n-Butyl isocyanate (nBIC) was polymerized in bulk by the Pruitt-Baggett adduct (PBA) at -23, 0.0, and 25.0-degrees-C. Polymerization was accompanied by trimerization to the cyclic isocyanurates at all temperatures. Spectroscopic evidences supported the nylon-1 structure for both trimer and polymer. The polymer /trimer ratio and the molecular weight of produced polymers were found to increase with decreasing temperature. The Pruitt-Baggett catalyst (PBC), which is the reaction product of (PBA + H2O) system, also polymerized nBIC, but with a relatively slower rate. In aromatic and etheric solutions, nBIC was only trimerized by PBA. Copolymerization of nBIC with propylene oxide by PBA and PBC failed. Some selected monoisocyanates were also polymerized by PBA. (C) 1993 John Wiley & Sons, Inc.