if it were dissolved, it would be entrained, but this is not the case here. It looks like this is an unwanted reaction (from mitgebracht) so I wouldn't use "provided" or "added" which suggests that it is intentional. The oxygen is part of a free aryl ether (e.g. Ar-O-Ar) that cleaves apart (radical mechanism? photoinitiation? UV curing?) to give O-Ar groups that can add as a substituent to whatever is being synthesized (a polymer?). In this case, I would tend to go for "brought in" (which is also a direct translation, of course) or even "included"