Chain transfer polymerization agents Chloroprene

A method for the controlled emulsion polymerization of chloroprene using dithiocarbamic esters as sulfur-based chain transfer agents is described. The method provides industrially relevant molar masses with Mn s> 50,000 daltons with good yields in acceptable times. It was further determined that when pKa values for the dithiocarbamic acid precursors were less than 12, the thioester was ineffective as a regulator. 

TABLE 1. Effect on the polymerization of chloroprene nsing selected dithiocarbamic esters as sulfnr-based chain transfer agents. 

The polymer which is obtained when chloroprene is emulsion-polymerized in the absence of sulfur or a chain-transfer agent is a tough, insoluble non-plastic material. If sulfur is dissolved in the chloroprene prior to polymerization (at a level of 0.5-1.5 parts by mass per 100 parts by mass of monomer), the product is still a tough insoluble material which is unsuitable for use as an elastomer. However, by heating the latex obtained (still in an alkaline condition) with a thiophilic reagent, such as tetraethylthiuram disulphide (Vlll), the polymer becomes plasticized or peptized to a soft, plastic, soluble polychloroprene which is suitable for use as an elastomer. 

Properties Water-wh. to pale yel. liq. sol. in ether, alcohol insol. in water m.w. 202.44 dens. 0.849 (15.5/15.5 C) m.p. -7 C b.p. 274-278 C flash pt. (OC) 127 C ref. index 1.4589 Toxicology Irritant avoid contact and inh. strong sensitizer mutagenic data TSCA listed Precaution Combustible Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of SOx Uses Catalyst accelerator for unsat. polyester resins modifier in polymerization reactions, esp. for SBR reducing initiator chain transfer agent for styrene-butadiene/chloroprene rubber prod. In food-pkg. adhesives adjuvant in food pkg. 

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