Well my guess is that the suffix copolyol (if you will lol) makes it water soluble. Like the addition of the PEG denotes that anything following it is water soluble.
Since the part in parentheses has the PEG in it, I'm guessing that makes it water soluble.
In short, the PEG as well as the copolyol denote that the original molecule (dimethicone) has been modified. In our case PEG means that its been modified in a way that makes it water soluble. I'm sure you knew most of that, just sorta explaining it outloud to myself
I can't find proof -- but it is listed in several places as an emulsifier and surfactant. Interesting trivia.
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