The decomposition rate constants kd of initiators can be determined by a new method directly in monomers as solvents. If a suitable inhibitor is added to a monomer mixture with the initiator the latter decomposes nearly without monomer conversion. The initiator concentration—after the inhibitor is consumed—can be found by means of the dilatometrically determined polymerization rate after the induction period. The functional connection between polymerization rate and initiator concentration found without inhibitor is used as a calibration curve for that purpose. The dilatometrical measurements were made in the monomers styrene and N‐vinyl‐2‐pyrrolidone using 2,2′‐azoisobutyronitrile (AIBN) as initiator and p‐quinone as inhibitor. The following decomposition rate constants were found: kd=1,52 · 10−5 S−1 (styrene) and kd=1,62 · 10−5 S−1 (N‐vinyl‐2‐pyrrolidone), which is in agreement with literature values. Initiator efficiencies f were calculated: f=0,46 (styrene), f=0,47 (N‐vinyl‐2‐pyrrolidone). In methyl methacrylate (MMA) 2,2′‐diphenyl‐1‐picrylhydrazyl (DPPH) was used as inhibitor. Under certain conditions the product kdf can be calculated from the consumption rate of DPPH. The value found in MMA (kdf=3,7 · 10−6 s−1) is lower than that reported in literature (6,45 · 10−6 s−1).
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Braun et al. (1978) studied this question.