Premium
Chain‐length dependent termination in pulsed‐laser polymerization, 5 . The evaluation of the rate coefficient of bimolecular termination k t for the reference system styrene in bulk at 25°C
Author(s) -
Olaj Oskar Friedrich,
Vana Philipp
Publication year - 1998
Publication title -
macromolecular rapid communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 154
eISSN - 1521-3927
pISSN - 1022-1336
DOI - 10.1002/(sici)1521-3927(19980801)19:8<433::aid-marc433>3.0.co;2-g
Subject(s) - polymerization , degree of polymerization , chain termination , chain (unit) , styrene , moment (physics) , analytical chemistry (journal) , thermodynamics , chemistry , radical polymerization , polymer chemistry , physics , materials science , polymer , nuclear magnetic resonance , copolymer , chromatography , quantum mechanics
Following earlier suggestions the values for the rate coefficient of chain termination k t in the bulk polymerization of styrene at 25°C were formally calculated (a) from the second moment of the chainlength distribution (CLD) and (b) from the rate equation for laser‐initiated pseudostationary polymerization (both expressions originally derived for chain‐length independent termination) by inserting the appropriate experimental data including the rate constant of chain propagation k p . These values were treated as average values, k t mand k t *, respectively. They exhibited good mutual agreement, even the predicted gradation ( k t m< k t *by about 20%) was recovered. The log‐log plot of k t vs. the number‐average degree of polymerization of the chains at the moment of their termination yielded exponents b of 0.16–0.18 in the power‐law k t = A · P n −b , A ranging from 2.3 × 10 8 to 2.7 × 10 8 L · mol −1 · s −1 . These data are only slightly affected if termination is not assumed to occur by recombination only and a small contribution of disproportionation is allowed for.