Polylactide compositions. II. Correlation between morphology and main properties of PLA/calcium sulfate composites

Starting from calcium sulfate (gypsum) as fermentation by‐product of lactic acid production process, high performance composites have been produced by melt‐blending polylactide (PLA, L/D isomer ratio of 96:4) and β‐anhydrite II (AII) filler, that is, calcium sulfate hemihydrate previously dehydrated at 500 °C. Characterized by attractive mechanical and thermal properties due to good filler dispersion throughout the polyester matrix, these composites are interesting for potential use as biodegradable rigid packaging. Physical characterization of selected composites filled with 20 and 40 wt % AII has been performed and compared to processed unfilled PLA with similar amorphous structure. State of dispersion of the filler particles and interphase characteristic features have been investigated using light microscopy (LM) and scanning electron microscopy (SEM). Addition of AII did not decrease PLA thermal stability as revealed by thermogravimetry analyses (TGA) and allowed reaching a slight increase of PLA crystallizability during melt crystallization and upon heating from the glassy, amorphous state (DSC). It was found by thermomechanical measurements (DMTA) that the AII filler increased pronouncedly storage modulus (E′) of the composites in comparison with PLA in a broad temperature range. The X‐ray investigations showed stable/unchanged crystallographic structure of AII during processing with molten PLA and in the composite system. The notable thermal and mechanical properties of PLA–AII composites are accounted for by the good filler dispersion throughout the polyester matrix confirmed by morphological studies, system stability, and favorable interactions between components. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2770–2780, 2007     

Functionalization of polyethylene/silane copolymers in posttreatment reactions

7‐Octenyldimethylphenylsilane was copolymerized with ethylene via Et(Ind)₂ZrCl₂ methylaluminoxane catalyst system without loss of catalyst activity or decrease in molar mass. The comonomer contents in the polymer samples were at a level of 0.15–1.0 mol % and the reactive phenylsilane groups were posttreated to different alcoxy‐ and halosilane groups, for example, Si? F, Si? Cl, Si? OCH₃, and Si? OCH₂CH₃. The posttreatment reactions had no major effect on the molar masses or on the thermal properties (measured with differential scanning calorimetry) of the copolymers. The reaction pathways were nearly independent of the comonomer contents and the reactions reached 70–100% conversions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1461–1467, 2004     

Toughness mechanism of polypropylene/elastomer/filler composites

The toughening mechanisms of polypropylene filled with elastomer and calcium carbonate (CaCO₃) particles were studied. Polypropylene/elastomer/CaCO₃ composites were prepared on a twin‐screw extruder with a particle concentration of 0–32 vol %. The experiments included tensile tests, notched Izod impact tests, scanning electron microscopy, and dynamic mechanical analysis. Scanning electron microscopy showed that the elastomer and CaCO₃ particles dispersed separately in the matrix. The modulus of the composites increased, whereas the yield stress decreased with the filler concentration. The impact resistance showed a large improvement with the CaCO₃ concentration. At the same composition (80/10/10 w/w/w), three types of CaCO₃ particles with average diameters of 0.05, 0.6, and 1.0 μm improved the impact fracture energies comparatively. The encapsulation structure of the filler by the grafting elastomer had a detrimental effect on the impact properties because of the strong adhesion between the elastomer and filler and the increasing ligament thickness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1113–1123, 2005     

Flame retardant epoxy composites with epoxy‐containing polyhedral oligomeric silsesquioxanes

A kind of polyhedral oligomeric silsesquioxanes (POSS) containing the propoxyl‐epoxy and phenyl groups (pr‐ep‐Ph‐POSS) was synthesized via hydrolytic condensation reaction. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry identified the structure of the pr‐ep‐Ph‐POSS, including major caged Si₆O₉ (T6), Si₁₀O₁₅ (T10), Si₁₂O₁₈ (T12), etc. The pr‐ep‐Ph‐POSS was applied into the epoxy resin to achieve EP/pr‐ep‐Ph‐POSS composites. Thermogravimetric analysis indicated that EP/pr‐ep‐Ph‐POSS showed excellent thermal properties than pure EP. The fire behaviors of EP/pr‐ep‐Ph‐POSS composites were evaluated based on the cone calorimetry, limiting oxygen index (LOI), UL‐94 vertical burning test, and smoke density test. The smoke density decreased by ~30%, the LOI value reached to 26.4%, dripping was inhibited, and the peak of heat release rate decreased by ~62%. X‐ray photoelectron spectroscopy analysis and FTIR indicated that protective‐barrier effect is the main flame‐retardant mode of action for pr‐ep‐Ph‐POSS, due to the formation of the Si‐O‐Si, Si‐O‐C, and Si‐C condensed phase, which improve the thermal stability, strength, and integrity of the char layer.     

