The B-alkylaminosubstituted borazines (NEt 2) 3 B 3 N 3 H 3 (1), (ΝΕ1 2) 2 (ΝΗΡ0Β 3 Ν 3 Η 3 (2), (NEt 2)(NHPr') 2 B 3 N 3 H 3 (3) and (NMe 2)(NHMe) 2 B 3 N 3 l-l3 (4) have been prepared and characterized by spectroscopic techniques. Their thermolyses at moderate temperature have been investigated in order to elucidate the effects of the nature of the B-alkylamino substituents on the resulting polyborazines backbone. Early stages of the degradations were accompanied by the elimination of primary and secondary amines for (2), (3) and (4). On the basis of 13 C NMR data, oligomerizations have been shown to occur mainly via the formation of direct interring B-N bonds rather than classical deamination with formation of-N(R)-bridges between borazine rings. This phenomenon should be related to the presence of dialkylamino substituents on the boron atoms.