Multifunctional allyl-terminated hyperbranched poly(ethyleneimine) as component of new thiol-ene/thiol-epoxy materials

A new allyl terminated hyperbranched poly(ethyleneimine) was synthesized and characterized and then used in different proportions as multifunctional macromonomer in tetrathiol-diglycidyl ether of bisphenol A formulations. The curing process had a two-stage character and was composed by two click reactions: a first photoinduced thiol-ene addition followed by a thermal thiol-epoxy reaction. The thiol-ene reaction was catalyzed by a radical initiator and the thiol-epoxy curing by tertiary amines. The evolution of the first part of the curing was studied by photo-DSC and FTIR and the results compared with those obtained in a photoirradiation chamber, which was used to prepare samples for thermomechanical tests. These studies showed that the thermal thiol-epoxy process prematurely began during the photoirradiation because the presence of amines in the PEI structure accelerated this process. The thiol-epoxy reaction was more extensively produced when the proportion of the poly(ethyleneimine) increased in the formulation. The overlapping between both processes was greater in the photoirradiation chamber than in the photo-DSC. The intermediate material was completely cured by thermal treatment in an oven. The need of adding 1-methylimidazole as catalyst to complete the thiol-epoxy reaction was derived from the calorimetric studies. The materials prepared were characterized by thermogravimetry and thermomechanical analysis.