The tactics of targeting copolymer composition (CC) and molecular weight (MW) via semibatch controlled radical polymerization (CRP) have been extensively studied. However, little effort is made to target copolymer sequence length (CSL) and its triad sequence, which are among the key microstructures determining material properties of the copolymers. This work presents a method to design and synthesize targeted CSL and copolymer triads in a reversible addition-fragmentation chain transfer radical mini-emulsion copolymerization system (RAFT) through a semibatch chain and sequence model coupled with Alfrey Mayo model. The kinetic model was first derived and correlated with experimental results of the batch St/BA copolymerizations. The semibatch RAFT model was then employed to calculate the feed-rate to target CSL and their triads. St/BA copolymers with different uniform CSLs and their triads are synthesized through the programmed semibatch RAFT mini-emulsion copolymerization processes.