Abstract
The effect of reactive (meth)acrylic cross‐linked polymer microparticles (reactive CPM, also called reactive microgels) used as cross‐linking agents has been studied on the thermo‐mechanical properties of different photopolymerized thin films. The matrix was based on the copolymerization of isobornyl acrylate and ethoxy ethoxy ethyl acrylate or butyl acrylate. Various concentrations of CPM were initially blended with the monomers. These solutions were photopolymerized under UV radiation to obtain hard and transparent films. Since CPM were reactive respect to monomers, they acted as multifunctional cross‐linkers, resulting in networks after polymerization. The well distributed and highly functional CPM which connected acrylate linear chains worked as well defined chemical clusters and gave to the networks a very unique structure. By varying the reactive CPM concentration, the relationship between the number of double bonds introduced into the network by the CPM acting like cross‐linkers and the rubbery modulus of the films was determined from viscoelastic measurements. The structure of CPM, the average functionality and also crystallinity were modified to change networks properties. In addition, reactive groups have been preferentially introduced at the surface vicinity by using a new functional stabilizing agent. CPM were also compared to linear polymers with the same composition. From viscoelastic properties, it is concluded that CPM are very efficient cross‐linkers. However, very high CPM incorporation led to high extent of intramolecular reaction, reducing the cross‐linking efficiency. During thermal aging, CPM and linear copolymer seemed to rearrange leading the film structure to an equilibrium state.
TEM micrograph of a photopolymerized film (30 wt.‐% of CPM‐0% ODA + 70 wt.‐% of IBOA/EEEA) after thermal aging.
magnified imageTEM micrograph of a photopolymerized film (30 wt.‐% of CPM‐0% ODA + 70 wt.‐% of IBOA/EEEA) after thermal aging.