We report a novel semicontinuous method for producing polymer mixtures with tailored molecular weight distributions (MVVDs) and chemical compositions. In contrast to recent methods disclosed for the production of tailored MWDs, the current approach allows the MWD to be tailored at any point in a multistep process. Optimization of a photoflow polymerization process has been performed, where polymer fractions with variable compositions can be produced and independently processed downstream. This independent processing allows complex and tedious operations to be significantly simplified and the polymer structure to be manipulated by varying the production conditions. To illustrate the versatility of our approach, we prepared low dispersity block copolymer mixtures with tailored composition gradients through PET-RAFT polymerization, using a facile one-pass flow technique.