It is well-known that controlled/living radical copolymerization (CLRcoP) yields gradient copolymer with the composition varying along chain length. The composition distribution of the as-synthesized product is solely determined by the comonomer reactivity ratios and is thus not well controlled. This work reports the first experimental example of the control over the copolymer composition distribution through semibatch operations. Using styrene (St)/butyl acrylate (BA) as a model system, we synthesized uniform and linear gradient copolymers via semibatch reverse addition-fragmentation chain transfer radical polymerization (RAFT) mediated by benzyl dithioisobutyrate. The comonomer feeding rate profiles for the targeted distributions were designed from a newly developed computer model that was trained from the batch RAFT copolymerizations of St and BA at different monomer compositions. The semibatch copolymerization yielded precise copolymer products having their composition distributions exactly as targeted and the polymerization rate and molecular weight profiles as predicted by the model.

Summary: Although controlled/living radical copolymerization has been extensively studied, the control of copolymer composition distribution receives little attention. In this paper, taking RAFT copolymerization as an example, we develop a mathematical model and simulate copolymerization systems with various reactivity ratios. It is demonstrated that through semi‐batch operations with programmed profiles of slow monomer feeding rate, precise control over copolymer composition distribution (uniform and designed gradient distributions) along polymer chain can be achieved. It is also found that the semi‐batch operations have lower rates of polymerization than their batch counterparts. The reason for this difference is analyzed, and the magnitude depends on the reactivity ratios and targeted copolymer composition. The improvement of the semi‐batch rate by distributing a part of the initiator amount to the monomer feeding tank is found to be minor.

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