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This study is the first to employ the use of the copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization to form a tough and stiff, porous material from a well-defined network possessing a high glass transition temperature. The effect of the network linkages formed as a product of the CuAAC reaction, i.e., the triazoles, on the mechanical behavior at high strain was evaluated by comparing the CuAAC foam to an epoxy-amine-based foam, which consisted of monomers with similar backbone structures and mechanical properties (i.e., Tg of 115 °C and a rubbery modulus of 1.0 MPa for the CuAAC foam, Tg of 125 °C and a rubbery modulus of 1.2 MPa for the epoxy-amine foam). When each foam was compressed uniformly to 80% strain at ambient temperature, the epoxy-amine foam was severely damaged after only reaching 70% strain in the first compression cycle with a toughness of 300 MJ/m3. In contrast, the CuAAC foam exhibited pronounced ductile behavior in the glassy state with three times higher toughness of 850 MJ/m3 after the first cycle of compression to 80% strain. Additionally, when the CuAAC foam was heated above Tg after each of five compression cycles to 80% strain at ambient temperature, the foam completely recovered its original shape while exhibiting a gradual decrease in mechanical performance over the multiple compression cycles. The foam demonstrated almost complete shape fixity and recovery ratios even through five successive cycles, indicative of "reversible plasticity", making it highly desirable as a glassy shape memory foams.
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OBJECTIVES: To evaluate "low-shrink" composites in terms of polymerization kinetics, stress development and mechanical properties. METHODS: "Low-shrink" materials (Kalore/KAL, N'Durance/NDUR, and Filtek P90/P90) and one control (Esthet X HD/EHD) were tested. Polymerization stress (PS) was measured using the Instron 5565 tensometer. Volumetric shrinkage (VS) was determined by the ACTA linometer. Elastic modulus (E) and flexural strength (FS) were obtained by a three-point bending test. Degree of conversion (DC) and polymerization rate (Rp) were determined by NIR spectroscopy (6165cm(-1) for dimethacrylates; 4156 and 4071cm(-1) for P90). Photopolymerization was performed at 740mW/cm(2)×27s. Glass transition temperature (Tg), degree of heterogeneity and crosslink density were obtained in a DMA for the fully cured specimens. Analysis of extracts was done by (1)H NMR. Data were analyzed with one-way ANOVA/Tukey's test (α=0.05). RESULTS: The control presented the highest shrinkage and Tg. P90 showed the highest modulus, and NDUR demonstrated the highest conversion. The polymerization rates were comparable for all materials. NDUR and KAL had the highest and the lowest network homogeneity, respectively. The multifunctional P90 had the highest crosslink density, with no difference between other composites. The control had the greatest stress development, similar to NDUR. Crosslinking density and polymer network homogeneity were influenced by degree of conversion and monomer structure. SIGNIFICANCE: Not all "low-shrink" composites reduced polymerization stress. P90 and NDUR had no leachable monomers, which was also a function of high crosslinking (P90) and high conversion (NDUR).
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Resinas Compuestas/química , Materiales Dentales/química , Algoritmos , Reactivos de Enlaces Cruzados/química , Módulo de Elasticidad , Humanos , Curación por Luz de Adhesivos Dentales , Espectroscopía de Resonancia Magnética , Ensayo de Materiales , Metacrilatos/química , Nanocompuestos/química , Docilidad , Polimerizacion , Poliuretanos/química , Resinas de Silorano/química , Espectroscopía Infrarroja Corta , Estrés Mecánico , Propiedades de Superficie , Temperatura de TransiciónRESUMEN
A series of nanogel compositions were prepared from urethane dimethacrylate (UDMA) and isobornyl methacrylate (IBMA) in the presence of a thiol chain transfer agent. The linear oligomer of IBMA was synthesized by a similar solution polymerization technique. The nanogels were prepared with different crosslinker concentrations to achieve varied branching densities and molecular weights. The prepolymers were dispersed in triethylene glycol dimethacrylate at loading levels ranging from 10 wt% to 50 wt%. Photopolymerization reaction kinetics of all prepolymer modified systems were enhanced relative to the nanogel-free control during early stage polymerization while limiting conversion was similar for most samples. Volumetric polymerization shrinkage was reduced proportionally with the prepolymer content while the corresponding decrease in polymerization stress was potentially greater than an additive linear behavior. Flexural strength for inert linear polymer-modified systems decreased significantly with the increase in the prepolymer content; however, with an increase in the crosslinker concentration within the nanogel additives, and an increase in the concentration of residual pendant reactive sites, flexural strength was maintained or improved regardless of the nanogel loading level. This demonstrates that covalent attachment rather than just physical entanglement with the polymer matrix is important for effective polymer mechanical reinforcement by nanogel additives. Reactive nanogel additives can be considered as a practical, generic means to achieve substantial reductions in polymerization shrinkage and shrinkage stress in common polymers.
