Polypropylene-polyhedral oligomeric silsesquioxanes (POSS) nanocomposites

In this paper, the influence of the functionalisation of polyhedral oligomeric silsesquioxanes (POSS) cages on the preparation and properties of polypropylene (PP) based nanocomposites is studied.POSS with different chain lengths (octamethyl-, octaisobutyl- and octaisooctyl-POSS) are taken in to account and melt mixed with PP. The resulting composites are characterised as regards thermal and morphological characteristics by means of DSC, TGA, SEM and X-ray diffraction.A good dispersion is obtained particularly at low loadings of POSS functionalised with longer organic chains.Important features are recognised as regards the crystallisation behaviour of PP by octamethyl- and octaisobutyl-POSS: The former acting as a nucleating agent and the second inducing PP polymorphism.     

Synthesis and bulk organization of polymer nanocomposites based on hemi/ditelechelic poly(propylene oxide) end-functionalized with POSS cages

A model hybrid material based on a molten and flexible polymer - atactic poly(propylene oxide) (PPO) - tethered with a monofunctionalized POSS molecule incorporated at one or both chain ends was synthesized. Asymmetric PPO chains with a hydroxyl terminal group were first allylated, using a Williamson ether synthesis. Hydrosilylation of the allyl end-functionalized PPO chains with hydro-heptacyclopentyl-substituted POSS cages resulted in the anchoring of a single POSS unit per allyl functionality. Two distinct PPO-POSS nanocomposites were prepared: one with a large fraction of PPO chains having two POSS end-groups; one made of a hemi-telechelic singly substituted PPO-POSS chain. Both architectures contained a similar POSS content. The influence of the number of POSS end-groups per chain on the bulk organization was investigated by wide-angle X-ray diffraction. For each nanocomposite, part of the POSS particles crystallize but a propensity to form larger crystalline regions is observed as the fraction of di-telechelic PPO-POSS chains increases. These variations in the bulk organization of the POSS cages within the molten PPO matrix influence the thermal oxidative degradation behavior of the polymer matrix, as evidenced by thermogravimetric analysis.     

The synthesis and characterization of polystyrene/magnetic polyhedral oligomeric silsesquioxane (POSS) nanocomposites

Fc-CHCH-C₆H₆-(C₅H₉)₇Si₈O₁₂ (POSS1, Fc: ferrocene) which contain both metal and CC double bond was firstly synthesized by Wittig reaction. The chemical structure of POSS1 was characterized by FTIR, ¹H, ¹³C and ²⁹Si NMR, mass spectrometry and elemental analysis, and the magnetic property of POSS1 have also been studied. Polystyrene composites containing inorganic-organic hybrid polyhedral oligomeric silsesquioxane (POSS1) were prepared by bulk free radical polymerization. XRD and TEM studies indicate that POSS1 is completely dispersed at molecular level in PS matrix when 1 wt% POSS1 is introduced, while some POSS1-rich nanoparticals are present when content of POSS1 is beyond 3 wt%. GPC results show that molecular weight of the PS/POSS1 nanocomposites are increased with addition of POSS1. TGA and TMA data show the thermal stabilities of PS/POSS1 nanocomposites have been improved compared to neat PS. The PS/POSS1 nanocomposites also display higher glass transition temperatures (T_g) in comparison with neat PS. Viscoelastic properties of PS/POSS1 nanocomposites were investigated by DMTA. The results show the storage modulus (E′) values (temperature>T_g) and the loss factor peak values of the PS/POSS1 nanocomposites are higher than that of neat PS. Mechanical properties of the PS/POSS1 nanocomposites are improved compared to the neat PS.     

Synthesis and interfacial properties of montmorillonite/polypyrrole nanocomposites

Montmorillonite/polypyrrole (MMT/PPy) nanocomposites were prepared by the in situ polymerization of pyrrole in the presence of MMT. The morphology of the MMT/PPy nanocomposites as examined by scanning electron microscopy differs slightly from that of the untreated MMT but markedly from that of polypyrrole. X-ray photoelectron spectroscopy (XPS) showed that the materials have MMT-rich surfaces, an indication that polypyrrole is essentially intercalated in the host clay galleries. The transmission electron microscopy showed, that the interlamellar spacing of the untreated MMT increased from 1.25 to 18.9 nm, when compared to nanocomposite MMT/10.8% PPy. Moreover, XPS highlighted the cation exchange of Na⁺ from montmorillonite by K⁺ (from the oxidant) and by the positively charged polypyrrole chains. Inverse gas chromatography indicated that the nanocomposites are high surface energy materials with a dispersive contribution to the surface energy reaching 200 mJ/m² at 150 °C, for a PPy loading of 21.4 wt%. The values of the MMT/PPy nanocomposites were correlated to the changes in the specific surface area of the MMT induced by the intercalation of polypyrrole.     

