10-Undecenal, derived by pyrolysis and reduction from castor oil, was almost quantitatively transformed into the corresponding aldol condensation product under basic conditions. This α,ω-diene monomer was polymerized using acyclic diene metathesis (ADMET) polymerization. In a catalyst screening, four of nine different ruthenium-based metathesis catalysts showed good reactivity under neat conditions at 80°C in the presence of 1,4-benzoquinone and polymers with molecular weights up to 11 kDa were formed. Furthermore, the 1H NMR spectra showed that the metathesis catalysts tolerate the α,β-unsaturated aldehyde function and due to the addition of benzoquinone, the degree of double bond isomerization was low. Further experiments investigating reduced catalyst amounts (down to 0.2 mol%) and the temperature dependence of these ADMET polymerizations gave also satisfying results for the formation of poly-α,β-unsaturated aldehydes. Moreover, ADMET polymerizations with different amounts of methyl 10-undecenoate as chain-stopper were performed and the integrals of the corresponding 1H NMR spectra allowed the determination of an absolute degree of polymerization. Finally, a reduction of a poly-α,β-unsaturated aldehyde with sodium borohydride was accomplished. The resulting poly-(allyl alcohol) could be a useful compound in the generation of polymer networks like polyesters, polyurethanes, and polycarbonates and thus be of high interest in materials research.