An exhaustive study of chain-length-dependent and diffusion-controlled free radical and atom-transfer radical polymerization of styrene

A finely tuned-up and high-performance Monte Carlo simulation, which takes diffusion-controlled and chain-length-dependent bimolecular termination reactions into account, is developed to thoroughly simulate and compare free radical (FRP) and atom transfer radical polymerization (ATRP) of styrene. It is found out that the termination rate constant falls and eventually plateaus upon the increase of the chain length of radicals. In addition, average termination rate constant greatly decreases during ATRP; nonetheless, it remains almost unchanged and smaller in FRP. Moreover, there is an accumulation of CuBr₂ in the reactor as the ATRP proceeds, while the concentration of CuBr decreases and finally plateaus. Polymer chains are entirely initiated at the beginning of the ATRP, whereas initiation of chains continues throughout the free radical polymerization up to the end of the reaction. Also, the dead polymers are much lower in concentration (only 20%) in ATRP as compared to FRP (about 50%). In addition, a shift (toward higher molecular weight) in the location of the peaks of molecular weight distributions can easily be seen for the ATRP system, whilst the chain length distribution of free-radically generated polymers remains the same throughout the free radical polymerization. The molecular weight distributions narrow as the atom transfer radical polymerization progresses. Finally, the simulation results correspond closely to the experimental data.