Mechanism of UV‐Induced Gelation of Acryloyl‐Type Monomer and Polymer Solutions Using Persulfate as Photoinitiator

An aqueous solution containing acryloyl-type monomers or polymers undergoes gelation by UV irradiation in the presence of APS as UV-photoinitiator. We investigate the mechanism of the UV-induced gelation using LS and ESR. In LS, the dependence of the gelation time t gelation on the APS concentration CAPS is demonstrated for NIPAm solutions, and the relation between CAPS and t gelation fits a power law function, i.e., t gelation ∼ C APS -1/2 , indicating that UV-induced gelation progresses according to a radical polymerization mechanism. On the other hand, ESR data reveal that the UV-induced cross-linking reaction takes place at α-carbon atoms in acryloyl-type monomers and polymers.