AbstractAn analysis is given of the effect of reactor design on the variation of composition and extent of blocking in anionic copolymerization. Batch, pipeline, continuous stirred tank (CSTR), and recycle reactors are contrasted. Specifically, alkyl lithium‐polymerized butadiene–styrene and alkyl sodium‐polymerizedp‐methylstyrene–styrene are contrasted to the products of copolymerization of the same monomers by free‐radical mechanism. It is shown for both systems that considerably more extensive blocking occurs in a batch reactor when the anionic polymerization mechanism is used. The free‐radical copolymers, unlike the anionic copolymers, exhibit compositional heterogeneity in a batch reactor. Carrying out the polymerization reaction in a pipeline reactor gives results equivalent to the batch reactor if there is plug flow. However, if a parabolic profile exists in the reactor, there will be significantly increased compositional drift in the copolymer product and a broadened molecular weight distribution, with little effect on blocking. Recycle reactors, including the recirculating loop variety, seem effective in decreasing blocking. The extent of blocking may be considerably decreased in a wellmixed continuous stirred tank reactor. However, poor mixing will greatly increase both the extent of blocking and the compositional heterogeneity o
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