Morphology evolutions of organically modified montmorillonite/polyamide 12 nanocomposites

Organically modified montmorillonites (OMMTs) by octadecylammonium chloride with two adsorption levels were dispersed in polyamide 12 (PA12) matrices with two molecular weights for different melt mixing times in order to investigate morphology evolutions and factors influencing fabrication of PA12 nanocomposites. Different adsorption levels of the modifier in the OMMTs provide different environments for diffusion of polymer chains and different attractions between MMT layers. Wide-angle X-ray diffraction (WAXD), transmission electron microscope (TEM) and gas permeability were used to characterize morphologies of the nanocomposites. Both OMMTs can be exfoliated in the PA12 matrix with higher molecular weight, but only OMMT with lower adsorption level can be exfoliated in the PA12 matrix with lower molecular weight. It was attributed to the differences in the levels of shear stress and molecular diffusion in the nanocomposites. The exfoliation of OMMT platelets results from a combination of molecular diffusion and shear. After intercalation of PA12 into interlayer of OMMT in the initial period of mixing, further dispersion of OMMTs in PA12 matrices is controlled by a slippage process of MMT layers during fabricating PA12 nanocomposites with exfoliated structure.     

Thermal transitions of montmorillonite/polyurethane nanocomposites

The hard-segment phase thermal transitions and heat-resistance of benzidine-modified-montmorillonite (BZD-Mont)/polyurethane nanocomposites of different hard segment contents were found to be affected by a small amount of BZD-Mont. In particular, the presence of less than 5 wt% layered silicates from BZD-Mont can result in hard segments not only having a more thermally stable long-range order and a higher melting temperature, but also showing a loss of crystallinity of the hard segment in polyurethane. Additionally, the degradation temperature of BZD-Mont/polyurethane nanocomposite was slightly higher than that of pure polyurethane.     

Ultrasonic oscillations induced morphology and property development of polypropylene/montmorillonite nanocomposites

Polypropylene/montmorillonite nanocomposites (PPCNs) with 3% organophilic montmorillonite (OMMT) content were prepared via ultrasonic extrusion. The objective of present study was to investigate the effects of ultrasonic oscillations in processing on the morphology and property development of PPCNs. XRD and TEM results confirmed the intercalated structure of OMMT in conventional nanocomposite (without ultrasonic treatment) and ultrasonicated nanocomposite, but ultrasonic oscillations could make silicate layers finely dispersed and a little exfoliated. According to SEM, the OMMT particles were evenly and finely dispersed in the ultrasonicated nanocomposite via ultrasonic oscillations, and the aggregation size of clay particles was about 100 nm, which is less than that in conventional nanocomposite. The crystalline dimension, crystalline morphology and the growth rate of crystallization in PPCNs were investigated by DSC and PLM, it was found that the OMMT particles and ultrasonic oscillations played an important role in the nucleation rate, crystallization temperature and spherulite size of PP matrix in nanocomposites. Compared with conventional nanocomposite, the mechanical properties of the ultrasonicated nanocomposite increased due to the improved dispersion of OMMT and diminished spherulite size. The thermal stability and the rheological behavior of PP and its nanocomposites were both studied by thermogravimetry and high pressure rheometer, respectively.     

Effect of sodium montmorillonite source on nylon 6/clay nanocomposites

The effect of sodium montmorillonite source on the morphology and properties of nylon 6 nanocomposites was examined using equivalent experimental conditions. Sodium montmorillonite samples acquired from two well-known mines, Yamagata, Japan, and Wyoming, USA, were ion exchanged with the same alkyl ammonium chloride compound. The resulting organoclays were extruded with a high molecular weight grade of nylon 6 under the same processing conditions. Quantitative analysis of TEM photomicrographs of the two nanocomposites reveal a slightly larger average particle length and a slightly higher degree of platelet exfoliation for the Yamagata based nanocomposite than the Wyoming version, thus, translating into a higher particle aspect ratio. The stress-strain behavior of the nanocomposites appears to reflect the nanocomposite morphology, in that higher stiffness and strengths are attainable with the increased particle aspect ratio. Moreover, the trends in stiffness behavior between the two types of nanocomposites may be explained by conventional composite theory.     

