Semicrystalline aliphatic polyphosphoesters can be obtained in a one-step approach by polyesterification of readily available bio-based long-chain diols with dichlorophosphorus compounds. Nonadecane-1,19-diol and tricosane-1,23-diol with respectively methylphosphonic dichloride or phenyl dichlorophosphate yield polymers (PPE19Me, PPE23Me, PPE19(OPh), and PPE23(OPh)) with molecular weights M-n up to 3 X 10(4) g mol(-1). DSC analysis of these polymers and a C-12 analogue reveal significantly enhanced crystallinities and melting points (up to T-m = 87 degrees C) with increasing methylene sequence length. DMA on injection-molded samples shows glass transitions at -19 degrees C (PPE19Me) and -12 degrees C (PPE23Me). Single crystals of PPE19Me accommodate a single C-19 repeat unit, as concluded from a lamella thickness of only 3 fun thick determined by AFM. Hydrolytic degradation of solid polymer samples under ambient conditions occurred only to a minimal extent over three months by hydrolysis of very small amounts of in-chain anhydride defects.