By means of probability theory, the sol fraction of an A(a1)B(b1)-A(a2
)B(b2) type copolymerisation reaction, in which intramolecular reactio
ns are neglected, is investigated in the post-gel regime to give the g
elation condition explicitly. (A(a1)B(b1) is a monomer with a1 functio
nal groups of type A and b1 functional groups of type B.)