New fabricate of styrene-butadiene rubber/montmorillonite nanocomposites by anionic polymerization

Styrene-butadiene rubber/montmorillonite (SBR/MMT) nanocomposites were successfully synthesized by in situ living anionic polymerization with n-BuLi as initiator. The results from kinetics study and ¹H NMR indicated that the addition of organophilic montmorillonite (OMMT) did not changed the living copolymerization and the components of the copolymer on the whole when OMMT content was lower than 3 wt %. However, gel permeation chromatography showed that the introduction of OMMT resulted in small amount of high-molecular weight fraction of SBR in the composites, leading to an increase in the weight-average molecular weight and polydispersity index, but the unchangeableness of the number-average molecular weight. The result from transmission electron microscopy and X-ray diffraction revealed that a completely exfoliated structure existed in the nanocomposite with 25 wt % styrene and OMMT content from 1 to 4 wt %, and styrene played an important role in the expanding of OMMT layers. Moreover, the nanocomposites possessed higher glass-transition temperature, thermal stability, tensile strength and elongation at break than SBR when the OMMT content ranged from 2.5 to 4 wt %. A schema was proposed to illustrate the formation of the nanocomposite and the exfoliation structure with physical cross-linking between SBR chains and OMMT.     

Dielectric relaxation in montmorillonite/polymer nanocomposites

We report dielectric relaxation behavior in blends of sodium montmorillonite particles (MM) with a series of polymers (i.e., polyisoprene (PI), poly(propylene glycol) (PPG), and poly(butylene oxide) (PBO)). These polymers are known to exhibit the dielectric normal mode due to the fluctuation of the end-to-end vector as well as the segmental mode due to local, segmental fluctuations. The data indicate that all blend systems exhibit an additional relaxation process at a temperature region below the glass transition temperature, T_g, of the pure polymer component. The intensity of the new relaxation process increases with the content of MM and hence the relaxation process can be assigned to the segmental motion of the chains intercalated in the interlayers of MM. On the other hand, the relaxation time of the normal mode reflecting the fluctuation of the end-to-end vector is the same as the neat polymers but the intensity of the relaxation process increases due to enhancement of the internal electric field by MM.     

Synthesis of polyaniline/montmorillonite nanocomposites with an enhanced anticorrosive performance

Polyaniline/montmorillonite (PANI/Mt) nanocomposites (1–7% (w/w) Mt based on the aniline content) were synthesized by in situ chemical oxidative polymerization with a 73.4–75.8% monomer conversion level. Fourier-transform infrared and scanning electron microscopy analyses confirmed the presence of Mt incorporation into PANI, whilst X-ray diffraction analysis revealed the exfoliated structure and that PANI was intercalated between the Mt layers. Thermogravimetric analysis revealed that the thermal properties of PANI and PANI/Mt composites were enhanced with increasing Mt levels.     

Poly [2-(cinnamoyloxy)ethyl methacrylate-co-octamethacryl-POSS] nanocomposites: Synthesis and properties

Poly [2-(cinnamoyloxy)ethyl methacrylate-co-octamethacryl-POSS] nanocomposites were synthesized from octamethacryl-POSS and 2-(cinnamoyloxy)ethyl methacrylate (CEM) by free radical polymerization. The chemical structures and morphologies of these nanocomposites were determined by FTIR, ²⁹Si NMR, energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) techniques. The XRD data showed that the materials were amorphous in nature, indicating that POSS formed an aggregate instead of a crystalline form in the polymer matrix. The POSS-CEM nanocomposites exhibited high thermal stability. Excitation and emission of the CEM-incorporated POSS nanocomposites, studied in the solid state, exhibited blue emission with CIE (x, 0.178; y, 0.137) coordinates, in addition to an emission intensity that increased with increasing CEM (monomer) concentration.     

