Monitoring of the Gelation Process on a Radical Chain Cross‐Linking Reaction Based onN‐Vinylcaprolactam by Using Dynamic Light Scattering

Summary:The sol‐gel transition of radical chain cross‐linking copolymerization system [N‐vinylcaprolactam (monomer)/3,3′‐(ethane‐1,1‐diyl)bis(1‐vinyl‐2‐pyrrolidone) (cross‐linker)] has been studied using in situ by time‐resolved dynamic light scattering (DLS). A critical dynamical behavior was observed near the sol‐gel transition, which is characterized by the presence of power‐law spectra over three decades in the time‐intensity correlation functiong2(t) − 1 ∼ t−μ. It was found, that the critical exponentμis dependent on the amount of the cross‐linker: higher the amount of the cross‐linker, higher is the value of the exponentμ. The occurrence of speckle patterns in the scattered intensity profile and of a power law behavior in the time‐intensity correlation function appeared at the same time. At the lowest concentration of 0.25% cross‐linker, no power law was observed. The estimated values forμwere in the range of 0.39 ≤ μ ≤ 0.577. It can be concluded, that the amount of branching in the critical gel determines the value ofμ. magnified image