Viscoelastic Behavior of Poly(methyl methacrylate) Networks with Different Cross-Linking Degrees

Abstract

The influence of the cross-linking degree on the dynamics of the segmental motions close to the glass transition of poly(methyl methacrylate), PMMA, networks was investigated by three different mechanical spectroscopy techniques: thermally stimulated recovery (TSR), dynamic mechanical analysis (DMA), and creep. The application of the time-temperature superposition principle to isothermal DMA and creep results permitted to successfully construct master curves for PMMA networks with distinct cross-linking degrees. The former results were fitted to the KWW equation. The obtained variation of KWW for the distinct networks indicated that the relaxation curves tend to broaden as the cross-linking degree increases. TSR results clearly revealed a significant shift of the R-relaxation to longer times and a broader relaxation as the cross-linking degree increases, what was also observed by DMA and creep. A change from a Vogel to an Arrhenius behavior was detected by the three techniques with the decrease of temperature below T g. The temperature dependence of the apparent activation energies (Ea) was calculated from DMA, creep, and TSR experiments; above Tg a good agreement was seen between the Ea values for all the techniques. Furthermore, the effect of the cross-linking degree on the fragility of PMMA networks was evaluated. For these materials an increase of fragility with increasing cross-linking degree was observed.

Mechanical, dielectric, and physicochemical properties of impregnating resin based on unsaturated polyesterimides

“…We observe an increase of this modulus on the 4th run of about 5 MPa in a rubbery state. This is directly related to the post-cross-linking phenomenon effect [23]. Indeed, this irreversible phenomenon allows the polymer density to increase and consequently increases its rigidity.…”

“…The analysis of the T gs gives an idea of the methacrylate diluent content. Studies show that the increase in styrene content shifts the T g to a higher temperature and stiffens the UP resin [23]. The use of methacrylate diluent in order to replace styrene seems to be not only for health and environmental interest, but also to reduce the glass transition temperature of the PEI resin.…”

Dynamic mechanical analysis and crystalline analysis of hemp fiber reinforced cellulose filled epoxy composite

“…The width of the relaxation curve is characterized by the β factor of the Kohlrausch-Williams-Watts equation (KWW). A low β value implies a wider distribution, whereas a β value close to the unity means a perfectly narrow relaxation spectrum [49,50] . An increase in free volume usually results in a decrease in the number of cross-linking sites of the polymeric matrix, because there is less cross-linked space between fiber and filler incorporated epoxy matrix.…”

Influence of the Polyhedral Oligomeric Silsesquioxane n-Phenylaminopropyl - POSS in the Thermal Stability and the Glass Transition Temperature of Epoxy Resin

“…In Table 1, the peak height and peak width at halfheight are associated with the homogeneity, i.e., a broader curve can be associated with a greater distribution of relaxation times [15,29] . According to the results, no…”