A dual‐cure latex is prepared by mixing an amide‐functionalized latex with a latex that has both acetoacetoxy and unsaturated acrylic functionalities. The amide‐functionalized latex provides a thermal cure with the acetoacetoxy groups of the other latex via Michael addition. The partially polymerized triacrylates in the acrylate‐functionalized latex provide active sites for photocuring. Thermoset latex films are prepared by blending amide‐ and acrylate‐functionalized latexes in varying amounts. The effect of the photosensitizer (camphorquinone) concentration on thermal and mechanical properties is studied. The highest tensile modulus and elongation is observed in a 50:50 wt% amide/acrylate‐functionalized latex blend.
The influence of the chemical structure of styrene/butyl acrylate latexes on some properties of ordinary Portland cement mortars has been investigated for low fractions of polymer with respect to the amount of cement. The structural parameters that were varied included the presence of carboxylic surface charges, the nature of the surfactant system, the molecular weight of the non‐ionic emulsifier, and the particle surface coverage. The first part of the study showed that sterically stabilised latexes remain colloidally and chemically stable for several hours in the cement interstitial medium. Moreover, no interaction could be shown between cement and latex components. Then, for a fraction of about 5wt.‐% of polymer, no significant influence of the presence of the latex was observed on the end‐use properties of the mortars. However, it clearly appears that the use of a fraction of anionic stabiliser is highly detrimental to the paste workability, whereas this latter property is improved by the presence of non‐ionic surfactant due to steric repulsion forces. Finally, the microstructure analysis confirms that the particles are homogenously dispersed in the mineral matrix and that they remain smooth and spherical.
Transparent polyimide (PI) and chemically modified graphene nanocomposite films are prepared from solutions of pyromellitic dianhydride (PMDA)/4,4′‐oxydianiline (ODA) poly(amic acid) with various amounts (0.2–0.8 wt%) of graphene carboxylic acid (GCA) in DMAc. The GCA is synthesized by modifying chemically oxidized graphene (COG) with many carboxylic acid groups (–COOH) and is well‐dispersed in DMAc, the organic solvent most frequently used for PI synthesis. The GCA sheets in the PI/GCA composite films are well‐dispersed and aligned two‐dimensionally in the direction parallel to the PI films, which enhances the mechanical properties of the nanocomposite films.
A range of bio‐based rubbery thermosets have been synthesized by the cationic copolymerization of conjugated soybean oil, styrene, and 1,5‐hexadiene or isoprene as flexible crosslinkers. The thermal, and mechanical properties, as well as the wear behavior, of these new bio‐rubbers are reported. The amount of styrene and the type of diene incorporated have the greatest influence on the properties of the final materials. The largest variations are found in glass transition temperature, storage modulus, tan δ values, crosslink density, and abrasive wear depth, while thermal degradation and extraction analyses showed minimal variations with changes in composition.
A new route for the manufacturing of silica/poly(benzimidazole) (PBI) nanocomposites fibers is described. PBI was synthesized via melt polycondensation and polycondensation in poly(phosphoric acid). Solutions of PBI and silica nanoparticles in N,N‐dimethylacetamide (DMAc) were electrospun to fibers and non‐wovens. The resulting materials were analyzed by ATR‐IR spectroscopy, small‐angle X‐ray scattering (SAXS) and nitrogen sorption measurements. The non‐wovens could be processed towards dense, cross‐linked membranes by hot pressing and treatment with p‐xylylene dichloride.
Summary: This study investigated the physico‐mechanical properties, odor and VOC emission of bio‐flour filled PP bio‐composites with different pozzolan contents. On increasing the pozzolan content, the tensile and flexural strengths of the bio‐composites were not significantly changed, whereas the impact strength and water absorption increased slightly and the odor intensity decreased due to the absorption of thermal degradation gases of PP and bio‐flour at the pore surface of the pozzolan. The VOC emission of the bio‐composites, analyzed by GC‐MSD, was mainly due to PP oxidation and the thermal degradation of bio‐flour during the extrusion process at high manufacturing temperatures. With increased pozzolan content, other organic compounds of the bio‐composites were not significantly changed, but the toluene emission of the bio‐composites was decreased. SEM and SEM/EDX mapping techniques were employed to investigate the porous form and the pozzolan distribution in the bio‐composites. From these results, we concluded that the addition of pozzolan in the bio‐composites was an effective method for reducing their odor and VOC emission without any reduction in mechanical properties.
