The proposal aims at creating a new generic technology to obtain sequence-defined macromolecules by combining advantages of liquid phase synthesis (i.e. fast kinetics, improved yields and selectivities, improved heat and mass transfer, easier upscaling) with advantages of solid-phase synthesis (i.e. fast purification) to produce high-purity oligomers at multi-gram scale without the need for tedious and yield/scope-reducing chemical protection/deprotection steps. Per monomer addition, optimal reaction conditions are created inside the reactor to realize the homogeneous reaction by mixing monomer, solvent, and (co)-catalyst. Key to enable this technology is the selective filtration that takes place after addition of each monomer. Highly stable nanofiltration membranes with optimized molecular weight cut off need to retain the growing macromolecule and remove the remaining monomer and, if applicable, intermediates, catalysts or additives. Each next monomer and its corresponding reaction conditions can then be freely chosen. Based on the complementary expertise of both polymer chemistry groups in thiolactone chemistry, ring-opening of epoxides and conjugated molecules synthesis, respectively, diverse unimers will thus be prepared as proof of principle with also an ultimate material preparation for use in optical computing. All molecular systems pose different requirements on the membranes with respect to stability and selectivity, thus rendering this proposal highly generic.