= Chain-growth initiation
<Chain-growth initiation> creates a chain capable of <chain-growth propagation>. Write
$$
I^*+M\longrightarrow P_1^*.
$$
This schematic includes the first incorporated <monomeric unit>; any preceding production of $I^*$ is a separate step. If $C$ counts <polymer> <molecules>, $A$ counts polymer-bound <polymerization-active sites>, and $S$ counts incorporated <monomeric units>, this event changes $(C,A,S)$ by $(1,1,1)$. The free $I^*$ was excluded from $A$, so this does not assert creation of reactivity from nothing. An initiator feed amount need not equal the number of successful chains: the efficiency of forming productive chains and the number of initiating species per initiator matter. <Organic Chemistry by John McMurry/31.1 Chain-Growth Polymers>[McMurry, §31.1, initiating species and the first reactive intermediate]{ref}
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