EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In this work, the development of phase separation in the photopolymerization of a (meth)acrylate system based on the thermodynamic instability of components has been addressed. Heterogeneous (meth)acrylates could lead to photopolymers in dental materials with improved thermomechanical properties. While incorporating components with different properties into an integrated polymer is a common way to make use of their advantageous potential, improving the fracture toughness of photopolymers was shown to be highly dependent on the formation of certain degrees of phase separation. Since several parameters are required to establish phase separation and hence the characteristics of the resulted polymer, it is essential to have a clear understanding of the morphology of the phases created during the process. However, due to the amorphous structure as well as the very high rate of (meth)acrylates curing followed by the formation of heterogeneous polymer architecture, conventional light microscopic methods can commonly not confirm the development of individual phases. Therefore, by considering the diversity of the chemical structure of (meth)acrylates, a susceptible system to phase separation consists of a urethane acrylate oligomer and a dimethacrylate monomer was implemented. Atomic force microscopy imaging was employed to observe phase separation in both contact and AC mode. The findings revealed that AC mode provides results that can better reflect the differentiation of phases based on the hardness of the phases developed. It was found that oxygen could adversely affect the progress of the reaction as well as the development of phase separation on the surface by interacting with the active radicals and needs to be avoided. Furthermore, it was shown that the distribution of soft phases within the hard phase has an extraordinary impact on the fracture toughness of the final polymer.

KEYWORDS: phase separation, Photopolymerization, (Meth)acrylate resins, Atomic Force Microscopy