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OBJECTIVES: This study demonstrates the effects of nano-scale prepolymer particles as additives to model dental monomer and composite formulations. METHODS: Discrete nanogel particles were prepared by solution photopolymerization of isobornyl methacrylate and urethane dimethacrylate in the presence of a chain transfer agent, which also provided a means to attach reactive groups to the prepolymer. Nanogel was added to triethylene glycol dimethacrylate (TEGDMA) in increments between 5 and 40 wt% with resin viscosity, reaction kinetics, shrinkage, mechanical properties, stress and optical properties evaluated. Maximum loading of barium glass filler was determined as a function of nanogel content and composites with varied nanogel content but uniform filler loading were compared in terms of consistency, conversion, shrinkage and mechanical properties. RESULTS: High conversion, high molecular weight internally crosslinked and cyclized nanogel prepolymer was efficiently prepared and redispersed into TEGDMA with an exponential rise in viscosity accompanying nanogel content. Nanogel addition at any level produced no deleterious effects on reaction kinetics, conversion or mechanical properties, as long as reactive nanogels were used. A reduction in polymerization shrinkage and stress was achieved in proportion to nanogel content. Even at high nanogel concentrations, the maximum loading of glass filler was only marginally reduced relative to the control and high strength composite materials with low shrinkage were obtained. SIGNIFICANCE: The use of reactive nanogels offers a versatile platform from which resin and composite handling properties can be adjusted while the polymerization shrinkage and stress development that challenge the adhesive bonding of dental restoratives are controllably reduced.
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Resinas Compuestas/química , Materiales Dentales/química , Metilmetacrilatos/química , Nanopartículas/química , Compuestos de Bario/química , Módulo de Elasticidad , Geles , Humanos , Cinética , Luz , Ensayo de Materiales , Metacrilatos/química , Peso Molecular , Docilidad , Polietilenglicoles/química , Polimerizacion , Ácidos Polimetacrílicos/química , Poliuretanos/química , Refractometría , Silanos/química , Dióxido de Silicio/química , Elastómeros de Silicona/química , Espectroscopía Infrarroja Corta , Estrés Mecánico , Propiedades de Superficie , ViscosidadRESUMEN
OBJECTIVE: Stress development at the tooth/restoration interface is one of the most important reasons for failure of adhesive restorations. The aim of this study was to evaluate the influence of BisGMA/TEGDMA (B/T) and UDMA/TEGDMA (U/T) ratios on polymerization stress (PS) and on the variables related to its development: degree of conversion (DC), polymerization maximum rate (Rp(max)), volumetric shrinkage (VS), elastic modulus (E), stress relaxation (SR) and viscosity of experimental composites. METHOD: Composites were formulated containing B/T or U/T in mol% ratios of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 and 8:2, and 15 wt% of fumed silica. PS was determined with a universal testing machine. VS was measured with a linometer. E and SR were obtained in three-point bending. DC and Rp(max) were determined by real time NIR spectroscopy and viscosity was measured in viscometer. Data were submitted to one-way ANOVA, Tukey test (alpha=0.05%) and regression analyses. RESULTS: PS, VS, E and DC decreased and viscosity and Rp(max) increased with base monomer content in both series. PS showed strong correlation with VS, DC and viscosity. PS, VS and DC were higher and viscosity was lower for UDMA-based materials. SIGNIFICANCE: Reduced viscosity, kinetics parameters and molecular characteristics led UDMA-based composites to elevated conversion and relatively lower PS at lower TEGDMA contents, compared to B/T composites.
