Both the high Tg and low Tg polymers were able to be dissolved in THF (Figure ), indicating their uncrosslinked nature. With little to no entanglement of the resulting polymers at the high temperatures of FROMP, retention of shape and ability to 3D print these monomers presents a challenge. Therefore, we synthesized crosslinker 6, which consists of two HEN units linked by 1,3-propanediol to add branching or crosslinking to the resulting materials. This design facilitated the copolymerization of monomer 4a with crosslinker 6, enabling the formation of materials via FROMP with improved thermomechanical properties (Figure ). Interestingly, the frontally polymerized materials with varying ratios of crosslinker 6 exhibited similar Tg in both DSC and DMA analyses (Figure ). Only materials with higher concentrations of crosslinker 6 exhibited a rubbery plateau after Tg (Figure ), indicating a higher density of crosslinks. Materials with more than 5 wt% crosslinker exhibited no appreciable dissolution in THF for 48 hours (Table ). We therefore attribute the increasing material elasticity to the enhanced entanglement of branched polymers where the network structure does not span the sample.