When you say it releases X kJ/mol, are you using moles of B or moles of oligomer/polymer?
If you use moles of B, then X will be pretty much constant. If you use moles of oligomer or polymer, then it will be more variable depending on molecular weight. So this is usually done using moles of B.
You can use grams for the oligomer/polymer and it will also be pretty much constant - this is sometimes the way it might be calculated for practical considerations.
Will it react with stoichiometric amount of B? more or less. Sometimes in high MW polymers there can be mass transport issues and side reactions that make it less than 100%.