In free radical addition polymerizations sometimes chain transfer agents are added. From what I understand chain transfer agents (e.g. XR' below) reduce the average molecular weight by transferring the free radical from the growing polymer chain (P•) to another molecule (R'•).
P• + XR' → PX + R'•
My question is what effect would this have on the overall "rate" of polymerization itself, i.e say the consumption of monomer.
In other words the R'• species is then free to combine with more Monomer, right? And being a smaller molecule (in general) would it be expected to have a higher rate constant for the reaction:
R'• + M--> P•