Harnessing light to create functional, three-dimensional polymeric materials: multitasking initiation systems as the critical key to success

Nowadays, the lack of suitable photoinitiators (PI) and photoinitiating systems (PISs) represents the utmost challenge in 3D-VAT printing. High photoinitiating efficiency is needed for example in the presence of nanofillers such as carbon nanotubes (CNTs) which absorb and scatter light. Many prominent PISs contains iodonium salt as an initiator and a second component as a photosensitizer. This study addresses the high demand for innovative PISs with improved photoinitiating efficiency by a complete cycle of research: from the synthesis of new biphenyl derivatives, through their employment as photosensitizers of iodonium salt for light-induced cationic, free-radical, and hybrid polymerization processes, to the representative application in 3D printing processes such as digital light processing (DLP) or laser printing. The ultimate performance of the newly synthetized compounds was tested by preparing 3D-printable photosensitive nanocomposite resins filled with CNTs as a nanoscale filler. Their photopolymerization kinetics as well as the effect of the CNT concentration on the crosslinking were analyzed via real-time FTIR and photo-rheology. The printouts were observed with optical microscopy and scanning electron microscopy. In addition, the key printing parameters were determined, i.e. Ec (critical energy to initiate polymerization) and Dp (penetration depth of curing light). Our results evidence the capability of the synthetized compounds to take part in the photoinitiating systems of complex and demanding 3D printing applications