Photopolymerized　hydrogels　are　critical　to　soft　devices,　mechanobiology,　regenerative　medicine,　and　next　generation　drug　delivery.　However,　the　optimization　of　processing　protocols　for　all　of　these　applications　of　photopolymerized　hydrogels　has　been　at　least　semi-empirical　due　to　the　lack　of　a　comprehensive　predictive　framework.　Herein,　we　developed　the　first　comprehensive　predictive　framework　for　how　the　chemical　kinetics,　optical　properties,　and　mechanical　properties　of　a　photopolymerized　hydrogel　emerge　from　a　precursor　solution　as　the　solution　is　illuminated,　and　of　how　these　processing　parameters　relate　to　the　final　mechanics　of　the　hydrogel.　We　validated　the　model　experimentally　using　an　eosin　Y-initiated　di-acrylate　system.　The　model　revealed　that　processing　kinetics　were　dominated　by　photobleaching　and　crosslinking,　and　that　network　mechanics　were　dominated　by　chain　growth　and　loop　formation.　We　demonstrated　the　utility　of　the　model　by　using　it　to　design　and　then　synthesize　hydrogels　with　specified　gradients　in　mechanical　properties.　The　modeling　framework　is　general　and　enables　design　of　a　broad　range　of　hydrogels.　©　2020　Elsevier　Ltd