Improved 2PP additive manufacturing build/process quality via the use of hyperbranched pre-polymer

This study reports the first systematic study investigating the potential of using hyperbranched (HB) polymers as novel materials for improving two photon polymerisation (2PP) processing. It demonstrated that HB polymer containing additive manufacturing resins can be successfully formulated and used to print: (a) mono-/multi-material structures, the latter containing monomers of different functionality (i.e., hydrophilic/hydrophobic mixes), (b) with a broader range of printing conditions, (c) to high levels of cure and (d) at faster processing speeds than monomeric resins. A printed multi-material structure was confirmed to contain both feed materials and exhibit high cure by ToF-SIMS and Raman analysis, respectively. Thus, HB polymers were shown to improve mixing in multi-functional resins and overcome 2PP chemistry restrictions. When processing with selected HB polymers, both the polymerisation "onset" and "burning" thresholds were improved compared to monomeric resins. Processing more reactive HB polymers still increased the overall processing window compared to the 2PP processing of the equivalent monomer, but the "burning" threshold was in fact lowered, which was linked to depolymerisation events. Thus, a HB polymer was subject to degradation studies and shown to produced more residual material (i.e. "char") than linear materials, which delivers the decolourisation in 2PP "burning". This study confirms that using HB polymers can extend the viability and utility of 2PP processing, improvements that were delivered by understanding the reactivity of these pre-polymers toward both polymerisation and depolymerisation.