Bosses can drop Chempacks for different lieutenant factions. These Chempacks can be used to increase level caps for individual lieutenants from specific factions.
Chempacks has 5 different rarities (common (I)/uncommon (II)/rare (III)/epic (IV) /legendary (V)). Different upgrade levels will require Chempacks of different rarity and need to be done in order.
Keep in mind there is no single Boss can drop Chempacks for ALL factions. So please check the Boss reward before hunting for desired Chempacks.
In the current boss loot system, only common (I) /uncommon (II) /rare (III) Chempacks can be looted, epic (IV) and legendary (V) can only be made through the Tech Lab. There is a new "Chempack" section in Tech Lab where Chempack IV and V can be obtained.