Effect of Azo and Peroxide Initiators on a Kinetic Study of Methyl Methacrylate Free Radical Polymerization by DSC

MMA-based fast-curing repair materials suitable for low-temperature application

In this study, the application of methyl methacrylate (MMA) resin as the binder and standard sand as the aggregate has been employed to prepare the repair materials that can be cured in the sub-zero temperature environment. For this purpose, the redox initiation system of benzoyl peroxide (BPO) and N,N-dimethyl-p-toluidine (DMPT) has been used. Subsequently, the influence of initiator and accelerator content on the compressive strength, flexural strength, curing time and other properties of the materials has been revealed. At an ambient temperature of 0 °C, with BPO = 4.5% and DMPT = 3.5%, the developed repair materials can be cured within 31 min, and the 1 h compressive strength reaches 84.6 MPa. At an ambient temperature of −25 °C, with BPO = 4% and DMPT = 5%, the repair materials can be cured within 43 min, with the 1 h compressive strength reaching 53.4 MPa. The materials can be swiftly cured at low-temperature and exhibit excellent mechanical properties, thus, confirming their suitability for extreme environments. Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and other techniques have been employed to characterize the developed materials.

Self-Initiated Butyl Acrylate Polymerizations in Bulk and in Solution Monitored By In-Line Techniques

High-temperature acrylate polymerizations are technically relevant, but yet not fully understood. In particular the mechanism and the kinetics of the thermal self-initiation is a topic of current research. To obtain more detailed information the conversion dependence of the polymerization rate, r_br, is determined via in-line DSC and FT-NIR spectroscopy for reactions in bulk and in solution at temperatures ranging from 80 to 160 °C. Solution polymerizations revealed that dioxane is associated with the highest r_br, while aromatic solvents result in the lowest values of r_br. Interestingly, r_br for polymerizations in solution with dioxane depends on the actual monomer concentration at a given time in the system, but is not depending on the initial monomer concentration. The overall rate of polymerization in bulk and in solution is well represented by an equation with three or four parameters, respectively, being estimated by multiple linear regression and the temperature as additional parameter.

The effect of initiator encapsulation on methyl methacrylate polymerization by isothermal differential scanning calorimetry

Microcapsules containing initiator of cumene hydroperoxide or tert-butyl peroxy-2-ethylhexanoate as core material and polyurea as shell material were prepared by condensation polymerisation in oil-in-water emulsion at different agitation speeds. And their effects on the polymerisation of methyl methacrylate were investigated by isothermal differential scanning calorimetry. In comparison to unencapsulated initiators, the use of encapsulated initiators significantly delayed the reaction, reduced the maximum heat flow, relatively reduced the maximum reaction rate, and made the conversion smaller. In addition, the encapsulated initiator shortened the time lag, increased the heat flow at the maximum point as the reaction temperature increased, and further delayed the appearance time of the maximum reaction point as the agitation speed decreased. The theoretical values calculated by the modified Kamal model, including the nth-order reaction formula and the autoacceleration reaction, were in good agreement with our experimental data. We observed the more prominent autoacceleration reaction at a higher conversion.