Electroinduced dispersion polymerization of acrylonitrile in the presence of poly(acrylic acid) and catalytic amount of CE(IV)

Electroinduced dispersion polymerization of acrylonitrile initiated by Ce(IV) was performed in an electrolytic cell in the presence of poly(acrylic acid) (PAA). Micron‐size polyacrylonitrile (PAN) particles were stabilized with PAA by electrostatic interaction or by a PAA–Ce(III)–PAN ternary complex formation. A PAA–PAN stable polymer was formed in the cathodic compartment, and the reduced initiator was reoxidized in the anode, thus allowing for the continuation of the process. A possible mechanism of polymerization is suggested. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 723–728, 2002; DOI 10.1002/app.10076     

Influence of Surface Finish on Flexural Strength and Microhardness of Indirect Resin Composites and the Effect of Thermal Cycling

This study investigated the effect of surface finish and thermal cycling procedures on flexural strength and surface microhardness of three indirect resin composites, Artglass®, Signum®, and Solidex®. The specimens were prepared in sufficient number and size according to flexural and microhardness test requirements (n = 10). Scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analysis was also used for studying the morphology, dispersion, and elemental compositions of fillers. The EDX results showed that Artglass contained 1.57% aluminium oxide (Al₂O₃), 53.29% silicon dioxide (SiO₂), and 2.62% barium oxide (BaO); Signum had 55.69% silicon dioxide (SiO₂) and Solidex had 44.99% silicon dioxide (SiO₂) of total mass. Artglass appeared to display the best flexural strength values under all the test conditions employed (range: 116.8 ± 32.18 to 147.8 ± 47.97 MPa), and it was followed by Signum (range: 93.7 ± 22.84 to 118.0 ± 33.45 MPa). Thermal cycling did not seem to have affected the flexural strength of Artglass and Signum (p > 0.05); however, it led to a significant decrease, from (110.5 ± 20.69 MPa) to 74.0 ± 13.30 MPa (p < 0.001), in the strength of polished Solidex specimens. While surface microhardness of the three materials increased by polishing (Artglass: 55.7 ± 2.64/74.1 ± 8.63 Vickers Hardness Numbers (VHN); Signum: 44.8 ± 3.12/60.7 ± 4.50 VHN; Solidex: 44.0 ± 2.31/53.4 ± 3.58 VHN for unpolished/polished specimens), thermal cycling had a deleterious effect on this property (p < 0.001).     

Effect of Argon Plasma Pretreatment on Tensile Bond Strength of a Silicone Soft Liner to Denture Base Polymers

This study evaluated the effect of argon plasma treatment on tensile bonding of heat-cured and auto-polymerized acrylic resins prior to the processing of a silicone soft liner. Both types of polymethylmethacrylate (PMMA) resins were treated with argon plasma for 1 min or 10 min (n = 5). A control group, including untreated resin specimens, was also formed. After processing of the soft liner, the specimens were deflasked and stored dry for 24 h, and they were then subjected to tensile bond strength testing. In order to see the plasma effect on the resin surface chemistry, representative specimens were analysed by XPS. Highest tensile bond strengths were observed in the 1-min exposure group for each resin, and 10-min exposure yielded the lowest bond strength likely due to the damaging effect of the plasma treatment. XPS analysis showed that the O/C ratios increased greatly in treated samples and that the binding energy values were not significantly changed.     

Syntheses of electroactive layers based on functionalized anthracene for electrochromic applications

A new monomer (DTAT) was synthesized via linking 3,4-ethylenedioxythiophene (EDOT) on anthracene. The polymer, P(DTAT) was electrosynthesized by anodic oxidation of the corresponding monomer in 0.1 M LiClO₄ acetonitrile (ACN) solution. The optical properties, the absorption spectra and the kinetics, were examined. Spectroelectrochemical analysis showed that P(DTAT) has an electronic band gap (due to π-π* transition) of 1.57 eV at 776 nm.Copolymers of DTAT with EDOT were prepared in ACN/LiClO₄ (0.1 M) solvent-electrolyte couple by varying applied potential. The incorporation of an EDOT into the full conjugated backbone, DTAT, affects its optical behavior resulting in different colors; a claret red neutral state, gray and red intermediate states and a blue oxidized state.     

Emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate using nonionic emulsifiers in loop reactor

Batch emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate (VAc/2EHA = 90 : 10) was initiated by the thermal initiators ammonium persulfate and potassium persulfate at 70°C in the presence of nonylphenol ethoxylates with varying chain lengths and poly(vinyl alcohol). VAc–2EHA copolymer latexes were synthesized as two different series in a loop reactor. The first series was initiated by ammonium persulfate, and the second series was initiated by potassium persulfate. The influence of the counterions or initiators and chain lengths of a nonionic emulsifier on the properties of VAc–2EHA copolymer latexes were determined by measuring the viscosities, weight‐average molecular weights, number‐average molecular weights, molecular weight distribution, and surface tension of latexes to air. The results for the copolymer latexes indicated that some of their physicochemical properties increased with increasing chain length of the nonionic emulsifier, but some of them followed a different trend for the two initiators. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1380–1384, 2005     

Effects of Er,Cr:YSGG laser parameters on dentin bond strength and interface morphology

Previous studies have shown the effects of Er,Cr:YSGG laser irradiation on the dentin bond strength; but there are few reports that show the significance of the irradiation with different laser parameters on dentin bond strength and interface morphology. This in‐vitro study attempted to evaluate the microtensile bond strength (μTBS) and interface morphology of resin‐dentin interfaces, either followed by treatment with Er,Cr:YSGG laser irradiation with different parameters or not. The flattened dentin samples of 35 bovine teeth were embedded into acrylic blocks and randomly divided into seven groups according to surface treatments using Er,Cr:YSGG lasers with different parameters: 3 W/20 Hz, 3 W/35 Hz, 3 W/50 Hz, 1.5 W/20 Hz, 1.5 W/35 Hz, 1.5 W/50 Hz, or no laser treatment (n = 5). Composite buildups were done over bonded surfaces and stored in water (24 hours at 37°C). Specimens were sectioned into sticks that were subjected to μTBS testing and observed under FE‐SEM. Control groups (27.70 ± 7.0) showed statistically higher values than laser‐irradiated groups. There were no significant differences among laser groups. Despite that, increasing the pulse frequency yielded slightly higher bond strength. Depending on laser settings, Er,Cr:YSGG laser irradiation caused interfacial gaps and resin tags with wings morphology. With the parameters used in this study, Er,Cr:YSGG laser irradiation promoted morphological changes within resin‐dentin interfaces and negatively influenced the bond strength of adhesive systems. Microsc. Res. Tech. 78:1104–1111, 2015. © 2015 Wiley Periodicals, Inc.