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Resinas Compuestas/química , Curación por Luz de Adhesivos Dentales , Análisis de Varianza , Bisfenol A Glicidil Metacrilato , Adaptación Marginal Dental , Análisis del Estrés Dental , Módulo de Elasticidad , Cinética , Ensayo de Materiales , Metacrilatos , Transición de Fase , Polietilenglicoles , Ácidos Polimetacrílicos , Poliuretanos , Análisis de Regresión , ViscosidadRESUMEN
Different monomer structures lead to different physical and mechanical properties for both the monomers and the polymers. The objective of this study was to determine the influence of the bisphenylglycidyl dimethacrylate (BisGMA) concentration (33, 50 or 66 mol%) and the co-monomer content [triethylene glycol dimethacrylate (TEGDMA), ethoxylated bisphenol-A dimethacrylate (BisEMA), or both in equal parts] on viscosity (eta), degree of conversion (DC), and flexural strength (FS). Eta was measured using a viscometer, DC was obtained by Fourier transfer Raman (FT-Raman) spectroscopy, and FS was determined by three-point bending. At 50 and 66% BisGMA, increases in eta were observed following the partial and total substitution of TEGDMA by BisEMA. For 33% BisGMA, eta increased significantly only when no TEGDMA was present. The DC was influenced by BisGMA content and co-monomer type. Mixtures containing 66% BisGMA showed a lower DC compared with mixtures containing other concentrations of BisGMA. The BisEMA mixtures had a lower DC compared with the TEGDMA mixtures. The FS was influenced by co-monomer content only. BisEMA mixtures presented a statistically lower FS, followed by TEGDMA + BisEMA mixtures, and then by TEGDMA mixtures. Partial or total replacement of TEGDMA by BisEMA increased eta, which was associated with the observed decreases in DC and FS. Although the BisGMA content influenced the DC, it did not affect the FS results.
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Bisfenol A Glicidil Metacrilato/química , Resinas Compuestas/química , Materiales Dentales/química , Metacrilatos/química , Polietilenglicoles/química , Ácidos Polimetacrílicos/química , Resinas Compuestas/síntesis química , Materiales Dentales/síntesis química , Módulo de Elasticidad , Análisis de Fourier , Humanos , Ensayo de Materiales , Docilidad , Polímeros/síntesis química , Polímeros/química , Espectrometría Raman , Estrés Mecánico , ViscosidadRESUMEN
OBJECTIVE: To verify the influence of radiant exposure (H) on contraction stress (CS), degree of conversion (DC) and mechanical properties of two restorative composites. METHODS: Filtek Z250 (3M ESPE) and Heliomolar (Ivoclar) were photoactivated with 6, 12, 24, or 36 J/cm2 at continuous irradiance of 600 mW/cm2. CS at 10 min was determined in a low compliance testing system. DC, flexural strength (FS), flexural modulus (FM) and Knoop microhardness (KHN) were measured after 24 h storage at 37 degrees C. KHN and DC measurements were conducted on the irradiated surface of 1mm thick disk-shaped specimens. Bar-shaped specimens were submitted to three-point bending to determine FS and FM. Data were analyzed by one-way ANOVA/Tukey's test (alpha = 0.05) separately for each composite. RESULTS: For Filtek Z250, no significant increase in CS was observed above 12 J/cm2. DC and FM were similar at all H values, while FS increased significantly between 6 and 24 J/cm2. KHN was significantly different among all H levels, except between 12 and 24 J/cm2. For Heliomolar, CS and KHN increased significantly with H, except between 24 and 36 J/cm2. DC, FM and FS did not vary, regardless of the radiant exposure. SIGNIFICANCE: Variables tested behaved differently. CS and KHN were more sensitive to increasing radiant exposures than the other properties evaluated. FS varied only for Filtek Z250, while, for both composites, DC and FM were not affected by different H values.