Synthesis of polyethylene‐octene elastomer/SiO2‐TiO2 nanocomposites via in situ polymerization: Properties and characterization of the hybrid

In this study, a silicic acid and tetra isopropyl ortho titanate ceramic precursor and a metallocene polyethylene‐octene elastomer (POE) or acrylic acid grafted metallocene polyethylene‐octene elastomer (POE‐g‐AA) were used in the preparation of hybrids (POE/SiO₂? TiO₂ and POE‐g‐AA/SiO₂? TiO₂) using an in situ sol‐gel process, with a view to identifying a hybrid with improved thermal and mechanical properties. Hybrids were characterized using Fourier transform infrared spectroscopy, ²⁹Si solid‐state nuclear magnetic resonance (NMR), X‐ray diffraction, differential scanning calorimetry, thermogravimetry analysis, dynamic mechanical thermal analysis, and Instron mechanical testing. Properties of the POE‐g‐AA/SiO₂? TiO₂ hybrid were superior to those of the POE/SiO₂? TiO₂ hybrid. This was because the carboxylic acid groups of acrylic acid acted as coordination sites for the silica‐titania phase to allow the formation of stronger chemical bonds. ²⁹Si solid‐state NMR showed that Si atoms coordinated around SiO₄ units were predominantly Q₃ and Q₄. The 10 wt % SiO₂? TiO₂ hybrids gave the maximum values of tensile strength and glass transition temperature in both POE/SiO₂? TiO₂ and POE‐g‐AA/SiO₂? TiO₂. It is proposed that above this wt %, excess SiO₂? TiO₂ particles caused separation between the organic and inorganic phases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1690–1701, 2005     

Sizing effects on main relaxation process of cyanate ester glass fiber composites using dynamic mechanical and microthermal analyses

The influence of sizing/polymer interaction or interphase on dynamic mechanical relaxation properties of cyanate ester composites was investigated by means of dynamic mechanical analysis. The dynamic mechanical behavior of different samples (three types of composites with different sizing and neat resin) was analyzed by using two phenomenological models (TFV and WLF). Related coefficients such as C₁, C₂, and T_∞ (Vogel temperature) were evaluated. Results have shown that these parameters were strongly dependent on sizing state, therefore, on interphase. In addition, the frequency dependence of the molecular relaxation process was well described by the Cole‐Cole plot. These results were confirmed by the sizing extract/resin blend study. Microthermal analysis has shown that partial miscibility existed between resin and sizing extract. Local thermal analyses were carried out by positioning the probe over selected regions: bulk resin and sizing/resin blend. A decrease in resin glass‐transition temperature was observed in the sizing resin blend. The different results have shown that a local plasticization of resin by sizing occurred with crosslink density modification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 205–214, 2006     

Dynamic mechanical and dielectric properties of ORMOCER® incorporating functionalized poly(styrene) latexes

Organically modified aluminosilicate hybrid materials incorporating polystyrene and poly(styrene‐co‐hydroxypropyl acrylate) latexes, (3‐glycidyloxypropyl) trimethoxysilane, and aluminum sec‐butoxide [Al(O^sBu)₃] were synthesized by a sol–gel process. The bulk materials obtained were macroscopically homogeneous dispersions with good mechanical properties. Dynamic mechanical and dielectric analyses of these new hybrid materials as a function of the Al(O^sBu)₃ concentration and copolymer composition revealed a series of transitions that represented relaxation processes of the incorporated polymer (glass transition), ?Al? O? Si?, the ?Si? O? Si? part of the network, and segmental motion of unreacted ?Si? (CH₂)₃OCH₂CHCH₂O chains. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 860–867, 2001     

Control of thermoresponsive property of urea end‐functionalized poly(N‐isopropylacrylamide) based on the hydrogen bond‐assisted self‐assembly in water

