Design of effective systems for controlled radical polymerization of ...

354 U. S. Schubert, G. Hochwimmer, Ch. E. Spindler, O. Nuyken
Fig. 5. UV/VIS spectra: curve (a): polystyrene obtained in the presence of 2; curve (b): polystyrene
obtained from autopolymerization; curve (c) 20 lg 2 added to 1 mg of polystyrene (in
CHCl 3 :CH 3 CN = 5:1). Concentrations: (a) 0.50 mg PS/mL; (b) and (c) 0.46 mg PS/mL
Fig. 6. Dependence of monomer conversion as function of
time in the polymerization of styrene at 758C in the presence of
4 ([(CH 3 ) 2 CHO] 3 Al: 0.292 mmol; styrene: 51 mmol; ratio 4: (1-
bromoethyl)benzene = 1:2; ratio 4: monomer = 1:700)
Fig. 7. Dependence of molecular weights (f) and polydispersities
(9) as function of monomer conversion in the polymerization
of styrene at 758C in the presence of 4 ([(CH 3 ) 2 CHO] 3 Al:
0.292 mmol; styrene: 51 mmol; ratio 4: (1-bromoethyl)benzene
= 1:2; ratio 4: monomer = 1:700)
styrene obtained from autopolymerization gave a significant
p-p* transition band (Fig. 5, curve c). Therefore it
can be concluded, that the content of copper in the sample
is less than 150 ppm. First experiments utilizing AAS
gave a copper content of 210 ppm (compared to 150 ppm
of a polystyrene obtained from autopolymerization). The
aluminium content is lower than 2.5 ppm (flame AAS).
Polymerization of styrene utilizing bipyridine/metal salt
mixtures gave polymers with a copper content of 2000 to
2500 ppm.
Similar linear relationships between molecular weights
of the polystyrenes on conversion and conversion on time
could be observed when 2 was replaced by 5,59-dimethyl-
2,29-bipyridine copper(II) complex 4 in the reaction mixture
(Fig. 6 and 7). However, using 4 the polymerization
rate drops to the half (e.g. 20% conversion after 30 h for
4 compared to 40% conversion after 30 h for 2). The
observed polydispersities vary between 1.2 and 1.4
(Tab. 2). However, in this case narrow molecular weight
distributions could be found already at low conversions.
Further investigations using 6,69-dimethyl-2,29-bipyridine
copper complexes are in progress. First results showed a
very fast polymerization up to 10% conversion with quite
broad polydispersities.