Reactions in SI-ATRP

In this section, the basic reactions involved in SI-ATRP are discussed, namely initiation, propagation, termination, transfer, equilibrium, and other reactions. Most of the section is further divided on the basis of the curvature of the substrate. 

Surface curvature plays an important role in determining initiation efficiency. The initiation efficiency of SI-ATRP from a flat substrate has been estimated to be around 10% [83-85]. On the other hand, the initiation efficiency that could be obtained from a convex substrate is close to, or even more than, 30% [73-76, 79, 86]. Even higher initiation efficiency values of approximately 80% for particles have also been reported in several studies [77, 78, 87]. In particle systems, some studies have reported a constant increase in initiation efficiency with time [73,75], whereas others reported it to increase as polymerization progresses to higher conversion [77, 78, 86]. This again shows the uncertainty in predicting initiation efficiency. 

Some studies have reported an initiation efficiency of 3-8.5% for concave substrates within ordered mesoporous silica nanoparticles, with mesopore diameter ranging from 1.8 to 2.3 nm [88, 89]. Another study reported 22-37% initiation efficiency when SI-ATRP was conducted in ordered mesoporous silica with 15 nm 

It should be noted that in an experimental setting, the dependence of initiator density on the curvature and the influence of termination reactions may further complicate the actual result. 

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The extent of chain transfer reactions in SI-ATRP could affect the polymerization kinetics and the resulting grafting density of polymers. However, further studies need to be conducted in order to fully understand the role of chain transfer reactions in the SI-ATRP mechanism. 

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