Anionic ring-opening polymerization of propylene oxide in the presence of potassium alcoholate initiator was accelerated by addition of the bulky phosphonium salt tetrakis[cyclohexyl(methyl)amino]phosphonium-tetrafluoroborate. Dipropylene glycol (DPG) was partially deprotonated (5%) and used as an initiator for the polymerization performed at 100 degreesC at normal pressure. The delocalization of the positive charge over five atoms promoted the formation of a separated ion pair, thus enhancing nucleophilicity and reactivity. Compared with those of polyaminophosphazenes and tetrabutylphosphonium cation, the average propagation rates increased in the order of Bu4P+, K+, P-1(+), P-2(+), and (BuP4H+)-Bu-t. DPn for the polymers was in the range of 20-64. Characterization of poly(propylene oxide)s by means of H-1 NMR, size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) showed low polydispersities (M-w/M-n) without any byproducts or impurities. The M-w/M-n obtained was 1.03-1.09 (MALDI-TOF-MS) and 1.11-1.15 (SEC), respectively. Values calculated from titration of the hydroxyl groups showed good agreement. Determination of the total degree of unsaturation in the range of 13-60 mmol/kg indicated larger amounts with increasing polymerization rates.