The precise synthesis and variation in the thermoresponsive property based on the supramolecular assembly of a novel urea end‐functionalized poly(N‐isopropylacrylamide) (PNIPAM) were studied. A series of PNIPAMs with different diphenylurea groups at the chain end (X? Ph? NH? CO? NH? Ph? trz? PNIPAM: X = H, OCH₃, CH₃, NO₂, Cl, and CF₃) were synthesized by using a combination of the atom transfer radical polymerization and the copper(I)‐catalyzed azide‐alkyne cycloaddition. The cloud point of the obtained polymers depended on the hydrogen‐bonding ability of the introduced urea group. The ¹H NMR measurement suggested that the obtained PNIPAM assembled in water via the intermolecular hydrogen bonding by the terminal urea group. From the dynamic light scattering and transmission electron microscopy measurements, the aggregated nanoparticles of the resulting polymer were directly observed in water at a temperature below its cloud point. The hydrogen‐bonding property of the chain end urea group was concluded to be involved in the aggregation of the PNIPAM in water, leading to the variation in its cloud point. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6259–6268, 2009     

Novel antimicrobial polyethylene composites prepared by metallocenic in situ polymerization with TiO2‐based nanoparticles

Polyethylene (PE) composites with titanium oxide (TiO₂) nanoparticles were produced via in situ polymerization representing a novel route to obtain antimicrobial polymeric materials. The TiO₂ nanoparticles synthesized by the sol–gel method were used either as‐synthesized or modified organically with hexadecyltrimethoxysilane (Mod‐TiO₂). These particles were added, together with the catalytic system (formed by a metallocenic catalyst and methylaluminoxane as cocatalyst), directly to the reactor, yielding in situ PE composites with 2 and 8 wt % content of nanofiller. The catalytic polymerization activity presented a slight decrease with the incorporation of the TiO₂ and Mod‐TiO₂ nanoparticles compared to polymerization without filler. Regarding the properties of the composites, crystallinity increased slightly when the different nanofillers were added, and the elastic modulus increased around 15% compared to neat PE. PE/TiO₂ nanocomposites containing 8 wt % of TiO₂ exposed to UVA irradiations presented antimicrobial activity against Escherichia coli. The PE/Mod‐TiO₂ nanocomposite with 8 wt % filler killed 99.99% of E. coli, regardless of light and time irradiation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polypropylene/organoclay nanocomposites compatibilized with hydroxyl‐functional polypropylenes

The properties of polypropylene composites can be tailored through the use of nanoclay fillers. The effectiveness of a metallocene‐catalyzed hydroxyl‐functional polypropylene in the compatibilization of polypropylene layered nanosilicate composites was studied, and the results were compared with those for a commercial maleic anhydride functionalized polypropylene. Polypropylene/organoclay nanocomposites were prepared by melt blending, and two polypropylene/compatibilizer/organoclay ratios, 90/5/5 and 70/20/10, were characterized. The organomodification of the clay was carried out with octadecylamine and N‐methylundecenylamine. The structure of the layered silicate was studied by transmission electron microscopy, wide‐angle X‐ray scattering, and small‐angle X‐ray scattering. The fracture surfaces of the composites and thus the efficiency of the compatibilizers to penetrate the galleries of the organoclays were characterized by scanning electron microscopy, and the melt viscosity was studied by stress‐controlled rotational rheometry. The nanostructure was observed with both alkyl amines used for intercalation. The fillers facilitated the processability of all the composites, consisting of equal amounts of compatibilizer and organoclay filler and, in some of the composites, containing twice as much compatibilizer as organoclay filler. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1892–1903, 2005     

Preparation of nanoalumina/EPDM composites with good performance in thermal conductivity and mechanical properties

In this paper, nanoalumina (Al₂O₃) highly filled ethylene propylene diene monomer (EPDM) composites are prepared, and the mechanical (static and dynamic) properties and thermal conductivity are investigated systemically through various characterization methods. Furthermore, influences of in situ modification (mixing operation assisted by silane at high temperature for a certain time) with the silane‐coupling agent bis‐(3‐triethoxy silylpropyl)‐tetrasulfide (Si69) and stearic acid (SA) pretreatment on the nano‐Al₂O₃ filled composites are as well investigated. The results indicate that nano‐Al₂O₃ particles can not only perform well in reinforcing EPDM, but also improve the thermal conductivity significantly. Assisted by in situ modification with Si69, the mechanical properties (especially dynamic mechanical properties) of the nano‐Al₂O₃ filled composites are improved obviously, without influencing the thermal conductivity. By comparing to the traditional reinforcing fillers, such as carbon black (grade N330) and silica, in situ modified nano‐Al₂O₃ filled composites exhibit excellent performance in mechanical (static and dynamic) properties as well as better thermal conductivity, especially lower compression heat build‐up and better fatigue resistance. In general, our work indicates that nano‐Al₂O₃, as the novel thermal conductive reinforcing filler, is suitable to prepare rubber products serving in dynamic conditions, with the longer expected service life. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface‐modified hydroxyapatite linked by L‐lactic acid oligomer in the absence of catalyst

