The functionalization degree of the resulting PEGDMAs 2k, 4k, 6k, 8k, 10k and 20k was determined to be 70-90% by 1 H NMR spectroscopy (Figure , Figure and Table ). To enable the waterfree DLP printing of "all-PEG" resins, we synthesized a star-shaped PEG-based macrophotoinitiator instead of using conventional hydrophobic (e.g., bisacylphosphine oxide, BAPO, Figure ), or watersoluble photoinitiators (e.g., lithium phenyl-2,4,6-trimethylbenzoyl phosphinate, LAP, Figure ). Bis(mesitoyl)phosphane (BAP-H) group was conjugated to a 4-arm PEG with MW of 10,000 g mol -1 , followed by oxidation of the BAP using a reported route for the synthesis of the linear conjugate (BAPO-PEG-LN, Figures 1d). The structure of the 4-arm macrophotoinitiator BAPO-PEG (Figure ) was confirmed by 1 H and 31 P NMR spectroscopies (Figure ). Under sonication at 70 °C, BAPO-PEG was easily mixed with the semicrystalline macromonomers (Figure ) and a UV absorber (Sudan I, 0.03 wt%) without the need for additional solvents. A customized DLP printer with temperature control of the resin tray and printing head (Figure ), allowed for direct printing of "all-PEG" resins at elevated temperature (e.g., 90 °C). Therefore, the performance of the 3D printed products could be evaluated without the interference of additives, especially the reactive diluents (e.g., N-vinylpyrrolidone (NVP)) that are often used in SLA/DLP to reduce viscosity and dissolve the commercial photoinitiator. To evaluate the 3D printability of the PEG macromonomers, we first measured the viscosity of the polymers between 70 and 100 °C. At 90 °C, the viscosity increased from 10 to 20,000 mPa×s with increasing the PEG MW from 700 to 20,000 g mol -1 (Figure ). The viscosity of PEGDMA 2k-10k was in the printable range of DLP at 70-100 °C, while it would be not possible to print PEGDMA 20k without the addition of diluents. We then printed the PEGDMA 2k-10k resins by heat-assisted DLP using BAPO-PEG as the photoinitiator. The commercial PEGDA 700 was selected as a control. As shown in Figure , all PEG macromonomers showed good printability. Slight deformation was observed due to the re-organization of the PEG chains during the evaporation of the solvent (acetone) used in the cleaning step.