Лако-красочные материалы — производство

This effect occurs within systems when there are unreacted monomer molecules in solution. As polymerisation proceeds, the solution becomes progressively more viscous and the movement of all molecules is reduced, with the larger molecules being most affected. Under these conditions propagating radicals can no longer freely contact each other and the rate of termination is […]

Commercial polymerisations usually employ between 0.2-4% of initiator. When the concentration of initiator is reduced, the molecular weight of the polymer is increased, but the conversion of monomer to polymer is reduced. Higher concentrations of initiator form a greater number of polymer chains. These chains are shorter and hence molecular weight and viscosity are lower. […]

Not only does the choice of solvent influence the solution viscosity, but the different degrees of chain transfer activity associated with different solvents affects the molecular weight of the polymer formed. The peroxide initiator reactivity is also influenced by the solvent, the initiator half-life being affected by certain solvents. The boiling point of the solvent […]

Molecular weight is influenced by the monomer concentration. Usually the lower the concentration of monomers the lower the molecular weight of the polymer formed. High concentrations of monomer generate a greater chance that the monomers will come into contact with a propagating chain, and therefore reducing the possibility of chain termination by the solvent or […]

(i) Reaction Temperature Generally the molecular weight of the polymer decreases with increasing temperature of reaction. More initiator molecules are decomposed per unit of time as the temperature is increased. Thus there are more radicals available at any given time and hence more chains are initiated in the presence of the same number of monomer […]

The “Drip-feed” (or continuous addition) process involves feeding monomer and initiator, separately, into solvent at reaction temperature. Ideally, as the monomer and initiator come into contact with the hot solvent, free radicals are formed which immediately initiate polymerisation of the monomer. The polymer formed is dissolved in the solvent and dispersed. In practice, reaction does […]

This technique involves the polymerisation of acrylic monomer in the presence of an organic solvent. If this method is to succeed, both monomer and polymer must be soluble in the chosen solvent. Monomer and initiator are heated in the presence of solvent. The solvent usually comprises 30-40% of the total weight and it may be […]

Acrylic resins for use in industrial surface coating applications are not normally man­ufactured by this technique. However, the high molecular weights that can be obtained, coupled with the freedom of choice of solvent in the application formulation, result in suspension polymerised acrylic resins finding uses in areas such as solvent based inks. The technique is […]

This involves heating monomer mixed with initiator. The problems associated with heat transfer through a viscous reaction mass, result in poor temperature control. This means that long retention times are employed to reduce the chance of localised overheating. Bulk polymerisation can be carried out in disposable containers which are completely filled with the reactants, and […]

Addition polymerisation involves the breaking of a C=C bond and the formation of two C-C bonds. The bond energy for a C=C bond is approximately 100 Kcalories and that for a C-C bond 58.6 Kcalories. The energy balance of the polymerisation can be crudely represented as: (2 x 58.6) -100 = 17.2 Kcalories per mole […]