Fundamental molecular weight distribution of RAFT polymers

The molecular weight distribution formed in an ideal reversible addition-fragmentation chain transfer (RAFT)-mediated radical polymerization is considered theoretically. In this polymerization, the addition to the RAFT agent is reversible, and the active period on the same chain could be repeated, via the two-armed intermediate, with probability 1/2. This possible repetition is accounted for by introducing a new concept, the overall active/dormant periods. With this method, the apparent functional form of the molecular weight distribution (MWD) reduces to that proposed for the ideal living radical polymers (Tobita, Macromol. Theory Simul. 2006, 15, 12). The repetition results in a broader MWD than without the repetition. The formulae for the average molecular weights formed in batch and a continuous stir red tank reactor are also presented.