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131.
Joo Batista A. Silva Regina C. M. de Paula Judith P. A. Feitosa Eduardo Diogo Gurgel‐Filho Claudio Maniglia‐Ferreira Francisco Jose de Souza Filho 《应用聚合物科学杂志》2006,100(5):4082-4088
Gutta‐percha cone is the most widely used material for root canal filling. The in vivo aging of this cone focus on the degradation of its main organic component, trans‐1,4‐polyisoprene, was studied. Aged cones (25 samples) from 2 to 30 years of root canal filling were extracted from different patients in the occasion of retreatment by mechanical way. The information about the aging time was given by the patients. Gel‐permeation chromatography (GPC) and infrared spectroscopy (FTIR) were the analytical techniques used. Polyisoprene degrades with time of aging, but in a slow process. Decrease in polymer molar mass from 5.7 × 105 to 1.7 × 105 g/mol was observed in polyisoprene from cone after 30 years of root canal filling and inside a noninfected tooth. In tooth with caries and periodontal infection, the decrease in molar mass is higher (4.6 × 104 g/mol in cone with 10 years of aging). The production of carbonyl and hydroxyl groups in the aged material indicates that the process is oxidative, even in closed teeth. In these cases, the oxygen could be provided from tissue fluid. The degradation mechanism is complex and depends on many factors, besides time of root canal filling. The dental problem caused by the aging could be the production and migration of cytotoxic substances to periodontal ligament and the reduction on the canal sealing property due to the polymer weight loss. Both of them could contribute to the root canal treatment failure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4082–4088, 2006 相似文献
132.
The mechanical property and phase structures of wheat proteins/polyvinyl alcohol blends studied by high-resolution solid-state NMR 总被引:1,自引:0,他引:1
The phase structures of thermally processed wheat proteins (WP) and polyvinyl alcohol (PVOH) blends were studied by solid-state high-resolution NMR spectroscopy. The intermolecular interactions among the multi-component systems and the behavior of each component in the blends on scales of nanometers were examined. The mechanical properties of the blends were also measured and related to the phase structure studies. The results indicated that the polymer chains of WP could be homogeneously mobilized when thermally processed with glycerol and water as plasticisers, but the glycerol predominately associated with WP rather than PVOH in the blends. The intermolecular hydrogen bonding interactions between WP and PVOH caused some extent of miscibility in the system on scales of nanometers especially when the PVOH content was low. The tensile strength and modulus of the blends were improved as compared to WP. However, the intermolecular interactions were relatively weak and could not be further enhanced by increasing PVOH component in the blends. The particle miscible WP/PVOH blends contained plasticised WP and PVOH phases in conjunction with the miscible WP/PVOH phase. Increasing the PVOH content in the blends did not result in an increase of the percentage of the miscible phase and the blends tented to be immiscible while the elongation of the blends was reduced when increasing the PVOH content in the blends. 相似文献
133.
134.
Yongpeng Xue 《Polymer》2005,46(18):7293-7300
Novel ionic naphthalene thermotropic polymers (NTPs) based on wholly aromatic copolyesters were synthesized, in which ionic monomer was introduced in the form of para-linked metal hydroquinone disulfonate (HQDS). These ionic NTPs contained ionic groups of up to 4 mol%, with counterions of either monovalent K or divalent Ca, and exhibited thermotropic liquid crystallinity. The K-salts exhibited the crystalline and liquid crystalline behaviors, typically observed for a non-ionic NTP; and they developed excellent thermal and mechanical properties. Testing was made as a function of ionic content under similar processing and testing conditions. The value of glass transition temperature rose as the average molecular weight increased. Both the melting temperature, Tm, and the crystallization temperature, Tc, remained nearly constant over the composition range studied. All the K-salt ionic NTPs showed enhanced tensile properties over a non-ionic NTP. The strength increased significantly as the ionic content increased despite the decrease in the molecular weight, reflecting the dominant effect of ionic interactions over the effect of molecular weight. Enhanced tensile properties arise from enhanced interchain interactions via ionic bonds (cross-links) between highly aligned NTP chains. The incorporation of HQDS-type ‘straight’ ionic units into a NTP copolyester can provide useful information about the effect of ionic interactions on the thermal/mechanical properties of NTPs. 相似文献
135.
Marcos R. Guilherme Adriano V. Reis Alexandre T. Paulino André R. Fajardo Edvani C. Muniz Elias B. Tambourgi 《应用聚合物科学杂志》2007,105(5):2903-2909
This contribution describes the absorption percentage of Pb2+ and Cu2+ from water by a superabsorbent hydrogel matrix (SH) made from an anionic polysaccharide copolymerized with acrylic acid (AAc) and acrylamide (AAm). Metal‐absorption tests, upon sequential pH variation, indicated that the SH has pH‐sensitivity for the absorption of both metals from solution, attributed to the functional ionic groups (? COOH) present in the AAc and arabic gum (AG) segments. At the pH 5.0, the SH exhibited good absorption capacity: 73.10% for Pb2+, 81.99% for Cu2+ in water and 63.64% for Pb2+, and 76.67% for Cu2+ in saline water with 0.1 mol kg?1 ionic strength. A replicated 22 full factorial design with a central point was built to evaluate the maximum absorption capacity of the metals into the SH. It was found that both the interaction and main effects of the pH and the initial concentration of metal solution on absorption percentage of the metals were statistically significant. Surface response plots indicated that the absorption capacity of both metals into the SH may be appreciably improved by using the solutions with lower initial concentration of metal and with higher pH values. Metal‐absorption results demonstrated that the SH is a convenient material for absorption of Pb2+ and Cu2+ from pure aqueous and saline aqueous environments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
136.
