Effect of polymerization temperature and cross-linker concentration on reaction diffusion controlled termination

The effects of temperature and cross-linking agent concentration on reaction diffusion controlled termination have been determined for several loosely cross-linked acrylate and methacrylate systems. The systems studied were 10/90 DEGDA/sBA (10 mol % diethylene glycol diacrylate, 90 mol % sec-butyl acrylate), 1/99/40 DEGDMA/HEMA/PEG400 (1 wt % diethylene glycol dimethacrylate, 99 wt % 2-hydroxyethyl methacrylate diluted with poly(ethylene glycol) 400 to 40 wt %), and 10/90 DEGDMA/ OcMA (10 wt % DEGDMA., 90 wt % n-octyl methacrylate.) The effect of increased cross-linking agent concentration is to decrease the reaction diffusion parameter (R), defined as k(t)/k(p)[M], until a plateau is reached. The reaction diffusion parameter was found to increase as the polymerization temperature is increased above T-g for the methacrylate systems. However, as the temperature is decreased below the T-g for loosely cross-linked systems, R was found to also increase. This phenomenon is not readily predicted using current theory, and thus it is proposed that chain transfer to monomer becomes an important means of radical mobility in loosely cross-linked systems below the T-g. These results enhance the current understanding of reaction diffusion controlled termination, particularly in cross-linked systems.