A new surface modification method of hydroxyapatite nanoparticles (n‐HA) by surface grafting reaction of L ‐lactic acid oligomer with carboxyl terminal (LAc oligomer) in the absence of any catalyst was developed. The LAc oligomer with a certain molecular weight was directly synthesized by condensation of L ‐lactic acid. Surface‐modified HA nanoparticles (p‐HA) were attested by Fourier transformation infrared spectroscopy, ³¹P MAS‐NMR, and thermal gravimetric analysis (TGA). The results showed that LAc oligomer could be grafted onto the n‐HA surface by forming a Ca carboxylate bond. The grafting amount of LAc oligomer was about 13.3 wt %. The p‐HA/PLLA composites showed good mechanical properties and uniform microstructure. The tensile strength and modulus of the p‐HA/PLLA composite containing 15 wt % of p‐HA were 68.7 MPa and 2.1 GPa, respectively, while those of the n‐HA/PLLA composites were 43 MPa and 1.6 GPa, respectively. The p‐HA/PLLA composites had better thermal stability than n‐HA/PLLA composites and neat PLLA had, as determined by isothermal TGA. The hydrolytic degradation behavior of the composites in phosphate buffered saline (PBS, pH 7.4) was investigated. The p‐HA/PLLA composites lost their mechanical properties more slowly than did n‐HA/PLLA composites in PBS because of their reinforced adhesion between the HA filler and PLLA matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5177–5185, 2005     

Solid mechanochemical preparation of core‐shell SiO2 particles and their improvement on the mechanical properties of PVC composites

In this article, a solid mechanochemical route to prepare core‐shell structured particles was introduced. X‐ray photoelectron spectrum, transmission electron microscope and dissolving experimental results indicated the formation of [(inorganic particle)/(elastomer)] core‐shell structured particles. The thermal stable experiments showed that untreated SiO₂ can cause dehydrochlorination of poly(vinyl chloride) (PVC) and discoloration of PVC/SiO₂ composites and the formation of core‐shell structured SiO₂ particles will improve the thermal stability of PVC/SiO₂ composites. The mechanical properties and rheological results showed that the formation of core‐shell structured SiO₂ particles can both improve the mechanical and processing properties of PVC/SiO₂ composite. ACR in PVC/(SiO₂‐PMMA‐ACR) composites acted not only as toughener for PVC matrix but also as cushion breaker if the content of ACR is enough. Meanwhile compared with other SiO₂ particles the formation of core‐shell structured SiO₂ particles can decrease the apparent viscosity, increase the critical shear rate and improve the appearance of extrudes of PVC/SiO₂ composites. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 938–948, 2008     

Poly(vinyltriethoxysilane) modified MWCNT/polyimide nanocomposites—Preparation,morphological, mechanical,and electrical properties

Multi‐walled carbon nanotube (MWCNT) modified by vinyltriethoxysilane (VTES) via free radical reaction has been prepared (poly (vinyltriethoxysilane) modified MWCNTs, PVTES‐MWCNT). Precursor of polyimide, polyamic acid has been synthesized by reacting 4,4′‐oxydianiline with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride. PVTES‐MWCNT were then mixed with polyamic acid and heated to 300 °C to form CNT/polyimide composite. During the imidization processes, the silanes on CNT surface reacted with each other and may be connected together by covalent bond (Si? O? Si). The PVTES‐MWCNT was analyzed by Fourier transform infrared and X‐ray photoelectron spectroscopy. The PVTES‐MWCNT/polyimide composites were analyzed by CP/MAS solid state ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. Morphological properties of the PVTES‐MWCNT/polyimide composites were investigated by scanning electron microscope and transmission electron microscope. Electrical conductivity increased dramatically comparing to the unmodified MWCNT/polyimide composites. Mechanical properties of nanocomposite were enhanced significantly by PVTES‐MWCNT. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 803–816, 2008     