Summary: Acrylic rubber showed greatly improved mechanical properties and very nice elasticity when blended with small amount of PVDF. PVDF crystallized into very sparse and loose spherulites in the blends with ACM molecular chains incorporated into the PVDF lamellae. These micro‐crystals were precisely dispersed in the ACM matrix and acted as the physical crosslink points for the matrix upon stretching. Therefore, the ACM/PVDF blends containing small amounts of PVDF display the typical properties of thermoplastic elastomers with large elongation at break, high tensile strength, and excellent strain recovery from the highly deformed state.
Schematic diagram of physically crosslinked ACM by the tiny PVDF crystals in ACM‐rich PVDF/ACM blends. 相似文献
Summary: Different styrene‐ and acrylate‐based organic‐inorganic polymer composites incorporating magnesium hydroxide were successfully synthesized using MPTMS as a coupling agent and MgCl2 as an inorganic precursor. The polymer composites were prepared by free‐radical emulsion polymerization following different procedures. The samples were investigated by means of FT‐IR spectroscopy, XRD, TGA, DSC, and rheometry. It is shown that the preparation method does only affect the ratio of organic to inorganic component, but not the chemical structure of the composites. The obtained polymer composites consist of Mg(OH)2 particles which are linked covalently via MPTMS groups to the polymer backbone.
Scheme of Mg(OH)2 crosslinked with MPTMS units as proposed for the emulsion polymer composite. 相似文献
Summary: Various output heaters were extruded with CB‐filled HDPE composites. The effects of crystallinity on the PTC and thermal reproducibility of the quenched, annealed, and E‐beam crosslinked heaters were examined during heating and cooling cycles at an applied voltage of 220 V. Conductor resisitivity and PTC effect of the heaters increased as crystallinity of composites increased. During the thermal cycling test, significant changes in heater‐output and resistivity for annealed and quenched heaters were observed. However, for quenched/E‐beam radiated and annealed/E‐beam radiated heaters no significant difference was found. These results indicate that the annealing process did not affect the thermal and electrical reproducibility of HDPE/CB heaters significantly.
Acetylene black aggregates in polyethylene matrix. 相似文献
An in situ lubrication dispersion method is developed to achieve electrical conductivity in PP containing a small amount of MWCNTs. Good dispersion of the MWCNTs in PP is observed even after a short mixing time because the interactions between the entangled nanotubes are reduced. By in situ lubrication dispersion, the electrical percolation threshold of the PP nanocomposite can be as low as 0.5–0.7 wt% MWCNT. Rheological data also support percolation at 0.5 wt% MWCNT. With 0.5 wt% MWCNT, the slope of G′ at low frequency approaches unity and shows non‐terminal behavior. The proposed dispersion method enhances the wetting of MWCNTs and improves MWCNT dispersion compared to both direct mixing of MWCNT powder with a polymer melt and conventional master batch dilution.
Hybrid polymeric inlays, patterned by nanoimprint lithography, are used to rapidly mass replicate pillar‐like nanostructures by injection moulding. This is difficult to achieve with traditional nickel inlays due to the rapid heat transfer of the metal, which results in premature cooling of the molten polymer and improper filling of nanoscale features. Using hybrid inlays, nanopillars can reliably be stretched by up to 40% of their designed height by adjusting moulding parameters. Hybrid inlays display longevity of more than 2000 cycles and can rapidly be fabricated to firmly establish injection moulding as an exceptionally useful tool for the high volume prototyping and production of nanopatterned polymeric devices.
The depletion of selected substituted phenol stabilizers from systems simulating self‐etching dental adhesives is studied. If the adhesive monomer is an acrylate derivative, the stabilizer disappears quickly. Experimental results support the hypothesis that the phenol stabilizers are depleted from the system via a non‐radical reaction with the acrylic double bond in addition to the free‐radical mechanism. The C‐conjugate addition of aryloxide anions to the acrylate double bonds (the Michael reaction) is proposed as the reaction mechanism. The rate of the acid‐catalyzed Michael addition between acrylate monomers and phenolic stabilizers depends on the strength of the acidic catalyst.
A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
An amphiphilic LCBC PEO‐b‐PAz consisting of flexible PEO as a hydrophilic block and poly(methacrylic acid) containing an azobenzene moiety in side chain as a hydrophobic LC segment was synthesized and used to fabricated microporous films by spin‐coating method under a dry environment. With the help of a small amount of water, well‐arranged ellipsoidal micropores embedded in a LC matrix were obtained and the pore size is in the range of several tens µm of water. The influence of water content and rotational speed was studied in detail. It was found that regularly patterned microporous films can be prepared with certain water content, and the pore size can be easily tailored through changing the rotational speed. The obtained microporous structures showed good thermal and photo stability.
