Low‐crystalline random and gradient P(EO‐co‐PO) copolymers and amorphous PPO and PBO of high molecular weight were synthesized by anionic coordination polymerization. Polymer gel electrolytes based on these (co)polymers were prepared and tested for long‐term performance of DSSC. The DSSC based on P(EO‐co‐PO) copolymers have longer life time compared to the homo‐PEO‐ and homo‐PPO‐based DSSC, respectively. The cells containing the chemically crosslinked copolymer gel exhibited a high efficiency of 6% after 25 d performance, whereas the solar cells based on physically crosslinked copolymer gel showed fast degradation.
TMC/LLA copolymers with several TMC/LLA ratios are synthesized and a composite is obtained by reinforcing with short PLGA fibers. In vitro degradation is studied at 37 °C in pH = 7.4 buffer and compared with a PLLA homopolymer. The degradation of the copolymers appears slower than that of PLLA, showing that TMC units are more resistant to hydrolysis than LLA. Compositional changes indicate a preferential degradation of LLA units as compared to TMC ones. Morphological changes with crystallization of degradation by‐products are observed. The composite degrades much faster than the neat copolymer and PLLA because the faster degradation of PLGA fibers speeds up the degradation of the matrix. The composite appears promising for the fabrication of totally bioresorbable stents.
A new completely biodegradable shape‐memory elastomer consisting of PLLCA reinforced by in situ PGA fibrillation is described. The manufacturing processes and shape‐memory effects of the composites are discussed. DMA results reveal a strong interface interaction between in situ PGA fibrillation and PLLCA. Compared with the SMP‐based composites that are commonly used, the shape‐memory test shows that in situ PGA fibrillation can improve the recovery properties of PLLCA; in fact, the shape‐recovery rate increases from 80.5 to 93.2%.
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.
Two propylene copolymers with similar comonomer content and molecular weight were electrospun from solution. The 1‐octene and 1‐decene copolymers yielded ribbon‐like fibers. Isotactic poly(propylene) prepared by both heterogeneous and homogeneous catalyst systems could not be electrospun from the same solvent system used for the copolymers. The presence of the higher 1‐alkene comonomers in small amounts (about 1 mol‐%) not only affects the crystallinity of the polymer compared to the homopolymer, but appears to influence the solubility as well. The combined effect of lowering crystallinity and increasing solubility indicates that the use of higher 1‐alkene comonomers in low amounts could be a route to prepare poly(propylene) based electrospun fibers.
PHBV is produced by bacteria as intracellular carbon storage. It is advantageous concerning biocompatibility and biodegradability, but its low crystallization rate hinders the melt‐processing of fibers. This problem can be overcome by combining PHBV with PLA in a core/sheath configuration and introducing a new spin pack concept. The resulting PHBV/PLA bicomponent fibers show an ultimate tensile stress of up to 0.34 GPa and an E‐modulus of up to 7.1 GPa. XRD reveals that PLA alone is responsible for tensile strength. In vitro biocompatibility studies with human fibroblasts reveal good cytocompatibility, making these fibers promising candidates for medical therapeutic approaches.
Soft coatings are widely used to tailor the surface chemistry of materials without altering their bulk properties. However, the strength of adhesion between the coating and the substrate must be high enough for long‐term applications. This has become a major challenge in the medical field, especially for polymer‐coated stents, mainly due to several coating failures reported after mechanical expansion during clinical implantation. In this work, the applicability of current polymer‐metal adhesion tests to polymer‐coated stents is discussed. The small punch test was proposed as an adhesion test that allows fundamental studies on the adhesion and coating properties. This adhesion test was applied to thin fluorocarbon coatings deposited by plasma on 316L stainless steel.
Syntheses of eight novel methacrylates bearing phosphonic acid groups were synthesized in three to five steps. The interaction of these monomers with hydroxyapatite was investigated using 13C‐NMR spectroscopy. Free radical homopolymerizations were carried out in a mixture ethanol/water (2.5/1, v/v) using 2,2′azo(2‐methylpropionamidine) dihydrochloride as initiator. The copolymerization of these monomers with a mixture HEMA/GDMA (5/3, mol/mol) was investigated by photo‐DSC. Dentin shear bond strength measurements showed that 2‐methacryloyloxy‐3‐(1,1,2,2‐tetrafluoroethoxy)propylphosphonic acid 4b , 2,3‐dimethacryloyloxypropylphosphonic acid 18 and 3‐(methacryloyloxy)‐2,2‐(di[(dihydroxyphosphoryl)methyl])propyl methacrylate 23 are promising candidates for dental adhesives.
