Dielectric relaxation spectrum of poly (ε-caprolactone) networks hydrophilized by copolymerization with 2-hydroxyethyl acrylate

The dielectric relaxation spectrum of polycaprolactone (PCL) networks hydrophilized with different amounts of 2-hydroxyethyl acrylate (HEA) is investigated. PCL is a semicrystalline polyester with a complex relaxation spectrum that includes the main α relaxation and two secondary modes (β, γ) at lower temperatures. The overlapping of the different relaxational modes was split by using several Havriliak-Negami functions. Crosslinking the material modifies the dynamics of the main relaxation process as reflected by the parameters that characterize the Vogel behavior of the process and the dynamic fragility. The incorporation of HEA units in the network results in a material with microphase separation: two α processes are detected, the one corresponding to the PCL chains and the new one associated to nanometric regions that contain different amount of both comonomers. The incorporation of the HEA units in the system involves the presence of a new β _sw relaxation due to the link of two side chains by water molecules through hydrogen bonding.