We report the synthesis by the reversible addition-fragmentation chain transfer process of well-defined decablock polymers with a final dispersity as low as 1.15 and a fraction of living chain as high as 97% after 10 successful block extensions, each taken to >99% monomer conversion. By using model decablock homopolymers of poly(N,N-dimethylacrylamide) and poly(4-acryloylmorpholine) of relatively low DP (10 units per block in average), we describe the theoretical and experimental considerations required to access high-order multiblock copolymers with excellent control over molecular weight distributions and high livingness.