Influence of solvent on the network structure formed by free radical polymerization of tri-ethylene glycol dimethacrylate: A dielectric study

Molecular mobility of a series of tri-ethylene glycol dimethacrylate (TrEGDMA) samples polymerized with different amounts of ethyl acetate up to 40% (w/w) as diluent was investigated by dielectric relaxation spectroscopy. In the first measuring scan, the samples show three secondary relaxation processes: a γ process related to the twisting motions within the ethylene glycol moiety as found in the unreacted monomer, a β process assigned to hindered rotations of carboxylic groups residing in non-bonded ends of the monomers linked to the network only by one side of the molecule; and additionally, at higher temperatures, a third process was detected designated as βpol, ascribed to a π flip of the ester unit accompanied by a restricted main chain rearrangement. While the γ and the βpol processes remain in the second scan, the β relaxation goes to extinction due to post-polymerization that took place at the highest temperatures scanned in the previous run, leading to complete polymerization of the network. The strength of γ and β relaxation measured in the first scan increases with the amount of solvent present in the initial mixture, nevertheless, in any case, β relaxation completely disappears in the second scan.