Premium
Termination kinetics of styrene free‐radical polymerization studied by time‐resolved pulsed laser experiments
Author(s) -
Buback Michael,
Kowollik Christopher,
Kurz Caroline,
Wahl Almut
Publication year - 2000
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/(sici)1521-3935(20000201)201:4<464::aid-macp464>3.0.co;2-4
Subject(s) - kinetics , radical polymerization , polymer chemistry , styrene , polymerization , photochemistry , chemistry , materials science , copolymer , organic chemistry , polymer , physics , quantum mechanics
The single pulse (SP)‐pulsed‐laser polymerization (PLP) technique has been applied to measure k t / k p , the ratio of termination to propagation rate coefficients, for the free‐radical bulk polymerization of styrene at temperatures from 60 to 100°C and pressures from 1800 to 2 650 bar. k t / k p is obtained by fitting monomer concentration vs. time traces that are determined via time‐resolved (μs) near infrared monitoring of monomer conversion induced by single excimer laser pulses of about 20 ns width. Styrene is a difficult candidate for this kind of measurements as conversion per pulse is small for this low k p and high k t monomer. Thus between 160 to 300 SP signals were co‐added to yield a concentration vs. time trace of sufficient quality for deducing k t / k p with an accuracy of better than ± 20 per cent. With k p being known from PLP–SEC experiments, chain‐length averaged k t values are immediately obtained from k t / k p . At given pressure and temperature, k t is independent of the degree of overall monomer conversion, which, within the present study, has been as high as 20%percnt;. The k t value, however, is found to slightly increase with the amount of free radicals produced by a single pulse in laser‐induced decomposition of the photoinitiator DMPA (2,2‐dimethoxy‐2‐phenyl acetophenone). This remarkable observation is explained by DMPA decomposition resulting in the formation of two free radicals which significantly differ in reactivity. Extrapolation of SP–PLP k t data from experiments at rather different DMPA levels and laser pulse energies toward low primary free‐radical concentration, yields very satisfactory agreement of the extrapolated k t values with recent literature data from chemically and photochemically induced styrene polymerizations.