HEA polymerization in the bulk phase. 1, 2.5, and 5 wt% LAP stock solutions were prepared in water. The monomer to initiator weight ratio (HEA/LAP) was varied from 200/1, 10/1, up to 5/1 by pipetting different amounts of the LAP solutions on top of the bulk phase. The samples were left in the dark for equilibration for at least 48h and then irradiated with UV light (Superfire S11-H 360 nm, Shenzhen, China) for 2 h.