Preparation and characterization of photopolymerizable organic–inorganic hybrid materials by the sol-gel method

A series of UV-curable organic–inorganic hybrid materials were prepared by the sol-gel technique and coated onto Plexiglass^® substrate. The effects of the content of EGDMA and the content of the inorganic part on various properties of the coatings, such as tensile strength, hardness, gloss, and cross-cut adhesion, were investigated. It was found that the properties of the coating were improved by the addition of an inorganic part. The thermal properties of the hybrids were enhanced by incorporating silane sol into the organic part. Furthermore, it was found that the coating containing silica had a higher char content at 800 °C than the coating without silica. SEM studies indicated that nanosized (about 50 nm) silica particles were evenly dispersed throughout the organic matrix. A photo-DSC investigation showed that the organic coating polymerized more quickly than the hybrid coating.     

Synthesis and characterization of novel polyimide/SiO2 nanocomposite materials containing phenylphosphine oxide via sol‐gel technique

In this article, a series of novel polyimide/silica (PI/SiO₂) nanocomposite coating materials were prepared from tetraethoxysilane (TEOS), γ‐glycidyloxypropyltrimethoxysilane (GOTMS), and polyamic acid (PAA) via sol‐gel technique. PAA was prepared by the reaction of 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) and bis (3‐aminophenyl) phenyphosphine oxide (BAPPO) in N‐methyl‐2‐ pyrrolidone (NMP). BAPPO was synthesized hydrogenation of bis (3‐nitrophenyl) phenyphosphine oxide (BNPPO) in the presence of Pd/C. The silica content in the hybrid coating materials was varied from 0 to 20 wt %. The molecular structures of the composite materials were analyzed by means of FT‐IR and ²⁹Si‐NMR spectroscopy techniques. The physical and mechanical properties of the nanocomposites were evaluated by various techniques such as, hardness, contact angle, and optical transmission and tensile tests. These measurements revealed that all the properties of the nanocomposite coatings were improved noticeable, by the addition of sol‐gel precursor into the coating formulation. Thermogravimetric analysis showed that the incorporation of sol‐gel precursor into the polyimide matrix leads to an enhancement in the thermal stability and also flame resistance properties of the coating material. The surface morphology of the hybrid coating was characterized by scanning electron microscopy (SEM). SEM studies indicated that nanometer‐scaled inorganic particles were homogenously dispersed throughout the polyimide matrix © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Formulation and in vitro evaluation of bisphosphonate loaded microspheres for implantation in osteolysis

Chitosan and poly(lactide-co-glycolide) acid (PLGA) microspheres loaded with alendronate sodium (AS) were prepared for orthopedic as well as dental applications. In orthopedics the aim was to make the total joint prostheses stay in the body for a long time without causing bone tissue loss, while in dentistry it was aimed to treat the alveolar bone resorption caused by periodontitis and also to make the dental treatment using implants easier by reducing the bone loss in patients with osteoporosis. Solvent evaporation method was used to prepare AS loaded PLGA microspheres and emulsion polimerization method was used to prepare AS loaded chitosan microspheres. Particle size, loading efficacy, surface characteristics, and in vitro release characteristics were examined on prepared formulations. After the examination of the scanning electron microscopy photographs of microspheres, chitosan microspheres were observed to have spherical structure and smooth surface characteristics while PLGA microspheres were observed to have spherical porous surface structure. Loading efficacy was found to be 3.30% for chitosan microspheres and 7.70% for PLGA microspheres. It was observed that 85% of AS had been released at the end of the third day from chitosan microspheres whereas 58% was released at the end of the fifth day from PLGA microspheres. It was found that chitosan microspheres gave first order release while PLGA microspheres gave zero order release.     

The use of poly(ethylene oxide) as hydrogen donor in type II photoinitiated free radical polymerization

The aim of this study was to demonstrate hydrogen donating capability of poly(ethylene oxide) (PEO) in type II photoinitiated free radical polymerization for dental applications. Photopolymerization kinetics of the dental resin mixtures were monitored by Photo-DSC. H-NMR spectroscopic and GPC studies were also performed in order to gain insight to the hydrogen abstraction mechanism. The effect of molecular weight of PEO on the photoinitiation efficiency was investigated. Photolysis of solutions containing benzophenone and PEO in the presence of a radical scavenger namely, 2,2,6,6-tetramethylpiperidine-N-oxyl free radical (TEMPO) revealed that photoexcited benzophenone readily abstracts hydrogen from methylene groups present in PEO backbone. It was demonstrated that such photoinitiating system can be converted to a versatile grafting process. PEO possessing photochemically attached TEMPO units initiates the nitroxide mediated radical polymerization of styrene upon heating at 110 °C leading to the formation of poly(ethylene oxide-g-styrene) graft copolymer. Potential use of the photoinitiating system in dental formulations was also demonstrated. The polymeric nature, water solubility and nontoxicity make PEO a promising candidate as hydrogen donor in dental formulations.     

