Polymerization rate and copolymerization parameters of the free‐radical copolymerization of AMPS with 1‐VIm was studied as a function of the monomer feed and the pH value in ethanol. It was found that neutral and basic monomer mixtures containing the sodium salt of AMPS polymerized faster and led to polymers with a higher proportion of NaAMPS incorporated than those monomer mixtures containing the free acid. Additionally, based on the experimental data, copolymerization parameters of rAMPS = 0.3 and r1‐VIm = 0.13 were calculated for polymerization in acidic solution and rAMPS = 4.1 and r1‐VIm = 0.1 for polymerization in basic and neutral solutions. Finally, the thermal stability, rheological behavior, and intrinsic viscosity were determined for the polymers.
Chemical modification of EVOH in the molten state at 185 °C by a grafting from process of poly(ε‐caprolactone) in batch was studied. 1H NMR was used to characterize the structure evolutions of PCL grafts. In addition to grafting reactions, dynamic covalent transesterification reactions between EVOH residual alcohols and the polyester grafts led to a redistribution of the PCL grafts length. up to 27 and SR up to 80% were obtained. Experiments made in a corotating mini twin‐screw extruder also confirmed these results. The effect of the alcohol to caprolactone ratio and catalyst concentration (SnOct2) on kinetic evolution showed that few minutes were necessary to complete the polymerization. A kinetic model was proposed and adequate conditions for the synthesis by reactive extrusion were defined.
High‐performance nanocomposites of NaCMC with GO are produced by solution casting. FESEM images reveal a good homogeneous dispersion of GO in the NaCMC matrix. The composite formation is facilitated by H‐bonding interaction between GO and NaCMC. Tg of the composites increases with increasing GO concentration. The storage modulus (G′) exhibits a maximum 174% increase over NaCMC at 1 wt% GO. The mechanical properties of the composites exhibit highest increase of tensile stress and Young's modulus of 188 ± 4% and 154 ± 11%, respectively, for 1 wt% GO. Analysis of Young's modulus (Ey) data using the Halpin‐Tsai equation suggests that the Ey data are close to the unidirectional orientation at >0.5 wt% GO, indicating more efficient load transfer at these compositions.
EVOH‐g‐PCL were prepared by a solvent‐free reactive extrusion process using a co‐rotating twin screw extruder. Kinetic simulations were made of selected reaction conditions at 185 °C. Changes in the screw rotation rate resulted in evolution of the residence time distribution and slightly changed the monomer conversion. An increase of the [OH]0/[Cl]0 ratio made the reactive system more viscous and decreased the overall pumping capacities of the extruder. Increase of the mean residence time, combined with a positive kinetic effect of [OH]0 increase, leaded to an important increase in conversion. For all the conducted experiments, equivalent distribution dispersions and good agreements between calculated conversion and those measured were obtained. An increase in temperature from 185 to 200 °C resulted in total conversion.
The first reported use of two‐dimensional mesh thermoplastic fibers in an epoxy matrix for mendable composites is presented, yielding 100% restoration of GIC, failure energy, and peak loads over repeated damage‐healing cycles. SEM imaging and EDS mapping showed different surface structures between CFRPp and CFRPf and confirmed strength recoveries were attained by delivery of EMAA to the fracture plane which enabled the fractured surfaces to rebind after heating to 150 °C for 30 min.
This is the first report on a thermoformable bionanocomposite based on a natural nanocrystal and formed by grafting long polymer chains onto the surface of microcrystalline cellulose. For the cellulose nanocrystal‐graft‐poly(ε‐caprolactone), the “graft from” strategy contributed to long and dense “plasticizing” PCL tails onto the CN surface as the key of thermoforming. The grafted PCL chains shielded the hydrophilic surface of CN and, hence, showed high water‐resistance. Moreover, a strategy for developing new bionanocomposite materials based on natural nanocrystals has been presented.
Graft copolymers with a poly(ethylene‐co‐1‐octene) backbone and poly(methyl methacrylate) random polymer branches are successfully synthesized by the grafting‐from technique in the molten state. The in situ radical polymerization of methyl methacrylate from the polyolefin backbone is investigated with two different peroxide initiators at 135 and 150 °C, respectively. The number of PMMA grafts per polyolefin chain is varied from 0.08 to 1.07 with PMMA polymerization degrees of 500 and 18, respectively, depending on the experimental conditions. The effect of a nitroxyl‐based radical scavenger (i.e., DEPN) on competition between the grafting of PMMA from the polyolefin backbone and MMA homopolymerization is also explored.
