PURPOSE: To produce chloroprene rubber controlled in a decrease in Tg, improved in crystallization resistance and having good low-temperature properties, by copolymerizing dichlorobutadiene with chloroprene in a specified manner.
CONSTITUTION: A mixture of 0.7W6mol% 2,3-dichlorobutadiene-1,3(2,3-DCB) and 94W99.3mol% 2-chlorobutadiene-1,3(chloroprene) is emulsified and, a catalyst such as potassium persulfate, is added thereto to start polymerization at about 10W60°C. At the same time, the polymerization is continued while 2,3-DCB is fed to the polymerization system at a rate of ACx/tmol per min per 100mol of the entire monomer [wherein A is 0.015W0.019, C is a conversion (%) when the polymerization is terminated, x is an amount (mol%) of 2,3-DCB in the monomer mixture initially emulsified, and t is a polymerization time (min)]. When the conversion reaches 60W80%, the addition of 2,3-DCB an the polymerization reaction are terminated form a chloroprene copolmer containing 2W15mol% 2,3- DCB.
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