifications developed during the uniaxial stretching. The results demonstrated that isothermal and nonisothermal elongational flow can modify the nanomorphology of the nanocomposite hybrids affecting the degree of silicate exfoliation as well as the extent of silicate orientation upon the stretching direction. The entity of structural modifications induced by the stretching were highly dependent on the initial nanomorphological state and on the polymer‐clay affinity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 981–993, 2009     

Patterned immobilization of biomolecules by using ion irradiation‐induced graft polymerization

A new method for biomolecular patterning based on ion irradiation‐induced graft polymerization was demonstrated in this study. Ion irradiation on a polymer surface resulted in the formation of active species, which was further used for surface‐initiated graft polymerization of acrylic acid. The results of the grafting study revealed that the surface graft polymerization using 20 vol % of acrylic acid on the poly(tetrafluoroethylene) (PTFE) film irradiated at the fluence of 1 × 10¹⁵ ions/cm² for 12 h was the optimum graft polymerization condition to achieve the maximum grafting degree. The results of the fluorescence microscopy also revealed that the optimum fluence to achieve the maximum fluorescence intensity was 1 × 10¹⁵ ions/cm². The grafting of acrylic acid on the PTFE surfaces was confirmed by a fluorescence labeling method. The grafted PTFE films were used for the immobilization of amine‐functionalized p‐DNA, followed by hybridization with fluorescently tagged c‐DNA. Biotin‐amine was also immobilized on the acrylic acid grafted PTFE surfaces. Successful biotin‐specific binding of streptavidin further confirmed the potential of this strategy for patterning of various biomolecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6124–6134, 2009     

New poly(butylene succinate)/layered silicate nanocomposites. II. Effect of organically modified layered silicates on structure,properties, melt rheology,and biodegradability

A series of new poly(butylene succinate) (PBS)/layered silicate nanocomposites were prepared successfully by simple melt extrusion of PBS and organically modified layered silicates (OMLS). Three different types of OMLS were used for the preparation of nanocomposites: two functionalized ammonium salts modified montmorillonite and a phosphonium salt modified saponite. The structure of the nanocomposites in the nanometer scale was characterized with wide-angle X-ray diffraction and transmission electron microscopic observations. With three different types of layered silicates modified with three different types of surfactants, the effect of OMLS in nanocomposites was investigated by focusing on four major aspects: structural analysis, materials properties, melt rheological behavior, and biodegradability. Interestingly, all these nanocomposites exhibited concurrent improvements of material properties when compared with pure PBS. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3160–3172, 2003     

Low molecular weight aromatic compounds possessing a nonflammable characteristic in fluoroalkyl end‐capped acrylic acid oligomer/silica nanocomposite matrices after calcination at 800 °C under atmospheric conditions

Fluoroalkyl end‐capped acrylic acid oligomer [R_F‐(ACA)_n‐R_F] reacted with tetraethoxysilane and silica nanoparticles in the presence of low molecular weight aromatic compounds [ Ar‐H ] such as cetylpyridinium chloride (CPC) and bisphenol AF under alkaline conditions to afford R_F‐(ACA)_n‐R_F/SiO₂ nanocomposites‐encapsulated Ar‐H in 47–94% isolated yields. These fluorinated silica nanocomposites‐encapsulated Ar‐H can exhibit no weight loss behavior corresponding to the contents of Ar‐H after calcination at 800 °C under atmospheric conditions, although fluoroalkyl end‐capped acrylic acid oligomer in the nanocomposites decomposed completely under similar conditions. UV‐vis spectra of well‐dispersed methanol solutions of R_F‐(ACA)_n‐R_F/SiO₂/CPC nanocomposites before calcination show that CPC can be encapsulated into fluorinated silica nanocomposites with encapsulated ratios: 23–43%. The fluorinated nanocomposites after calcination was found to exhibit a higher antibacterial activity related to the presence of CPC in the composites. Encapsulated bisphenol AF into R_F‐(ACA)_n‐R_F/SiO₂ nanocomposites before and after calcination at 800 °C can exhibit a good releasing ability toward methanol with released ratios: 48 and 26%, respectively. ¹H MAS NMR, HPLC analysis, and LC‐MS spectra of R_F‐(ACA)_n‐R_F/silica nanocomposites‐encapsulated bisphenol AF also showed the presence of bisphenol AF in the nanocomposites even after calcination at 800 °C under atmospheric conditions. These findings suggest that CPC and bisphenol AF can exhibit a nonflammable characteristic in the fluorinated silica nanocomposites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Isothermal crystallization behavior of exfoliated‐PP/IMMT nanocomposites via in situ polymerization

