Photopolymerization Kinetics of Different Chain Sizes of Bi-functional Acrylic Monomers using Real Time FT-IR

In this study, the photopolymerization kinetics of bifunctional acrylic monomers having different chain lengths, such as 1,4-bis(acryloyloxy)butane, 1,6-bis(acryloyloxy)hexane, and 1,10-bis(acryloyloxy)decane, was investigated by real-time Fourier transform infrared (FT-IR) spectroscopy, using Irgacure 184 (R) (1 wt%) as the photoinitiator. Dark polymerization analysis was employed for measuring the kinetic constants for propagation and termination. Plots of kinetic constants for propagation against double-bond conversion showed a plateau, suggesting that the reaction rate is controlled at low conversion, and with increasing conversion, the reaction rate decreases as the diffusion rate of the monomer controls propagation. At low conversion, as compared to the reaction for a monomer having a long chain length, the propagation reaction for a monomer with a short chain length switched to a diffusion-rate controlled propagation reaction. The results suggested that short chain length monomers form a dense cross-linking network, which hinders the diffusion of the monomer, and the kinetic constants decrease at low conversion. The results obtained from the plot of kinetic chain length versus conversion indicated that at a maximum kinetic chain length of up to 106, the reaction switches to the diffusion-rate controlled propagation of each monomer.