Anionic polymerization of N,N-dimethyl-2-methylene-3-buten-1-amine (5-(N,N-dimethylamino)-isoprene, DMAi) in toluene yields highly regio- and stereoregular polymers. The polymerization proceeds fast compared to non-polar dienes like butadiene or isoprene and polymers with almost exclusive trans-configuration are obtained. The amount of tuans-connected monomer units is found to rise with decreasing polymerization temperature and with increasing molecular weight to a limiting value of about 95% at 25 kg/mol. Kinetic investigations reveal a polymerization behavior which does not follow simple first- or second-order kinetics with respect to monomer concentration. Poly[5-(N,N-dimethylamino)-isoprene] (PDMAi) synthezised in this way is semicrystalline with a degree of crystallinity of 55-60%. It shows a broad melting interval at 70 degrees C besides a glass transition at -30 degrees C. With the help of DSC, WAXS as well as cross-polarized light microscopy, the existence of two different crystal modifications is proven. The observed polymorphism is very similar to the one known from structurally related trans-polyisoprene (TPI).