The effect of the solvent on the morphology of cellulose acetate/montmorillonite nanocomposites

Nanocomposites of cellulose acetate and sodium montmorillonite were prepared using the solution intercalation method with different solvents. The effects of solvent type on the morphology, thermal and mechanical properties of the nanocomposites were investigated by X-ray microtomography and diffraction, field emission scanning electron microscopy, analytical transmission electron microscopy based on electron loss spectroscopy imaging and dynamical mechanical analysis. XRD and TEM results indicated that the dispersion and delamination of the clay are achieved when the solvent presents favorable interactions with the clay. In this case, the storage modulus and the glass transition temperature are significantly higher than those of pure cellulose acetate. The results show that the solvent has a major effect in controlling the morphology of cellulose acetate and cellulose acetate nanocomposite and could be used as a process parameter to produce films with a range of properties.     

Studies on thermal properties of PS nanocomposites for the effect of intercalated agent with side groups

Polystyrene-layered silicate nanocomposites were prepared from three new organically modified clays by emulsion polymerization method. These nanocomposites were exfoliated up to 3 wt% content of pristine clay relative to the amount of polystyrene (PS). The intercalated agents C₂₀, C₂₀-4VB, and C₂₀-POSS intercalated into the galleries result in improved compatibility between hydrophobic polymer and hydrophilic clay and facilitate the well dispersion of exfoliated clay in the polymer matrix. Results from X-ray diffraction, TEM and Fourier transform infrared spectroscopy indicate that these intercalated agents are indeed intercalated into the clay galleries successfully and these clay platelets are exfoliated in resultant nanocomposites. Thermal analyses of polystyrene-layered silicate nanocomposites compared with virgin PS indicate that the onset degradation temperature ca. 25 °C increased and the maximum reduction in coefficient of thermal expansion (CTE) is ca. 40% for the C₂₀-POSS/clay nanocomposite. In addition, the glass transition temperatures of all these nanocomposites are higher than the virgin PS.     

The effect of incorporation of POSS units on polymer blend compatibility

In this work, the compatibility of poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymers with their polyhedral oligomeric silsesquioxane (POSS) copolymers combined by solution blending is investigated, to determine the effect of incorporation of the POSS unit on polymer compatibility. The morphology of these tethered POSS copolymer/polymer blends was studied by electron microscopy, thermal analysis, and density. Although the basic PS/PMMA blend was clearly immiscible, it was also found that the incorporation of POSS into the PS chain led to incompatibility when the POSScoPS copolymer was blended with PS homopolymer. However, conversely, in the case where the POSS moiety was included as part of a copolymer with PMMA, the copolymer was miscible with the PMMA homopolymer. The presence of isobutyl units on the corners of POSS cage is clearly sufficient to encourage miscibility with PMMA. Interestingly, blends of the two different POSS copolymers led to an immiscible structure, despite having the common POSS units, the interactions between the POSS moieties clearly not being sufficient to drive compatibility. The POSS copolymers have also been used as interfacial agents in immiscible PS and PMMA blend, and it has been found that the appearance of the interface bonding is improved, although the phase morphology is only slightly changed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of polybenzoxazine networks nanocomposites containing multifunctional polyhedral oligomeric silsesquioxane (POSS)

A new class of polybenzoxazine/POSS nanocomposites with network structure is prepared by reacting multifunctional benzoxazine POSS (MBZ-POSS) with benzoxazine monomers (Pa and Ba) at various compositional ratios. Octafunctional cubic silsesquioxane (MBZ-POSS) is used as a curing agent, which is synthesized from eight organic benzoxazine tethers through hydrosilylation of vinyl-terminated benzoxazine monomer (VP-a) with octakis(dimethylsiloxy)silsesquioxane () using a platinum complex catalyst (Pt-dvs). Incorporation of the silsesquioxane core into polybenzoxazine matrix could significantly hinder the mobility of polymer chains and enhance the thermal stability of these hybrid materials. For these nanocomposites, increasing the POSS content in the hybrids is expected to improve its thermal properties with respect to the neat polybenzoxazine. The morphology feature is useful to explain the thermal property changes (T_g and T_d) and AFM images show that the presence of POSS aggregation in larger scales occurs at higher POSS contents. The reason of the heterogeneous phase separation may be from the less compatibility of the inorganic silsesquioxane core with organic benzoxazine species and the homopolymerization of MBZ-POSS. In the course of the formation of the polybenzoxazine/POSS hybrids, POSS particles were separated from the polybenzoxazine rich region, leading to POSS rich domains in the range of 50-1000 nm.     