Structural and mechanical behavior of polypropylene/ maleated styrene‐(ethylene‐co‐butylene)‐styrene/sisal fiber composites prepared by injection molding

Hybrid composites consisting of isotactic poly(propylene) (PP), sisal fiber (SF), and maleic anhydride grafted styrene‐(ethylene‐co‐butylene)‐styrene copolymer (MA‐SEBS) were prepared by melt compounding, followed by injection molding. The melt‐compounding torque behavior, thermal properties, morphology, crystal structure, and mechanical behavior of the PP/MA‐SEBS/SF composites were systematically investigated. The torque test, thermogravimetric analysis, differential scanning calorimetric, and scanning electron microscopic results all indicated that MA‐SEBS was an effective compatibilizer for the PP/SF composites, and there was a synergism between MA‐SEBS and PP/SF in the thermal stability of the PP/MA‐SEBS/SF composites. Wide‐angle X‐ray diffraction analysis indicated that the α form and β form of the PP crystals coexisted in the PP/MA‐SEBS/SF composites. With the incorporation of MA‐SEBS, the relative amount of β‐form PP crystals decreased significantly. Mechanical tests showed that the tensile strength and impact toughness of the PP/SF composites were generally improved by the incorporation of MA‐SEBS. The instrumented drop‐weight dart‐impact test was also used to examine the impact‐fracture behavior of these composites. The results revealed that the maximum impact force (F_max), impact‐fracture energy (E_T), total impact duration (t_r), crack‐initiation time (t_init), and crack‐propagation time (t_prop) of the composites all tended to increase with an increasing MA‐SEBS content. From these results, the incorporation of MA‐SEBS into PP/SF composites can retard both the crack initiation and propagation phases of the impact‐fracture process. These prolonged the crack initiation and propagation time and increased the energy consumption during impact fracture, thereby leading to toughening of PP/MA‐SEBS/SF composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1214–1222, 2002     

Enhanced Thermal Stability in SiO2/Carbon Filler Derived from Rice Husk via Microwave Treatment for Electronic Packaging Application

Here we report the effect of microwave treatment on a silica–carbon (SiO₂ /C) filler derived from rice husk and the function of the microwave‐treated filler in an epoxy matrix for electronic packaging applications. Thermogravimetric analysis revealed improved thermal stability of the SiO₂ /C filler upon microwave treatment. X‐ray diffraction analysis indicated partial SiC formation after the microwave treatment. For packaging applications, compared to that of the pure epoxy polymer, the thermal conductivity of the epoxy–SiO₂ /C composite was improved by 178% at 40 wt % content of the microwave‐treated SiO₂ /C filler. Furthermore, an improvement of 149% in storage modulus and 17.6°C in glass transition temperature of the epoxy–SiO₂ /C composites was realized. The improvement in thermal stability of SiO₂ /C filler could be achieved via a simple microwave treatment, which in turn enhanced the thermal stability, thermal conduction, and thermomechanical strength of the electronic packaging materials.     

Inhibition of acid‐induced decomposition of diphenyltriazenes by complexation with cyclodextrins

Acid‐promoted N? N bond cleavage in 1,3‐diphenyltriazenes (X‐Ph‐N=N‐NH‐Ph‐X; X = H, 4‐OCH₃), leading to formation of diazonium ions and anilines, is strongly inhibited in aqueous solutions in the presence of cyclodextrins (CDs). The inhibition is ascribed to the formation of inclusion complexes that render the guest diphenyltriazene significantly less basic as a result of the less polar nature of the CD cavity (a microsolvent effect). Association equilibrium constants for 1:1 host–guest complexes increase in the order α‐CD <β‐CD ～ permethyl‐β‐CD < hydroxypropyl‐β‐CD, with values for X = 4‐OCH₃ being larger than those for X = H. In the case of α‐CD, formation of 2:1 host–guest complexes is also involved. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 567–574, 2010     

Molecular orientation,crystallinity, and flexural modulus correlations in injection molded polypropylene/talc composites

