Synthesis of poly-α,α-diphenylglycine. II. Cationic polymerization of 4,4-diphenyl-Δ2-1,2,3-triazolin-5-one

4,4-Diphenyl-Δ²-1,2,3-triazolin-5-one (I) was found to undergo a cationic polymerization under the influence of boron trifluoride etherate in an anhydrous solvent. The poly-α,α-diphenylglycine (III) thus formed contained a larger amount of oligomers than the polymer obtained by thermal decomposition as described in the preceding paper. The molecular weight distribution was further shown to depend on the monomer and catalyst concentration and on the nature of the solvent. A mechanistic rationalization is proposed, involving propagating triazolinium ion pairs (VII) which are not interrupted by chain transfer or termination in the absence of water or alcohol. In the presence of water or alcohol, no polymerization occurred, but the normal acid-catalyzed decomposition products (IV and V) were then obtained. 1-Methyl-4,4-diphenyl-Δ²-1,2,3-triazolin-5-one (VIII) was also treated with BF₃ · OEt₂ in a dry solvent at room temperature and furnished 1-methyl-3-phenyl-indolin-2-one (XII) instead of a polyamide. This reaction constitutes a new method for the synthesis of these heterocycles.