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

Photopolymers serve as basis for stereolithography, an additive manufacturing process which gains increasing attention due to its high throughput and exceptional spatial resolution. Photopolymers provide high stiffness, strength and heat deflection temperature, but they frequently lack toughness which limits their field of application. A deeper understanding of the structure-property relations is therefore important in order to develop photopolymers with improved thermomechanical properties.
The properties of photopolymers strongly depend on the constitution of the network that is formed during polymerization. While, for example, highly reactive multi-functional monomers induce crosslinks and therefore increase the rigidity of the material, they also influence the polymerization process itself and the overall conversion. Hence, it is not clear, a priori, what the resulting polymer network looks like.
In this work a modified version of “Polymatic” is used to simulate the polymerization of photocurable (meth)acrylate materials. Such molecular dynamics simulations allow to follow the reaction step by step and the distribution of soft and hard segments can be determined. This reveals important information about the polymer network that otherwise would not be accessible. Also, the relation between initiator concentration and the conversion of different species can be investigated. Another aspect is the arrangement of high molecular weight molecules inside of a crosslinked matrix. Mixing long molecules with short molecules is done to increase the toughness of photopolymers, but experiments have shown that the efficacy of this approach likely depends on the network structure.
Recent research suggests that the homogeneity of the polymer network plays an important role. The presented simulations are a tool to investigate network homogeneity and can help exploring the limitations of chain growth polymerization in this regard.
Further generalization of the presented method will help explore the network structure of step growth polymerized polymers which are known to form more homogenous networks.