The oxidative degradation of PP/OMMT nanocomposites under γ‐irradiation was studied. Changes in structure and properties resulting from γ‐exposure in the range 0–100 kGy were investigated. The results were analyzed by comparing the influence of PP‐g‐MA and pristine OMMT on the oxidation kinetics of neat PP. γ‐Irradiation in the presence of air strongly degraded the properties of PP materials, particularly for radiation doses above 20 kGy. The rate of oxidative degradation of PP/OMMT/PP‐g‐MA nanocomposites was much faster than that of neat PP. This suggests that PP‐g‐MA and pristine OMMT components behave as oxidation catalysts, leading to the formation of free radicals in the polymer matrix.
Poly(ε‐caprolactone) (PCL) was grafted to the surface of starch nanocrystals (StN) via microwave‐assisted ROP. The resultant nanoparticles were then incorporated into a poly(lactic acid) matrix to produce fully‐biodegradable nanocomposites with good mechanical properties. A loading level of 5 wt.‐% StN‐g‐PCL resulted in simultaneous enhancements of strength and elongation. The StN‐g‐PCL self‐aggregated as rubbery microparticles to enhance the elongation by ca. 10‐fold over that of neat PLA. Meanwhile, the grafted PCL chains were miscible with PLA and formed a stress‐transferring interface to the StN, providing a reinforcing function.
Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO5 nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO5 mineral pre‐treated by AlMe3, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.
SEM image of the fractured surface of a PCL‐TiNbO5 nanocomposite film. 相似文献
Capillary thinning experiments of semi‐dilute solutions of schizophyllan in water and DMSO are performed to determine the relaxation behavior in extensional flows as experienced, for example, in the flow through porous media in enhanced oil recovery. The extensional relaxation time λE is found to scale with concentration following a dissimilar power‐law dependency for the two solvents, λE ∝ c1.52 in water and λE ∝ c0.90 in DMSO. It is shown that the extensional flow fields are strong enough to break, and prevent the rebuilding of, intermolecular structures, due to hydrogen bonding that was observed to alter the viscoelastic response in shearing flows of aqueous schizophyllan solutions.
Summary: Two distinct types of polymer electrolyte membranes for conducting protons and lithium ions have been prepared by a radiation‐induced grafting method. The polymer electrolyte precursor (PVDF‐g‐PS) is obtained by the simultaneous grafting of styrene onto poly(vinylidene fluoride) (PVDF) followed by one of two specific treatments. This includes sulfonation with a chlorosulfonic acid/dichloromethane mixture to obtain proton (H+)‐conducting membranes, or activation with LiPF6/EC/DC liquid electrolyte to obtain lithium ion (Li+)‐conducting membranes. The chemical structure of the obtained electrolyte membranes is verified by FT‐IR spectroscopy. Differential scanning calorimetry is used to examine the changes in the crystallinity and the thermal properties of both electrolyte membranes during the preparation process. The thermal stability of both electrolyte membranes is also evaluated using thermal gravimetrical analysis. The obtained polymer electrolyte membranes achieve superior conductivity values: 1.61 × 10?3 S · cm?1 for Li+ and 5.95 × 10?2 S · cm?1 for H+ at room temperature at a polystyrene content of 50%. The results of this work suggest that high quality H+‐ and Li+‐conducting membranes can be obtained using a single radiation‐induced grafting method.
Schematic representation of the single root for preparation of Li+‐ and H+‐conducting membranes started by radiation‐induced grafting of styrene onto a PVDF film followed by chemical treatment. 相似文献
A new class of PLGA‐based materials suitable for the production of biodegradable NPs via free‐radical polymerization is proposed. ROP of lactide and glycolide using HEMA is carried out; macromonomers (HEMA‐LxGyA) with short PLGA chain ends are successfully produced. Afterwards, monomer‐starved semi‐batch emulsion polymerization of these HEMA‐LxGyA macromonomers is performed to obtain NPs with a low polydispersity index and a controlled size. The stability and degradability of NPs is confirmed from degradation studies that verify the possibility of tuning the degradation time by changing macromonomer characteristics such as chain length and composition.
Toughness enhancement of S‐(S/B)‐S triblock copolymers via a molecular‐weight‐controlled pathway is demonstrated. The post‐yield crack toughness behavior of the triblock copolymers uniquely reveal a brittle‐to‐semiductile‐to‐ductile transition with increasing while keeping the basic molecular architecture fixed. TEM and SAXS investigations indicated three distinct morphologies as a function of χeffN as a consequence of the increase in : (i) a homogeneous structure without phase‐separation, (ii) a weakly segregated structure, and (iii) a lamellar structure. The increase in crack toughness is also reaffirmed from kinetic and strain field analysis studies concerning dynamics of crack growth in block copolymers with high PS content.
