Polymerizable plasticizer

Ester plasticizers (phthalates and phosphates) that are used to plasticize PVC (see Chapter 1) are also used as process aids, particularly with NBR and CR. Polymerizable plasticizers such as ethylene glycol dimethacrylate are particularly useful for peroxide curing rubbers. They act as plasticizers or tackifiers during mixing and undergo polymerization by peroxide initiation during cure. 

Esters based on allyl alcohol, such as diallyl phthalate and various polyunsaturated acrylates, have proved useful in improving adhesion of PVC to metal. They may be considered as polymerizable plasticizers. In PVC pastes they can be made to cross-link by the action of peroxides or perbenzoates... 

Polyvinyl Chloride. In plastisol processing, PVC is dispersed in hquid plasticizer then fused to a sol and cooled to a gel to produce rubbery products. When the processor wants to decrease the plastisol viscosity without excessive softening of the final product, he uses a polymerizable plasticizer such as a glycol diacrylate (Fig. 3.71) plus a little peroxide. The plasticizer gives a more fluid plastisol, and then, during hot fusion, the peroxide crosslinks the plasticizer to prevent excessive plasticization of the finished product. 

Typical monomers are of the polymerizable plasticizer type based on functionally active acrylates. A difunctional acrylate (Fig. 12.8) would be used for chain-extension purposes, whilst a trifunctional one (Fig. 12.9) would be primarily used to control crosslink density and hence cure state. Both would have low viscosity, approximately 100 cps, and hence during processing act as plasticizers. 

Diallyl Phthalate n (diallyl o-phthalate, DAP). In the monomeric form, DAP is a colorless liquid ester with a viscosity about equal to that of kerosene, widely used as a crosslinking monomer for unsaturated polyester resins, and as a polymerizable plasticizer for many resins. If polymerizes easily, either gradually or rapidly, increasing in viscosity until it finally becomes a clear, infusible solid. The name DAP is used for both the monomeric and polymeric forms. In the partly polymerized form, DAP is used in the production of thermosetting molding powders, casting resins, and laminates. 

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