Viscosity increase during polymerisation

Biesenberg, J. S. etal., J. Polym. Eng. Sci., 1976,16, 101-116 Polymerisation of methyl methacrylate initiated by oxygen or peroxides proceeds with a steady increase in velocity during a variable induction period, at the end of which a violent 90°C exotherm occurs. This was attributed to an increase in chain branching, and not to a decrease in heat transfer arising from the increasing viscosity [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of methyl methacrylate, initiated by azoisobutyronitrile, dibenzoyl peroxide or di-ferf-butyl peroxide [2],... 

After supplying silanol, the heating of apparatus 17 is switched on and the solvent is distilled, sending air through the bubble at the speed of 3 m3/h at 150 °C. The solvent vapours are condensed in cooler 11 and collected in receptacle 18. The distillation of the solvent occurs simultaneously with the condensation of silanol. During the distillation the temperature in apparatus 17 is increased to 170-200 °C, and the speed of air supply is raised to 30 m3/h. The mixture is periodically sampled to determine the viscosity and polymerisation time of the polymer. After the distillation air supply is stopped, the reactor receives a necessaiy amount of the solvent from batch box 10 and the mixture is cooled to 60 °C. The solution (var-... 

The stability improvement of Ti02 suspensions is important not only for water-based paints, but also for paints based on non-polar or low-polar solvents. It is shown in [208] that Ti02 powders modified with an anionic surfactant, e.g. sodium dodecyl sulphate, are dispersed to smaller sizes, and their sedimentation stability increases. The production of water-alkyd emulsions is inhibited due to low mechanical stability. These emulsions can easily break when exposed to shear forces such as those produced by pumps, and when intensively agitated during dispersion. [209] demonstrates that most stable emulsions can be obtained with alkyds showing high acid numbers, as well as with highly polymerised alkyds of low viscosities. 

Figures 15.11(a) and (b) describe the flow and cure of a B-staged aerospace adhesive during a complex thermal history, using parallel plate sensors. Specifically, Figure 15.11(a) shows how the loss factor (log e") changes with time and temperature. The increase in log e" between 25 and 80 °C is due to softening of the adhesive. As the temperature is held isothermally at 80 °C for 30 minutes, log e" remains constant. Then, between 60 and 75 minutes as heat is applied at a rate of 1 °C/min, temperature-induced fluidity causes the viscosity of the resin to decrease. After 75 minutes, the resin polymerises and develops a three-dimensional network, as indicated by the decrease in log e".

As the oil is used, the neutralization number may increase due to contamination (e.g., SO2 from combustion of S in the fuel, CO2 from combustion or that present in atmosphere) and/or oxidation of the oil. The oxidation of the oil results in the formation of oil soluble alcohols, ketones, acids and peroxides (which may polymerise to give insoluble resins) thereby increasing the acid number, viscosity and darkening the oil colour. The rate and extent of oxidation of the oil during use depends on temperature, length of exposure to air or oxygen, amonnt of moisture, catalysts present (formed by the action of oxidation products on the metal surface), type of oil and the inhibitors used. 

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