Molecular-Weight Distribution of Living Chains in Polystyrene Prepared by Reversible Addition-Fragmentation Chain-Transfer Polymerization

We report on the chromatographic separation and characterization of living chains in polystyrene prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization. To achieve full chromatographic resolution of different living and dead chains, a polystyrene with distinctive end groups was prepared in RAFT polymerization by using a specially designed chain-transfer agent (R-S-(C=S)-S-Z) with polar hydroxyl end groups at both R and Z and a thermal initiator without hydroxyl group, 2,2'-azobis(isobutyronitrile). The structures of separated living chains derived from the RAFT agent and initiator were characterized using H-1 nuclear magnetic resonance and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Molecular-weight distribution (MWD) of the living chains derived from the RAFT agent is close to the Poisson distribution. However, the living chains grown from the initiator have a broader MWD with low-molecular-weight tailing. As the [initiator]/[RAFT agent] ratio increases, both the amount and the dispersity of the living chains initiated by the initiator fragment increase while the MWD of the living chains initiated by the fragment of the RAFT agent remains unchanged.