In order to promote better understanding of the structure‐mechanical properties relationships of filled thermoplastic compounds, the molecular orientation and the degree of crystallinity of injection molded talc‐filled isotactic polypropylene (PP) composites were investigated by X‐ray pole figures and wide‐angle X‐ray diffraction (WAXD). The usual orientation of the filler particles, where the plate planes of talc particles are oriented parallel to the surface of injection molding and influence the orientation of the α‐PP crystallites was observed. The PP crystallites show bimodal orientation in which the c‐ and a*‐axes are mixed oriented to the longitudinal direction (LD) and the b‐axis is oriented to the normal direction (ND). It was found that the preferential b‐axis orientation of PP crystallites increases significantly in the presence of talc particles up to 20 wt% in the composites and then levels‐off at higher filler content. WAXD measurements of the degree of crystallinity through the thickness of injection molded PP/talc composites indicated an increasing gradient of PP matrix crystallinity content from the core to the skin layers of the molded plaques. Also, the bulk PP crystallinity content of the composites, as determined by DSC measurements, increased with talc filler concentration. The bulk crystallinity content of PP matrix and the orientation behavior of the matrix PP crystallites and that of the talc particles in composites are influenced by the presence of the filler content and these three composite's microstructure modification factors influence significantly the flexural moduli and the mechanical stiffness anisotropy data (E_LD/E_TD) of the analyzed PP/talc composites. Copyright © 2009 John Wiley & Sons, Ltd.     

1‐Silacyclopent‐2‐enes and 1‐silacyclohex‐2‐enes bearing functionally substituted silyl groups in 2‐positions. Novel electron‐deficient Si?H?B bridges

The reactions of alkyn‐1‐yl(vinyl)silanes R₂Si[C?C‐Si(H)Me₂]CH?CH₂ [R = Me (1a), Ph (1b)], Me₂Si[C?C‐Si(Br)Me₂]CH?CH₂ (2a), and of alkyn‐1‐yl(allyl)silanes R₂Si[C?C‐Si(H)Me₂]CH₂CH?CH₂ (R = Me (3a), R = Ph (3b)] with 9‐borabicyclo[3.3.1]nonane in a 1:1 ratio afford in high yield the 1‐silacyclopent‐2‐ene derivatives 4a, b and 5a, and the 1‐silacyclohex‐2‐ene derivatives 6a, b, respectively, all of which bear a functionally substituted silyl group in 2‐position and the boryl group in 3‐position. This is the result of selective intermolecular 1,2‐hydroboration of the vinyl or allyl group, followed by intramolecular 1,1‐organoboration of the alkynyl group. In the cases of 4a, b, potential electron‐deficient Si? H? B bridges are absent or extremely weak, whereas in 6a,b the existence of Si? H? B bridges is evident from the NMR spectroscopic data (¹H, ¹¹B, ¹³C and ²⁹Si NMR). The molecular structure of 4b was determined by X‐ray analysis. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of the properties of waterborne polyurethane/multiwalled carbon nanotube and acid‐treated multiwalled carbon nanotube composites prepared by in situ polymerization

A series of waterborne polyurethane (WBPU)/multiwalled carbon nanotube (CNT) and WBPU/nitric acid treated multiwalled carbon nanotube (A‐CNT) composites were prepared by in situ polymerization in an aqueous medium. The optimum nitric acid treatment time was about 0.5 h. The effects of the CNT and A‐CNT contents on the dynamic mechanical thermal properties, mechanical properties, hardness, electrical conductivity, and antistatic properties of the two kinds of composites were compared. The tensile strength and modulus, the glass‐transition temperatures of the soft and hard segments (T_gs and T_gh, respectively), and ΔT_g (T_gh − T_gs) of WBPU for both composites increased with increasing CNT and A‐CNT contents. However, these properties of the WBPU/A‐CNT composites were higher than those of the WBPU/CNT composites with the same CNT content. The electrical conductivities of the WBPU/CNT1.5 and WBPU/A‐CNT1.5 composites containing 1.5 wt % CNTs (8.0 × 10⁻⁴ and 1.1 × 10⁻³ S/cm) were nearly 8 and 9 orders of magnitude higher than that of WBPU (2.5 × 10⁻¹² S/cm), respectively. The half‐life of the electrostatic charge (τ_1/2) values of the WBPU/CNT0.1 and WBPU/A‐CNT0.1 composites containing 0.1 wt % CNTs were below 10 s, and the composites had good antistatic properties. From these results, A‐CNT was found to be a better reinforcer than CNT. These results suggest that WBPU/A‐CNT composites prepared by in situ polymerization have high potential as new materials for waterborne coatings with good physical, antistatic, and conductive properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3973–3985, 2005