Aminated poly(propylene) was prepared by reacting aliphatic primary diamines with maleic‐anhydride‐functionalized poly(propylene) by in situ melt reaction. Around 60–70% of the initial acid groups had reacted to form amide and imide groups as confirmed by the almost complete disappearance of the maleic anhydride peak in FT‐IR spectra. The molecular weight of the diamines had an influence on changes in molecular structure of the PP‐g‐NH2 as a result of secondary reactions such as chain extension and cross‐linking. PP‐g‐NH2 and polycarbonate were pressed into two‐layer films and their adhesion strength was measured. The results showed that PP‐g‐NH2 was a very effective adhesion promoter.
Acrylate‐based nanocomposite coatings prepared from uniformly sized, nanoscaled inorganic, i.e., BaSO4‐ and CaF2‐ as well as organometallic, i.e., Al‐maleate‐derived nanoparticles were prepared applying photochemical curing. Excellent mechanical and thermal stability as well as high optical transparency was achieved as compared to standard SiO2‐based coatings. The performance of CaF2‐based nanocomposites could be further enhanced by addition of nanocorundum. A comprehensive data set on surface and Martens hardness, the penetration depths, glass transition temperatures, and UV–Vis transparency of the final coatings is presented.
End‐grained wood/polyurethane composites were obtained by a water‐based one‐pot process free of diisocyanates. Wood was impregnated with both PEG and CBC‐functionalized PEG as a coupling agent. A thorough study of the CBC‐mediated end‐groups conversion of PEG was achieved. It came out that functionalization conditions strongly affected the polyurethane chain extension and its grafting onto the wood structure. Antiswelling efficiency measurements showed that the one‐pot procedure allowed to reach comparable dimensional stabilization than the diisocyanate‐based process previously described. Morphological analysis demonstrated that such an improvement was attributable to the formation of cell wall‐bulked WPCs.
The ability to incorporate medium chain length poly(hydroxyalkanoate) (mcl‐PHA) in the styrene miniemulsion polymerization process was investigated. As a result, novel poly(hydroxyalkanoate)‐co‐poly(stryrene) (PHA‐co‐PS) copolymers were synthesized in the form of stable organic–organic hybrid latexes. Evidence of chemical grafting of mcl‐PHA and cross‐linking of the PHA grafts was obtained using NMR, differential scanning calorimetry (DSC), gel extraction, and rheological analysis. A high degree of mcl‐PHA grafting was achieved by maintaining proper miniemulsion polymerization conditions throughout the course of the polymerization. The incorporation of PHA grafts was a function of the level of PHA in the formulations as well as the reaction conditions, as evidenced by solvent extraction and rheological analysis. DSC showed shifts in the Tg of PS towards higher temperatures, indicating chemical interaction of PS‐PHA.
Summary: VP and co‐monomers DMAAm and ST were successfully grafted onto a PP fabric in an emulsion copolymerization process initiated by γ‐radiation. The radiation dose, concentration of VP, the ratio of VP/DMAAm and VP/ST in the reaction solution, and the reaction temperature dependent graft copolymerization were investigated. The order of dependence of the initial rate of grafting on the radiation dose was found to be in the range of 1.2 to 0.93 for VP; 0.84 to 0.70 for VP/DMAAm and for VP/ST was in the range of 0.59 to 0.41. The activation energy of the graft copolymer reaction was determined to be 40.18 J · mol?1 for 0.464 mol · L?1 VP. In the case of co‐monomer mixtures (VP/DMAAm: 0.464/0.5) the energy of activation was noticeably higher at 49.71 J · mol?1 while for VP/ST (0.464/0.436) the activation energy was same as that of VP. XRD results showed that overall crystallinity significantly decreased with the increase of graft weight with a noticeable change in the chemical structure of the PP, indicating that the graft copolymer reaction was taking place both in the amorphous and crystalline regions of PP. A similar characteristic behavior was also obtained by DSC, which revealed the presence of an endotherm process in the range of 25 to 130 °C depending on the degree of grafting, attributed to the grafted chains of the monomer/co‐monomers. In order to determine the graft copolymer reaction of VP, DMAAm and ST onto the backbone of PP, the reaction products were characterized by FTIR spectroscopy. A good correlation was found between changes of crystallinity and level of graft copolymerization as determined by WAXRD and DSC.
Typical XRD traces of as‐received PP fabric (PPF) and grafted with VP (PPF‐g‐VP). 相似文献
This study concerns with the investigation of the effect of irradiation conditions on grafting of styrene into FEP films by the pre‐irradiation method. EPR spectroscopy was used to characterize the base polymer material regarding the trapped radical species and their concentration. Radiation‐induced changes in the chemical structure were studied by IR spectroscopy. Tensile strength and elongation at break as well as yield of grafting were found to be strongly influenced by irradiation temperature. Main‐chain scissions were identified to be the reason for the deterioration of the mechanical properties after radiation treatment at temperatures below glass transition temperature.
