Blue Light Induced Photopolymerization and Cross-Linking Kinetics of Poly(acrylamide) Hydrogels

Blue light induced photopolymerization and photo-cross-linking kinetics of acrylamide (AM), with camphorquinone/diphenyl iodonium hexafluorophosphate (CQ/DPI) as photoinitiators, were investigated. The effects of a number of parameters, including mass fraction of CQ, DPI, and AM (w_CQ, w_DPI, and w_AM) and light intensity (I), on photopolymerization efficiency and photogelation process were systematically studied by photo-differential scanning calorimetry (DSC) and photo-rheometry. Photo-DSC indicated that the maximum photopolymerization rate (R_p, max) was proportional to w_CQ^0.5, w_DPI^0.5, I^0.5, and w_AM, while Photo-Rheometry showed linear relationships between gel time t_gel and w_CQ and I, respectively, and power law relationships between t_gel and w_DPI and w_AM, respectively. In addition, both peak cross-linking rate R_c,max, and delay time t_d, which were both linearly proportional to w_CQ^0.5, w_DPI^0.5, and I^0.5, showed power law relationships with w_AM. Furthermore, exponential patterns were observed between all these factors, w_CQ, w_DPI, w_AM, and I and plateau modulus G'_∞. Combining such correlations obtained from experimental data, an empirical model was established describing the projected mechanical properties of poly(acrylamide) hydrogels from blue light initiated photopolymerization and photo-cross-linking.