i assume you're talking about the 'follow-up' damage that happens the round after a vitrolic blast strikes someone.
i'd think it would do the full 2d6, as the invocation says nothing otherwise; however, the eldritch chain does seem to indicate that initial eldritch blast damage is halved, but is silent on additional effects.
considering that neither reading of the invocations really make it overpowered, i'd just go for the interpretation that it does the full 2d6 on any follow-up round.
