RAFT agent symmetry and the effects on photo-growth behavior in living polymer networks

Abstract

In this work we present a study into the importance of RAFT agent symmetry for photo growth applications based on the one-pot photoexpandable/transformable-polymer networks (PET-PNs) RAFT network. For this we selected an asymmetrical RAFT agent 2-(butylthiocarbonothioylthio) propanoic acid (BTPA) and a symmetrical RAFT agent S,S-dibenzyl trithiocarbonate (DBTTC) to represent these two categories. We prepared 54 parent RAFT network gels. These covered three parameters, including RAFT agent symmetry, monomer to RAFT agent ratio (i.e. RAFT concentration), and crosslinking degree. Subsequently, all of these gels would be grown to give 54 corresponding daughter gels. Additionally, 9 polymer networks based on conventional radical polymerization (FRP) were prepared as controls. In total, 117 polymer networks were studied and compared. We saw the asymmetric RAFT networks undergo a deswelling trend arising from their mesh-filling growth pattern. On the other hand, the symmetric RAFT networks demonstrated a mesh-expansion process, causing them to increase in swelling ratio. These results show the impact of changing a variable as small as the RAFT agent symmetry.