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

The effects of temperature and cross-linking agent concentration on reactio n diffusion controlled termination have been determined for several loosely cross-linked acrylate and methacrylate systems. The systems studied were 1 0/90 DEGDA/sBA (10 mol % diethylene glycol diacrylate, 90 mol % sec-butyl a crylate), 1/99/40 DEGDMA/HEMA/PEG400 (1 wt % diethylene glycol dimethacryla te, 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 m ethacrylate.) 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 i ncrease as the polymerization temperature is increased above T-g for the me thacrylate systems. However, as the temperature is decreased below the T-g for loosely cross-linked systems, R was found to also increase. This phenom enon is not readily predicted using current theory, and thus it is proposed that chain transfer to monomer becomes an important means of radical mobil ity in loosely cross-linked systems below the T-g. These results enhance th e current understanding of reaction diffusion controlled termination, parti cularly in cross-linked systems.