Low-molecular-weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain-transfer agent (CTA). With a combination of NMR spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, the PAA end-groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain-ends and of the H-terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H-terminated chains. By quantifying the different end-groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction. (C) 2004 Wiley Periodicals, Inc.