Herein, the synthesis of polyethylene via an innovative post-polymerization modification (PPM) approach is reported. For this, a block copolymer of poly[N-(acryloyloxy)phthalimide] (PAP) is synthesized by straightforward reversible addition-fragmentation chain-transfer (RAFT) polymerization using a dedicated macroRAFT transfer agent. Upon decarboxylation of the PAP block, followed by efficient block copolymer cleavage, a polyethylene homopolymer with a predictable degree of polymerization is obtained.