What Limits the Chain Growth from Flat Surfaces in Surface‐Initiated ATRP: Propagation, Termination or Both?

Surface‐initiated controlled radical polymerization, such as ATRP, has been proven to be a powerful method for preparation of well‐controlled functional grafted polymers. There are thousands of experimental works published, by varying polymers, surfaces, and applications. In comparison, theoretical developments are very lacking. Many fundamental questions still remain to be answered. These questions include, but not limited to: What determine the surface initiator efficiency? How many chains per square nanometer can be fully grown? What is the maximum thickness can polymer grow to? If chains are simultaneously grown from surface and solution, which has higher molecular weight? Answers to these questions are most helpful for innovation and further development in this important area. In this work, we employed recently developed theories to explain experimentally observed kinetic profiles of polymer layer thickness growth. What limits the growth of surface chains? Is it the monomer starvation in grafting layer that slow down propagation? Or is it the termination of radicals that stop the chain growth? It was found that no existing models could fully explain the often contradictory experimental observations. It is our hope that this work will provoke further discussions and inspire more effort in resolving the fundamental issues of this area.