Effect of molecular weight on the dissolution properties of polystyrene latex films

An in situ steady-state fluorescence (SSF) technique was applied in order to study the dissolution process of polystyrene (PS) latex films. The effect of the molecular weight M _w of the PS on the dissolution rate was investigated. The PS chains were copolymerized with (1-pyrene)methyl methacrylate in order to make use of pyrene (P) as a fluorescent probe to monitor the dissolution process. Seven different films were prepared from P-labeled PS latex dispersions with different molecular weights at room temperature. These films were then annealed at 200 °C for 15 min to complete the film formation process before dissolution. The dissolution of PS films in a toluene (70 %)–cyclohexane (30 %) mixture was monitored in real time by watching the change in the fluorescence intensity of P, I _P. We used a model that included both case I and case II diffusion kinetics to interpret the results of the dissolution experiments. The relaxation constants k ₀ and the dissolution coefficients D _d of the polymer chains were measured. Two different dissolution coefficients were obtained, which were attributed to the small and long polymer chains in the film, considering the high polydispersity of the polymer. It was also found that both of the D _d values scaled with M _w according to the law D _d ≈ M ^?n .     

Rapid Growth Cone Uptake and Dynein‐Mediated Axonal Retrograde Transport of Negatively Charged Nanoparticles in Neurons Is Dependent on Size and Cell Type

Nanoparticles (NPs) are now used in numerous technologies and serve as carriers for several new classes of therapeutics. Studies of the distribution of NPs in vivo demonstrate that they can be transported through biological barriers and are concentrated in specific tissues. Here, transport behavior, and final destination of polystyrene NPs are reported in primary mouse cortical neurons and SH‐SY5Y cells, cultured in two‐compartmental microfluidic devices. In both cell types, negative polystyrene NPs (PS(?)) smaller than 100 nm are taken up by the axons, undergo axonal retrograde transport, and accumulate in the somata. Examination of NP transport reveals different transport mechanisms depending on the cell type, particle charge, and particle internalization by the lysosomes. In cortical neurons, PS(?) inside lysosomes and 40 nm positive polystyrene NPs undergo slow axonal transport, whereas PS(?) outside lysosomes undergo fast axonal transport. Inhibition of dynein in cortical neurons decreases the transport velocity and cause a dose‐dependent reduction in the number of accumulated PS(?), suggesting that the fast axonal transport is dynein mediated. These results show that the axonal retrograde transport of NPs depends on the endosomal pathway taken and establishes a means for screening nanoparticle‐based therapeutics for diseases that involve neurons.     

Functionalization of Isotactic Polypropylene with Citraconic Anhydride

Summary Functionalization of isotactic polypropylene i-PP) with citraconic anhydride (CA) was carried out in 1,2,4-trichlorobenzene solution with dicumyl peroxide as an initiator at 160 °C under nitrogen atmosphere.atmosphere. Chemical and physical structures and thermal behavior of the synthesized graft copolymers with different anhydride units were determined by volumetric titration (acid number), FTIR and ¹H-NMR spectroscopy, X-ray powder diffraction, DSC and TGA thermal analyses. It was shown that the crystallinity and thermal behavior of grafted i-PP’s depend on anhydride unit concentration in grafted i-PP; grafting reaction proceeds selectively which is not accompanied by oligomerization of CA and degradation main chain as in known maleic anhydride/PP system. This fact was explained by inhibition effect of α-methyl group in CA grafted unit on the chain β-scission reactions and no homopolymerization of CA in chosen grafting conditions. Functionalized i-PPs showed high thermal stability in comparison with virgin i-PP.     

