Development of networks in atom transfer radical polymerization of dimethacrylates

The development of networks and structural heterogeneity in the atom transfer radical polymerization (ATRP) of dimethacrylates was studied. The structural and kinetic evolutions during the polymerization were followed using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and extraction/swelling measurement. The reversible activation/deactivation equilibrium between growing radical and dormant species slowed down the polymerization process, giving rise to sufficient chain relaxation and diffusion of reactive species, which favored the formation of homogeneous networks. Compared to the networks prepared by conventional free radical polymerization that favored microgel formation, the ATRP products were more homogeneous, suggested by narrower peak width of the tan δ curve. It was also found that crosslinking density and degree of structural heterogeneity of the ATRP products increased with vinyl conversion. The loss of the living feature at high conversions did not further increase the structural heterogeneity. The ATRP of dimethacrylates with longer spacer yielded more homogeneous networks with lower crosslinking density and lower glass transition temperature.