Astramol polypropyleneimine dendrimers as Norrish type II amine synergists

Amine synergists as part of a Norrish Type II photoinitiating system are widely employed in UV-curable coatings for various applications. In most of these applications they serve a dual role ie as initiator and as oxygen scavenger. Dimethylethanolamine is one of the more frequently employed aliphatic amines. However, this amine is a highly volatile. Astramol™ polypropyleneimine dendrimers have a very low volatility and are employed succesfully as aliphatic amine synergists in UV-curable products. RT-FTIR measurements have demonstrated that in air these dendrimers are better initiators for acrylate polymerisation than dimethylethanolamine under nitrogen employing benzophenone as sensitiser. These low volatile aliphatic dendrimers in combination with isopropyl thioxanthone can initiate the acrylate polymerisation under nitrogen faster than the well known combination in which octyl dimethylamine benzoate serves as a low volatile aromatic amine synergist. Based on extraction studies it has been shown that, especially when using the nitrile content terminated Astramol™ dendrimers, these multifunctional amine synergists can not be extracted from a coating.