Poly(phosphoester)s (PPEs) are interesting degradable multi-functional polymers. Here, we present the first synthesis of poly(phosphoramidate)s (PPAs) via acyclic diene metathesis (ADMET) polycondensation with amidate linkages in side chains. In contrast to conventional polyamides, the P-N-bond in phosphoramidates is more labile than the corresponding esters. Unsaturated PPAs were compared with structural analogues of PPEs: two novel α,ω-dienes, i.e. bis-(undecen-10-yl)-n-butyl-phosphoramidate (1) and bis-(undecen-10-yl)-n-butyl-phosphate (2) have been polymerized by Grubbs-type catalysts to polymers with molecular weights up to ca. 20 000 g mol-1. After hydrogenation polyethylene-like structures were obtained with the phosphoramidate or -ester representing a precisely placed defect. PPAs were compared to their PPE analogues with respect to their thermal behavior and stability by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), showing similar crystallization behavior for the saturated materials, but significant differences for unsaturated PPA vs. PPE. This synthesis of PPAs via ADMET polymerization offers an interesting approach to various PPAs. The hydrolytically labile pendant phosphoramidate further offers the possibility for the development of hydrolytically degradable materials or as processable intermediates for poly(phosphodiester)s which often show limited solubility.