Figure shows three principal MW-dependent reaction domains: PEGs with high MW -highlighted for the exemplary PEG with MW of 6380 Da as blue vertical line -had a probability of undergoing chain scission was higher than the probability of being formed by chain scission of low abundance higher-MW PEG molecules. As a result, the abundance of high-MW PEG molecules continuously decreased with increasing 𝑆𝚤𝐶 """"" s -as shown as blue trace for PEG with MW = 6380 Da in Figure . For 𝑆𝚤𝐶 """"" < 1.5, PEG molecules with intermediate MWs -highlighted for an exemplary MW of 4400 Da in Figure in purple -had a lower probability of reacting away than of being formed through scissions on higher MW PEGs, thereby resulting in an increase in relative abundance (shown as purple trace for PEG with MW = 4400 Da in Figure ). Beyond 𝑆𝚤𝐶 """"" = 1.5, however, these PEG molecules had a higher probability of reacting than being formed, resulting in a slow but continuous decrease in their relative abundance with increasing 𝑆𝚤𝐶 """"" . Finally, low MW PEG molecules (exemplary MW of 440 Da as green line; Figure ) had a probability of formation that exceeded the probability of reaction up to the highest simulated 𝑆𝚤𝐶 """"" = 8. Consequently, the abundance of the low MW PEG molecules continuously increases as 𝑆𝚤𝐶 """"" increases (shown for MW= 440 Da in green in