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Curing Rate (curing + rate)
Selected AbstractsInfluence of whitening on the degree of conversion of dental adhesives on dentinEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2006Milena Cadenaro The aim of this study was to analyze the extent of polymerization of different adhesive systems on whitened dentin. One adhesive of each class was investigated: Adper Scotchbond Multi Purpose (3M ESPE); One-Step (Bisco); Clearfil Protect Bond (Kuraray); and Xeno III (Dentsply DeTrey). Dentin disks were treated with Opalescence Xtra Boost (Ultradent) for 30 min and bonded immediately after 24 h or after 14 d of storage in 100% humidity at 37°C. Unbleached dentin disks were prepared as controls. The extent of polymerization of bonded interfaces was obtained with differential scanning calorimetry (DSC) at 20, 40 and 60 s, and the data were statistically analyzed. The extent of polymerization obtained from DSC exotherms of adhesives applied immediately after whitening was significantly lower compared with controls. An increased extent of polymerization after storage was confirmed for all adhesives, and no difference with controls was found after 14 d. A prolonged irradiation time increased the curing rate for all the tested adhesives. This study supports the hypothesis that polymerization of the adhesive is reduced after dentin whitening and that delayed adhesive application reverses the polymerization inhibition. Prolonged polymerization intervals may counteract the inhibition of polymerization caused by the whitening procedure. Nevertheless, further in vivo studies should validate this issue. [source] New thermosets obtained by the cationic copolymerization of diglycidyl ether of bisphenol A with ,-caprolactone with an improvement in the shrinkage.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2007Abstract Diglycidyl ether of bisphenol A was cured with different proportions of ,-caprolactone with ytterbium triflate as an initiator. The curing was studied by means of differential scanning calorimetry and Fourier transform infrared in the attenuated total reflection mode. The latter was used to monitor the competitive reactive processes and to quantify the conversions of the epoxide, lactone, and intermediate spiroorthoester groups. A partial depolymerization process from the cured material to free ,-caprolactone was also identified. The formation of a stable carbocation and the coordinative capability of ytterbium triflate were the reasons for this unexpected process. The thermal and dynamic mechanical properties of the cured materials were determined with differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis. An increase in the proportion of ,-caprolactone resulted in an increased curing rate, a decrease in the shrinkage after gelation, and a significant decrease in the glass transition temperature. The introduction of ester linkages into the three-dimensional structure led to more thermally degradable thermosets. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1968,1979, 2007 [source] N,N -dimethylaminopyridine as initiator in the copolymerization of diglycidylether of bisphenol A with six-membered cyclic carbonatesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2006Roser Cervellera Abstract N,N -Dimethylaminopyridine (DMAP) was used as initiator to cure mixtures of diglycidylether of bisphenol A (DGEBA) and 1,3-dioxan-2-one (TMC) or 5,5-dimethyl-1,3-dioxan-2-one (DMTMC). The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated-total-reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing. We observed the formation of five-membered cyclic carbonates and anionic carbonate groups that remain unreacted at the chain ends. The formation of these groups was explained by the attack of the anionic propagation species on the methylene carbon of the carbonate group, which leads to an alkyl-oxygen rupture. By performing the cure in the thermobalance we could evaluate the loss of CO2 produced in the samples containing carbonates. The kinetics were studied by DSC and analyzed with isoconversional procedures. The addition of carbonates slows down the curing rate. Thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) experiments were used to evaluate the properties of the materials obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2873,2882, 2006 [source] Novel Triaromatic Ester Mesogenic Liquid Crystalline Epoxy Resin Containing Both Methyl Substituent and Ethoxy Flexible Spacer: Synthesis and CuringMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2008Guo-dong Liu Abstract A novel triaromatic ester liquid crystalline epoxy resin (LCER) that contains both a methyl substituent and an ethoxy flexible spacer, p -methylphenylene di{4-[(2,3-epoxypropoxy)ethoxy]benzoate} (MPEPEB), has been synthesized. The mesotropic property has been investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (POM). MPEPEB shows a lower melting temperature at 78.7,°C and a broad nematic mesophase temperature range of about 55,°C. Meanwhile MPEPEB shows a mesophase to ,50,°C upon cooling. The curing behavior of MPEPEB with 2,6-diamino-3,5-diethyltoluene (DAE) has been investigated by means of DSC and POM during isothermal and dynamic processes. Although there is little difference between the activation energies obtained from the kinetic data, a marked difference is found between the isothermal and dynamic investigation. The curing reaction in the isothermal investigation roughly obeys n- th order kinetics, while two exothermal peaks appear in the dynamic DSC curves of MPEPEB/DAE. A comparison of the isothermal and dynamic data shows that the curing rate is not a unique function of temperature and curing degree. The cured networks have lower glass temperatures and show a mesophase at room temperature which disappears at about 86,88,°C. [source] Thermal and mechanical properties of a hydroxyl-functional dendritic hyperbranched polymer and trifunctional epoxy resin blendsPOLYMER ENGINEERING & SCIENCE, Issue 10 2001D. Ratna Curing characteristics of blends of a hydroxyl-functionalized dendritic hyperbranched polymer (HBP) and a triglycidyl p-amino phenol (TGAP) epoxy resin have been studied. THe HBP strongly enhances the curing rate owing to the catalytic effect of the hydroxyl groups. THe thermal and dynamic viscoelastic behavior of the blends of various compositions (HBP content 0,20%) have been examined and compared to the neat TGAP matrix. THe glass transition temperature (Tg) gradually decreases with increase in HBP concentration. The blends show a higher impact strength compared to neat TGAP. Scanning electron microscopy analysis indicates a single-phase morphology. [source] Click chemistry in materials synthesis.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007Abstract 1,2,3-Triazole-based polymers generated from the Cu(I)-catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182,5189, 2007 [source] | ||||||||||