production of selected secondary metabolites in transformed ...

number of free radicals is very low, the termination is reduced and the polymerization proves
living character.
P –X + Cu –Y/2L ⎯⎯→ P + M + X–Cu –Y/2L
I kakt
•
II
n ←⎯ ⎯ k
n
deakt
Pn + Pm
Fig. 2: Scheme of ATRP
The dormant species are mostly alkylhalides, from which the halogen atom is transferred to
catalyst (copper halide + organic ligand); the specie then becomes a radical, efficient to
propagate radical polymerization. The oxidation state of copper increases by one with
admitting the halogen; with the transfer back to the polymer the original oxidation state is
retrieved. Other transition-metal salts can be used as the ATRP catalyst, with the requirement
to the metal center to have at least two readily accessible oxidation states separated by one
electron.
A variety of monomers have been successfully polymerized using ATRP, typical
monomers include styrenes, methacrylates, acrylamides and acrylonitrile.
In ATRP, alkylhalides are typically used as the initiator. A variety of transition-metal
complexes have been studied as ATRP catalyst, but copper catalysts are superior in ATRP in
terms of versatility and cost. Presence of organic ligand is necessary for dissolution of copper
salt in reaction mixture. Above all, the nitrogen-based ligands are used (e.g. bipyridine,
PMDETA, HMTETA).
Initiation of ATRP with the POSS-based initiator has not been intimately described so far,
only some notes were published [5, 6]; however initiation of ATRP with polysiloxane-based
initiators has been described [7, 8] much more and due to the silimilar structures the depicted
techniques might be used also for POSS-based initiators.
EXPERIMENTAL
Materials used
Styrene was distilled from calcium hydride prior to use. Tetrahydrofurane was distilled
from purple sodium/benzophenon solution. Copper (I) bromide was stirred in glacial acetic
acid overnight, decanted, then washed with absolute ethanol and diethyl ether and vacuum
dried at 60°C. Ethyl-α-bromo-isobutyrate (EBIB), p-dimethoxybenzene (DMB), POSShydride,
allyl-bromoisobutyrate, pentamethyldiethylene triamine (PMDETA), and Karstedt
catalyst were used as received.
Synthesis of POSS-Br
POSS-Br was synthesized using hydrosilylation reaction. 1.37 g (1.44 mmol) of POSS-H,
16 ml dried THF, 0,24 ml (1.44 mmol) allyl-α-bromoisobutyrate and 55μL of Karstedt
catalyst solution in xylene (3 wt.%, 3,64 μmol) were placed into a 50 mL two-neck roundbottom
flask under nitrogen blanket and stirred. The flask was fit with rubber septum and a
Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006
Sekce DSP 2006, strana 229
kp
k´t
P • m
kt
Pn+m