New azonitrile initiators carrying N-hydroxysuccinimide (ACPS) or biotin derivative (ACP-LC-B) moieties were synthesized from 4,4’-azobis(4-cyanopentanoic acid) (ACPA) with a yield of around 60%. Special care was taken in the assignment of the C-13-NMR resonances of the ACP-LC-B. The kinetic and thermal parameters associated with these initiators were determined by UV spectroscopy and differential scanning calorimetry. The decomposition rate constants (k(d)) versus temperature are similar for both ACPA and ACPS initiators and are in good agreement with literature data. The activation energies (E(alpha)) values are 132, 140, and 98 kJ mol(-1); and the frequency factors are (in A) 34, 35, and 25 for ACPA, ACPS, and ACP-LC-B, respectively. Solution polymerization of N-vinylpyrrolidone (NVP) in dimethylformamide initiated with ACPA and ACPS showed similar kinetic behavior with a k(p)/k(t)(1/2) value of 0.23 (L mol(-1) s(-1))(1/2). This low value and the low molecular weights of the polymers were explained by variations in the initiator efficiencies, as a function of the monomer concentration, as well as by the high chain transfer activity of the solvent. Functionally terminated P(NVP) was evidenced by gel permeation chromatography and an immunoassay test, suggesting that the average number of bioreactive groups per polymer chain was one.