Polyurethanes with narrow‐disperse (ND) and polydisperse (PD) hard segment (HS) distributions were prepared in a two‐step process. First, a poly(propylene oxide) end‐capped with MDI (4,4′methylenebis(phenyl isocyanate) was synthesized. To this prepolymer either a diamine–diamide was added to form ND HSs or a mixture of a diamine–diamide and additional MDI to form PD HSs in the copolymers. The polyurethanes displayed a ribbon‐like crystalline morphology, and it was found that the copolymers with ND HSs were more crystalline, had a higher modulus, a less temperature‐dependant modulus, and a higher melting temperature than their PD counterparts. Overall, the polyurethanes with the narrow‐dispersed HSs displayed superior properties.
A nanocellular PS/PMMA polymer blend foam was prepared, where bubble nucleation was localized in the PMMA domains. The blend, which contains dispersed nanoscale PMMA islands, was prepared by polymerizing MMA monomers in a PS matrix to form highly dispersed PMMA domains in the PS matrix by diffusion mixing. The resulting blend was foamed with CO2 at room temperature. A higher depressurization rate at lower foaming temperature made the bubble diameter smaller and the bubble density larger, and a higher PS composition in the blend resulted in a larger bubble density. A void with 40–50 nm in average diameter and a pore density of 8.5 × 1014 cm?3 was obtained as for the finest nanocellular foams.
Summary: A novel hyperbranched poly(β‐ketoester) was synthesized from 2‐(acetoacetoxy)ethyl acrylate by the Michael addition in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as catalyst. 1H NMR integration experiments revealed that the degree of branching in the poly(β‐ketoester) was remarkably high at a level of 82.9%. The number‐average molecular weight of the polymer was between 2 100 and 12 000 and increased with reaction temperature and conversion.
Synthesis of hyperbranched polymer by Michael addition of AAEA. 相似文献
The crystallization behavior of a polyamide 6/organo‐modified montmorillonite (PA 6/OMMT) nanocomposite has been investigated by scanning chip calorimetry and wide‐angle X‐ray scattering, with emphasis placed on the evaluation of the effect of supercooling/cooling rate on the crystal/mesophase polymorphism of the PA 6 matrix. Presence of OMMT has negligible effect on the kinetics of formation of α‐crystals of PA 6 at low cooling rate while there is observed enhanced nucleation of γ‐mesophase on fast cooling. Furthermore, addition of OMMT leads to a distinct increase of the cooling rate required to completely vitrify the amorphous state. The performed experiments demonstrate that the nucleating effect of OMMT in PA 6/OMMT nanocomposites is of particular importance at cooling conditions relevant in polymer processing.
Summary: Biomimetic scaffolds are appealing products for the repair of bone defects using tissue engineering strategies. The present study prepared novel biomimetic composite scaffolds with similar composite to natural bone using bioactive glass, collagen, hyaluronic acid, and phosphatidylserine. The microstructure, swelling ratio, biodegradability, and biomineralization characteristic of the composite scaffolds with and without hyaluronic acid and phosphatidylserine were compared and analyzed by SEM/EDAX, XRD, and FTIR techniques and in vitro test, and the properties can be influenced by 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC)/N‐hydroxysuccinimide (NHS) crosslinking. The optimized properties of the crosslinked composite scaffolds observed in this study show the possibility of their use of bioactive and bioresorbable scaffolds in bone tissue engineering.
SEM micrographs of BG‐COL‐HYA‐PS composite scaffolds after immersion in SBF for 1 d. 相似文献
A procedure for the production of carbon nanotube (CNT) reinforced poly(vinylidine difluoride) (PVDF) powders has been developed. These powders are versatile precursors for a range of nanocomposite materials. The morphology of the CNT/PVDF powder can be related to the interaction between filler and matrix, which depends on the degree of modification of the polymer with grafted maleic anhydride (MAH‐graft‐PVDF). The mechanical performance of the nanocomposite containing 2.5 wt.‐% CNT and 1.25 ppm of MAH increased in tensile modulus, tensile strength, and strain to failure by 34, 30, and 22%, respectively, as compared to PVDF.
