高分子化学课件课件.ppt

ACS Macro Letters * Solution Polymerization Heat removed during polymerization can be facilitated by conducting the polymerization in an organic solvent or water Solution Polymerization Solvent Requirements: Both the initiator and the monomer be soluble in it The solvent have acceptable chain transfer characteristics and suitable melting and boiling points for the conditions of the polymerization and subsequent solvent-removal step. Solution Polymerization Solvent choice may be influenced by other factors such as flash point, cost and toxicity Reactors are usually stainless steel or glass lined Solution Polymerization Disadvantages: small yield per reactor volume The requirements for a separate solvent recovery step Suspension Polymerization Definition: A polymerization process in which the monomer, or mixture of monomers, is dispersed by mechanical agitation in a liquid phase, usually water, in which the monomer droplets are polymerized while they are dispersed by continuous agitation. Used primarily for PVC polymerization Suspension Polymerization If the monomer is insoluble in water, bulk polymerization can be carried out in suspended droplets, i.e., monomer is mechanically dispersed. The water phase becomes the heat transfer medium. Suspension Polymerization So the heat transfer is very good. In this system, the monomer must be either 1) insoluble in water or 2) only slightly soluble in water, so that when it polymerizes it becomes insoluble in water. Suspension Polymerization The behavior inside the droplets is very much like the behavior of bulk polymerization Since the droplets are only 10 to 1000 microns in diameter, more rapid reaction rates can be tolerated (than would be the case for bulk polymerization) without boiling the monomer. Emulsion Polymerization Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. Emulsion Polymerization The most common type o