Computer simulations are widely applied to study surface-initiated polymerization (SIP), but in many studies, the chains are assumed to grow at the same speed, implying a homogeneous reaction environment. It has been ignored that SIP is a heterogeneous reaction. A simple stochastic reaction model is proposed in which the heterogeneity of the reaction environment is inherently considered by calculating the reaction probability of each active end individually. It was confirmed that SIP is a heterogeneous reaction, in which the inner chains grow in a monomer-poor region while the outer chains grow in a monomerrich region. The different chain growths lead to a larger dispersity and a broader molecular weight distribution compared with the counterparts of an even chain growth system, which further affects properties like the density profile and the brush height. The results suggest that the heterogeneous reaction environment should be considered, especially when the grafting density is high.

The stochastic reaction model (SRM) treats polymerization as a pure probability‐based issue, which is widely applied to simulate various polymerization processes. However, in many studies, active centers were assumed to react with the same probability, which cannot reflect the heterogeneous reaction microenvironment in heterogeneous polymerizations. Recently, we have proposed a simple SRM, in which the reaction probability of an active center is directly determined by the local reaction microenvironment. In this paper, we compared this simple SRM with other SRMs by examining living polymerizations with randomly dispersed and spatially localized initiators. The results confirmed that the reaction microenvironment plays an important role in heterogeneous polymerizations. This simple SRM provides a good choice to simulate various polymerizations.