Highly exfoliated isotactic‐polypropylene/alkyl‐imidazolium modified montmorillonite (PP/IMMT) nanocomposites have been prepared via in situ intercalative polymerization. TEM and XRD results indicated that the obtained composites were highly exfoliated PP/IMMT nanocomposites and the average thickness of IMMT in PP matrix was less than 10 nm, and the distance between adjacent IMMT particles was in the range of 20–200 nm. The isothermal crystallization kinetics of highly exfoliated PP/IMMT nanocomposites were investigated by using differential scanning calorimeter(DSC) and polarized optical microscope (POM). The crystallization half‐time t_1/2, crystallization peak time t_max, and the Avrami crystallization rate constant K_n showed that the nanosilicate layers accelerate the overall crystallization rate greatly due to the nucleation effect, and the crystallization rate was increased with the increase in MMT content. Meanwhile, the crystallinity of PP in nanocomposites decreased with the increase in clay content which indicated the PP chains were confined by the nanosilicate layers during the crystallization process. Although the well‐dispersed silicate layers did not have much influence on spherulites growth rate, the nucleation rate and the nuclei density increased significantly. Accordingly, the spherulite size decreased with the increase in MMT content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2215–2225, 2009     

Synthesis and characterization of novel PDMS nanocomposites using POSS derivatives as cross‐linking filler

We report the synthesis and characterization of novel elastomeric nanocomposites containing polyhedral oligomeric silsesquioxanes (POSS) as both the cross‐linker and filler within a polydimethylsiloxane (PDMS) polymer matrix. These polymer composites were prepared through the reaction of octasilane‐POSS (OS‐POSS) with vinyl‐terminated PDMS chains using hydrosilylation chemistry. In addition, larger super‐POSS cross‐linkers, consisting of two pendant hepta(isobutyl)POSS molecules attached to a central octasilane‐POSS core, were also used in the fabrication of the PDMS composites. The chemical incorporation of these POSS cross‐linkers into the PDMS network was verified by solid‐state ¹H magic angle spinning NMR. Based on dynamic mechanical analysis, the PDMS nanocomposites prepared with the octafunctional OS‐POSS cross‐linker exhibited enhanced mechanical properties relative to polymer systems prepared with the tetrafunctional TDSS cross‐linker at equivalent loading levels. The observed improvements in mechanical properties can be attributed to the increased dimensionality of the POSS cross‐linker. The PDMS elastomers synthesized from the larger super‐POSS molecule showed improved mechanical properties relative to both the TDSS and OS‐POSS composites due to the increased volume‐fraction of POSS filler in the polymer matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2589–2596, 2009     

Orientation behavior of attapulgite nanoparticles in poly(acrylonitrile)/attapulgite solutions by rheological analysis

Nanocomposites based on poly(acrylonitrile) (PAN) and attapulgite (AT) had been prepared by solution blending in dimethyl sulfoxide (DMSO). The rheological properties of the nanocomposites solutions were investigated by HAAKE rheometer with plate‐cone geometry. The steady and oscillation shear experiments were carried out to investigate the effects of clay exfoliation and orientation as well as polymer‐clay interaction. The presence of small amount of AT nanoparticles with large aspect ratio improved the fluidity of these PAN solutions under low shear rate, whereas large amount of AT will reduce its aspect ratio by aggregation and constrain the polymer segment motion in the solutions. The relaxation and disentanglement behaviors of the PAN chains in nanocomposite solutions were also studied by oscillation and thixotropic experiments, from which, it can be concluded that well dispersed and oriented AT nanorods will reduce interaction among macromolecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 945–954, 2009     

Thiocarbonylthio end group removal from RAFT‐synthesized polymers by a radical‐induced process

The removal of thiocarbonylthio end groups by radical‐addition‐fragmentation‐ coupling from polymers synthesized by RAFT polymerization has been studied. We found that a method, which involves heating the polymer with a large excess (20 molar equivalents) of azobis(isobutyronitrile) (AIBN), while successful with methacrylic polymers, is less effective with styrenic or acrylic polymers and provides only partial end group removal. This is attributed to the propagating radicals generated from the latter polymers being poor radical leaving groups relative to the cyanoisopropyl radical. Similar use of lauroyl peroxide (LPO) completely removes the thiocarbonylthio groups from styrenic or acrylic polymers but, even with LPO in large excess, produces a polymer with a bimodal molecular weight distribution. The formation of a peak of double molecular weight is indicative of the occurrence of self‐termination and ineffective radical trapping. We now report that by use of a combination of LPO (2 molar equivalents) and AIBN (20 molar equivalents) we are able to completely remove thiocarbonylthio end groups of styrenic or acrylic polymers and minimize the occurrence of self termination. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6704–6714, 2009