Effects of chemistries of trifunctional amines on mechanisms of Michael addition polymerizations with diacrylates

The mechanisms of the Michael addition polymerizations of different trifunctional amines with an equimolar 1,4-butanediol diacrylate (BDA) were investigated by using ¹H and ¹³C NMR to in situ monitor the polymerization processes. The trifunctional amine monomers adopted were 1-(2-aminoethyl)piperazine (AEPZ) and 4-(aminomethyl)piperidine (AMPD) and linear aliphatic amines with different steric hindrance on the 2° amines (original), i.e., N-methylethylenediamine (MEDA), N-ethylethylenediamine (EEDA), and N-Miexylethylenediamine (HEDA). For AEPZ, AMPD, and MEDA with low steric hindrance on the 2° amines (original), the reactivity sequence of the three types of amines was 2° amines (original) > 1° amines ≫ 2° amines (formed) and linear poly(amino ester)s were formed via AB-type intermediates due to the 2° amines (formed) being kept out of the reaction. However, AB-type intermediates were only formed from the 2° amines (original) for AEPZ and AMPD, but from both the 2° amines (original) and 1° amines due to their smaller reactivity difference for MEDA. Nevertheless for EEDA and HEDA, the increased steric hindrance on the 2° amines (original) changed the reactivity sequence of the three types of amines to 1° amines > 2° amines (original) > 2° amines (formed) and branched polymers with degrees of branching of ca. 33% and 37%, respectively, were obtained due to all the three types of amines participating in the reaction. The molecular weights, glass transition temperatures, and thermal stability of the linear or branched poly(amino ester)s obtained were characterized by GPC, DSC, and TGA, respectively.