The Effect of Gd Concentration on the Physical and Magnetic Properties of Bi1.7Pb0.3-xGdxSr2Ca3Cu4O12+y Superconductors

Bi–Pb–Gd–Sr–Ca–Cu–O bulk samples with nominal composition Bi_1.7Pb _0.3-xGd_xSr₂Ca₃Cu₄O_12+y (x=0.01, 0.05, 0.075, 0.10) were prepared by the melt-quenching method. The effects of different Gd doping on the structure have been investigated by electrical resistance, scanning electron micrographs, XRD, magnetization and magnetic hysteresis loop measurements. The magnetization measurements have been carried out as a function of magnetic field for fields up to 5 kOe at temperatures well below the zero resistance temperatures of the annealed samples. It has been found that the high-T_c superconducting phase, (2 2 2 3), is formed in the sample A with concentration x = 0.01, annealed at 840°C for 120 h. However, with increasing Gd³⁺ doping for Pb²⁺ the (2 2 2 3) phase gradually transforms into the (2 2 1 2) phase. The magnitudes of magnetization and initial susceptibility, | M | and | dM/dH|, and the hysteresis loop areas decrease with increasing Gd concentration x and/or temperature T. The fast decreases in | M|, | dM/dH |, and the hysteresis loop areas related to the superconducting volume, with increasing x and/or T seem to imply an existence of flux pinning centres in our samples. In order to support this implication the critical current densities J_c, of the samples, have been estimated at two fixed temperatures, 9 and 30 K. Our data have indicated that J_c decreases with increasing temperature and/or Gd concentration, as expected.     

Synthesis and characterization of flame retarding UV‐curable organic–inorganic hybrid coatings

UV‐curable, organic–inorganic hybrid materials were synthesized via sol–gel reactions for tetraethylorthosilicate, and methacryloxypropyl trimethoxysilane in the presence of the acrylated phenylphosphine oxide resin (APPO) and a bisphenol‐A‐based epoxy acrylate resin. The sol–gel precursor content in the hybrid coatings was varied from 0 to 30 wt %. The adhesion, flexibility, and hardness of the coatings were characterized. The influences of the amounts of inorganic component incorporated into the coatings were studied. Results from the mechanical measurements show that the properties of hybrid coatings improve with the increase in sol–gel precursor content. In addition, thermal properties of the hybrids were studied by thermogravimetric analysis in air atmosphere. The char yield of pure organic coating was 32% and that of 30 wt % silicate containing hybrid coating was 30% at 500°C in air atmosphere. This result demonstrates the pronounced effect of APPO on the flame retardance of coatings. Gas chromatography/mass spectrometry analyses showed that the initial weight loss obtained in thermogravimetric analysis is due to the degradation products of the photoinitator and the reactive diluent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1906–1914, 2006     

Effect of an Er,Cr:YSGG laser preparation on dentin bond strength of a universal adhesive

The aim of this study was to evaluate the bond strength of a universal adhesive system to dentin prepared with SiC paper or an Er,Cr:YSGG laser using different bonding strategies (etch-and-rinse versus self-etch mode). Ninety-six extracted caries-free, sound human molars were used. The teeth were longitudinally sectioned in the mesiodistal direction and were wet polished with 600-grit SiC paper to obtain a standardized flat dentin surface. All prepared teeth were randomly divided into two groups, according to the surface preparation method: GroupI:an erbium, chromium:yttrium,scandium, gallium, garnet laser; Group II: silicon carbide paper[SiC] (n = 48). Each group was then assigned into three subgroups according to the universal adhesive’s (Single Bond Universal) bonding strategies: (a) etch-and-rinse mode with phosphoric acid, (b) etch-and-rinse mode with a laser, (c) self-etch mode (n = 16). For surface preparation, the Er,Cr:YSGG laser was used at 3 W, 30 Hz with 140 μs pulse duration for 25 s. For etching mode, the laser was used at 1.5 W (60% air, 70% water). Cylinders of composite were fabricated on the bonding area and shear bond strength was determined using a universal testing machine. Failure modes were evaluated using a stereomicroscope. The data were analyzed using two-way ANOVA followed by the Bonferroni test (p < 0.05). Bonding strategies showed statistically significant differences in both the SiC-and laser-prepared groups (p < 0.05).Universal adhesive used in etch-and-rinse mode with acid showed significantly higher bond strength values than in self-etch mode (p < 0.05). The bond strength values did not differ according to the surface preparation method (p > 0.05). Irrespective of preparation method, using universal adhesive in etch-and-rinse mode with acid might improve dentin bond strength. Laser preparation did not affect the bond strength of the universal adhesive tested.