Additional retardation in RAFT polymerization:: Detection of terminated intermediate radicals

The reversible addition-fragmentation chain transfer (RAFT) polymerization of N-acryloylmorpholine (NAM) is performed using three dithioesters (DT) as chain transfer agents (CTA) that incorporate a morpholine (morpholine-DT), a biotin (biotin-DT), or a sugar (sugar-DT) moiety in the R group. PolyNAM chains of controlled characteristics are synthesized. An unexpected behavior is observed with morpholine-DT, described as an 'additional retardation', which is especially visible when low molar masses are targeted ((M) over bar (n) < 5 000 g center dot mol(-1)). In that particular case, further investigations using MALDI-TOF mass spectrometry show the presence of terminated inter-mediate radicals (IRs), which corroborates the assumption based on a specific protection of IR according to the nature of the alpha-chain-end.