A surfactant‐free method to produce responsive polymer microgels is introduced. As an example, poly(methacrylic acid) hydrogels with varying crosslinking density have been synthesized in bulk and then chopped using a high shear mechanical cutter to form microgel particles dispersed in water. The mechanical cutting technique enables the concentration and particle size distribution of the microgel suspensions to be easily controlled, therefore making the rheology of the suspensions tuneable. The particle size distribution of the dispersions, characterized using light scattering, was dependent on the speed and duration of mechanical cutting. The particle size distribution also depended on the degree of crosslinking of the hydrogel. The higher the crosslinking density, the lower the average mean diameter of the resulting microgel particles. The lower the crosslinking density of the hydrogel, the larger the difference between the maximum and minimum particle size. The time to complete swelling of the particles upon change in pH was measured to be up to 45 s, depending on the particle size. The rheology of the resulting suspensions as a function of pH was investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 104: 1912–1919, 2007 相似文献
137.
The viscosity of polyacrylamide (PAM) dilute aqueous solutions with NaCl, glucose, and SDS as additives was measured by Ubbelohde viscometry. There was linear relationship between reduced viscosity vs. PAM concentration in aqueous solutions. The Huggins constant k and intrinsic viscosity [η] were used to study the conformation of the polymer chains and the degree of polymer–solvent interaction. In addition, the viscosity of diluted PAM solutions in water with acetone, ethanol, DMF, and ethylene glycol as cosolvent was measured. It was found that the polymer chain conformation contracted as the acetone, ethanol, and DMF cosolvent composition ratio increased, but there was no distinguishing difference between water–ethylene glycol compositions. The solution properties of PAM were used to estimate the swelling properties of PAM gel in the same external conditions, as gel is formed by crosslinking of linear polymer. In good solvent the polymer chain should be expanded, and gel is expected to have large swelling ratio. In water cosolvent systems, when the linear polymer chain underwent coil–globule transition, PAM gel should have volume phase transition under corresponding external conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3122–3129, 2003 相似文献
138.
The nanometer scale topography of self‐assembling structural protein complexes in animals is believed to induce favorable cell responses. An important example of such nanostructured biological complexes is fibrillar collagen that possesses a cross‐striation structure with a periodicity of 69 nm and a peak‐to‐valley distance of 4–6 nm. Bovine collagen type I was assembled into fibrillar structures in vitro and sedimented onto solid supports. Their structural motif was transferred into a nickel replica by physical vapor deposition of a small‐grained metal layer followed by galvanic plating. The resulting inverted nickel structure was found to faithfully present most of the micrometer and nanometer scale topography of the biological original. This nickel replica was used as a die for the injection molding of a range of different thermoplastic polymers. Total injection molding cycle times were in the range of 30–45 seconds. One of the polymer materials investigated, polyethylene, displayed poor replication of the biological nanotopographical motif. However, the majority of the polymers showed very high replication fidelity as witnessed by their ability to replicate the cross‐striation features of less than 5 nm height difference. The latter group of materials includes poly(propylene), poly(methyl methacrylate), poly(L ‐lactic acid), polycaprolactone, and a copolymer of cyclic and linear olefins (COC). This work suggests that the current limiting factor for the injection molding of nanometer scale topography in thermoplastic polymers lies with the grain size of the initial metal coating of the mold rather than the polymers themselves.
139.
It is suggested that some relaxation processes observed in crystalline polyethylene are consequences of the diffusive motion of a particular defect called a point dislocation or twist dispiration loop along the polyethylene stems in lamellar crystals. The motion of the defect, characterized by a diffusion coefficient and a mobility, is described by solutions of the Smoluchowski diffusion equation with boundary conditions that constrain the defect to move along routes that produce experimentally observable results. The fact that passage of the defect causes both a 180° rotation of the chain and moves an extra CH2 group in the direction of the chain axis is important to the interpretation of the data according to this model. The diffusion coefficient for a defect is estimated to be around 2 × 10?9 cm2 s?1 at 70°C. This value is shown to be reasonable both from the viewpoint of detailed computer modelling of defect motion and contemporary ideas about scaling. 相似文献
140.
Selwyn F. Mapolie John R. Moss Gregory S. Smith 《Journal of Inorganic and Organometallic Polymers》1997,7(4):233-250
A series of metal-containing vinylic monomers of the type
and
was homopolymerized using 2,2-azobisisobutyronitrile (AIBN) as the free-radical initiator. These monomers were also copolymerized with styrene in the presence of AIBN. These compounds represent a class of organometallic polymers in which the metal is bonded to the polymer backbone via a metal–carbon bond. The new compounds were characterized by IR and 1H NMR spectroscopy as well as scanning electron microscopy, gel permeation chromatography, and thermoanalytical studies (DSC and TGA). The properties of the new organometallic polymers are discussed. 相似文献