Ionic (4-allyl)palladium complexes containing bidentate 2,2’-bipyridyl, sparteine and C-2-symmetric bisoxazoline ligands and weakly coordinating anions catalyze the addition polymerization of 3,3-dialkylcyclopropenes. Poly(3,3-dimethylcyclopropene), poly(3-ethyl-3-methylcyclopropene) and poly(3-n-pentyl-3-methylcyclopropene) with molecular weights M-n(GPC) above 10 000 are formed which are nearly exclusively composed of triangular repeating units. In contrast, partial ring-opening occurs during polymerizations with ionic palladium tetrakis(nitrile) complexes [Pd(RCN)(4)][BF4](2) which contain relatively labile nitrile ligands. The latter reactions lead to polymers which contain approximately 50% ring-opened unsaturated repeating units. The polymerizations carried out in the presence of the C-2-symmetric phenyl-substituted bisoxazoline ligand and with the (-)-sparteine-based catalyst lead to partially stereoregular polymers which contain a slight excess of meso units. Assignment of C-13 NMR spectra was aided with a quatercyclopropyl model compound composed of exclusively racemic units. The polycyclopropenes are partially crystalline and show a relatively good short term thermal stability with TGA investigations indicating onset of thermally induced weight loss above 280 degrees C.