Effect of montmorillonite dispersion on flammability properties of poly(styrene-co-acrylonitrile) nanocomposites

Poly(styrene-co-acrylonitrile)/Cloisite 20A (95/5) nanocomposites, having various spatial dispersion levels of the clay, were prepared with controlling clay concentrations in a solvent by the coagulation method. X-ray diffraction, transmission electron microscopy and laser scanning confocal microscopy were used to characterize the structure and morphology of the nanocomposites on a nano-scale and on a micro-scale. Quantitative analysis of clay spatial dispersion in the nanocomposites based on the laser scanning confocal microscopy images was conducted from three different perspectives: 1) clay spatial distribution; 2) the non-clay-occupied domain size; and 3) the relationship between the frequency and intensity of pixels in the images. The results from these quantitative methods indicate that nanocomposites with different spatial dispersion levels of clay in the poly(styrene-co-acrylonitrile) matrix were obtained. Evidently, the ?d₀₀₁ data from the X-ray diffraction was found to be not useful in measuring the clay dispersion in the nanocomposites. The effect of clay dispersion on the flammability properties of the nanocomposites and relevant mechanism of the clay dispersion having influence on flammability were also investigated. In radiant gasification experiments at 50 kW/m², the best clay dispersion yielded a 32% reduction in peak mass loss rate, as compared to the nanocomposites with the worst dispersion.     

Intercalation and exfoliation relationships in melt-processed poly(styrene-co-acrylonitrile)/montmorillonite nanocomposites

The effects of surfactant structure on the morphology and mechanical properties of melt processed mixtures of poly(styrene-co-acrylonitrile) (SAN) with montmorillonite (MMT) organoclays were examined. The composite which exhibited the greatest change in gallery height, the highest modulus, and greatest aspect ratio (∼50) was produced from an organoclay with the lowest molecular weight surfactant, dimethyl hydrogenated tallow ammonium. For ammonium ion surfactants with ∼18 carbon hydrophobic tail(s), stack swelling, as measured by wide angle X-ray scattering (WAXS), was more strongly related to the reduced surfactant molecular weight than polarity or aromaticity of the head group substituents. A surfactant with a shorter tail length (∼12 vs. 18 carbon tail length) resulted in unswollen stacks in the composite.The swelling of the organoclay galleries seems to be explained by a balance of some favorable interactions of SAN with the montmorillonite platelet surface, versus repulsive mixing of aliphatic surfactant substituents with polar SAN. The repulsive nature of the latter increases as molecular weight of the head group substituents increases. A third factor is the platelet-platelet attraction that seems to explain the lack of swelling in the case of the shorter tail surfactant.Mechanical properties are also reported; and the composite moduli were found to compare to theoretical predictions using the Halpin-Tsai theory based on aspect ratios determined by transmission electron microscopy (TEM). The experimental aspect ratios do not seem to correlate with the WAXS gallery shifts. This and other evidence suggest that exfoliation in melt-processed SAN/MMT composites is not explained by intercalation behavior.     

Influence of montmorillonite layered silicate on plasticized poly(l-lactide) blown films

Plasticized poly(l-lactide) (PLA) montmorillonite layered silicate (MLS) nanocomposites were compounded and blown-film processed using a co-rotating twin screw extruder. PLA was mixed with 10 wt% acetyltriethyl citrate ester plasticizer and 5 wt% of an organically modified montmorillonite at various screw speeds. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) determined that the compounded pellets and the blown film PLA/MLS nanocomposites were intercalated. The effect of processing screw speeds on the barrier, thermal, mechanical, and biodegradation properties of the nanocomposites were analyzed and compared to the neat polymer. Nanocomposite films show a 48% improvement in oxygen barrier and a 50% improvement in water vapor barrier in comparison to the neat PLA. The thermogravimetric analysis (TGA) showed an overall 9 °C increase in the decomposition temperature for all of the nanocomposites. Differential scanning calorimetry (DSC) has determined that the glass transition, cold crystallization and melting point temperatures were not significantly influenced by the presence of MLS. Mechanical properties of the nanocomposites showed that the Young's modulus increased by 20% and the ultimate elongation of the nanocomposites were not sacrificed in comparison to the neat samples. Biodegradation rates in soil were slightly greater for the PLA/MLS nanocomposite than the pure PLA. However, none of the PLA pure and nanocomposites achieved significant biodegradation levels after 180 days.