Copolymers of poly(2,5‐benzimidazole) (ABPBI) and poly[2,2′‐(p‐phenylene)‐5,5′‐bibenzimidazole] (pPBI) were synthesized for use as fuel cell membranes to take advantage of the properties of both constituents. The composition of the copolymers were controlled by changing the feed ratio of 3,4‐diaminobenzoic acid and terephthalic acid with 3,3′‐diaminobenzidine in the polycondensation reaction. The copolymer membranes showed higher conductivities, better mechanical properties, and larger acid absorbing abilities than commercial poly[2,2′‐(m‐phenylene)‐5,5′‐bibenzimidazole] membranes.
A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.
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.
We demonstrate solution blending of PVDF with PECA obtained by controlled polymerization of ECA. This method circumvents the processing detriments posed by the instant cross‐linking of CAs when encountering aprotic solvents such as DMF, a common PVDF solvent. The slower polymerization of ECA was tracked using NMR spectroscopy. The polymer mixture solutions were spin‐coated to study the film morphology, wettability, and surface energy. The polymer films show strong contribution of basic polar surface energy that can be beneficial in biomedical applications. DSC and TGA were also performed on the blended polymers. The DSC thermograms show clear suppression of PVDF melting point, which provides evidence of two‐polymer miscibility.
Nanostructuration of maleate and orthophthalic unsaturated polyester (UP) resins was achieved by the use of high molecular weight amphiphilic PBA‐b‐P(MMA‐co‐DMA)2 triblock copolymers. PBA is fully immiscible in cured UP resins, and the miscibility of P(MMA‐co‐DMA) random copolymers can be ensured with a minimum DMA content of 12 mol‐%. When using the triblock copolymers, fully transparent and nanostructured thermosets are obtained with a minimum DMA content in the outer blocks; the value of which is higher than 12 mol‐% and depends on the UP chemical structure. Finally, the fracture toughness of nanostructured thermoset was evaluated: for a triblock copolymer content as low as 5 wt.‐%, a 50% increase of KIc was obtained, as compared to the neat thermoset.
Glass fiber biobased composites have been prepared by ROMP of a commercially available vegetable oil derivative possessing an unsaturated bicyclic moiety, and DCPD. The resins and the corresponding composites have been characterized thermophysically and mechanically. Higher DCPD content yields materials with higher glass transition temperatures. Glass fibers significantly improve the tensile modulus of the resin from 28.7 to 168 MPa. These biobased composites utilize only a limited amount of a petroleum‐based monomer, while employing substantial amounts of a renewable resource.
The influence of the flow history experienced during injection molding on the mechanical properties of amorphous polymers is investigated. It is demonstrated that flow‐induced molecular orientation only causes a small anisotropic effect on the yield stress, which can be regarded as insignificant with respect to its absolute value. Its influence on the post‐yield strain‐hardening response is also shown to be imperceptible, in contrast to a orientation which is applied during deformation below the glas transition.
An aqueous dispersion of gold nanoparticles was added to an acrylic resin and UV‐cured. The photopolymerization process was followed by means of real‐time FT‐IR spectroscopy. Nanostructured coatings containing a homogeneous dispersion of gold nanoparticles with an average size range of 20–25 nm were achieved. Macroscopic aggregation during polymerization was avoided due to the rapid initiation and kinetic associated with the photopolymerization technique, which allowed the medium to quickly solidify around the dispersion particles.
Both α‐cyclodextrin and linear dextrin are used to prepare biocomposites with poly(3,4‐ethylenedioxythiophene). Materials are prepared electrochemically in aqueous solution. Comparison with the pure polymer indicates that the electroactivity and electrostability decrease with the incorporation of the dextrins while the electrical conductivity is retained. The different properties of the two biocomposites suggest that the linear dextrin is mainly located at the surface, whereas the cyclodextrin is homogeneously distributed in the polymeric matrix. Cell adhesion and proliferation assays indicate that the cellular activity is significantly higher in the dextrin‐containing biocomposites.
New talc/PBAT hybrid materials were prepared through reactive extrusion. First, PBAT was free‐radically grafted with MA to improve the interfacial adhesion between PBAT and talc. Then, the resulting MA‐g‐PBAT was reactively melt‐blended with talc through esterification reactions of MA moieties with the silanol functions from talc. Sn(Oct)2 and DMAP were used as catalysts. Interestingly, the tensile properties for these compatibilized composites were improved due to a better interfacial adhesion between both partners. XPS showed the formation of covalent ester bonds between the silanol functions from talc particles, and the MA moieties grafted onto the polyester backbones.
Poultry feather fiber is transformed into biothermoplastics using a twin screw extruder, and the plasticizing effect of four different plasticizers on the material properties is investigated. Conformational changes, viscoelastic behavior, thermal degradation, and phase transitions are assessed by means of FTIR spectroscopy, DMA, TGA, and DSC, respectively. The mechanical properties of the plasticized resins are assessed by tensile measurements, while optical transmittance is recorded using UV‐Vis spectrophotometry. The water uptake behavior of the fiber keratin and plasticized resins is also investigated.
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.
