production of selected secondary metabolites in transformed ...

eflux condenser equipped with bubble flask filled with silicon oil. Then 55μL of Karstedt
catalyst solution in xylene (3 wt.%, 3,64 μmol) was injected to the reaction flask and the
mixture was heated in 80 °C oil bath under reflux for 24 hours. THF was evaporated and the
product POSS-Br was vacuum dried.
R
R
R
Si
O
O
Si O
O Si
O
R
Si
O
O
R
O
Si
Si O
O Si
O
O
Si
R
H
C
H 3
R
+
C
H 2
RH3
= C
O
O
CH 3
Br
CH 3
Karstedtův Karstedt's katalyzátor catalysator catalyst
THF, reflux
24 hours
Fig. 3: Synthesis of POSS-Br initiator
Polymerizations
Polymerization 1:
A typical polymerization is as follows: 31 mg CuBr was placed into a 50 mL double-neck
flask; the flask was evacuated and filled with nitrogen. Under a nitrogen blanket 5 mL of
styrene, 40 μL of PMDETA and 4.6 g of p-dimethoxybenzene was added. The mixture was
stirred until a homogenous solution formed and was placed into a 120°C oil bath under
nitrogen. After heating to the reaction temperature 0,48 g of POSS-Br (initiator) was added.
The solution turned dark green as the reaction began. Periodically, small amounts of reaction
mixture were removed for kinetic and molecular weight analysis (conversion was
determinated by weight analysis, molecular weight of polymers was determined using gel
permeation chromatography). Molar ratios: Styrene:POSS-Br:CuBr:PMDETA -
100:1:0.5:0.5.
Polymerization 2:
This polymerization is similar to the polymerization 1, except the POSS-Br initiator is
replaced with 65 μL of ethyl-α-bromo-isobutyrate, which was injected to the hot mixture via
rubber septum. Molar ratios: Styrene:EBIB:CuBr:PMDETA - 100:1:0.5:0.5.
RESULTS
Reason for using POSS as an initiator of ATRP is to get a polystyrene macromolecule with
one bulky POSS group at one of the chain ends; the initiator of ATRP remains the inseparable
part of the macromolecule.
Molecular weight plots prove living character of polymerizations; molecular weight grows
linearly with conversion, with conversion growing to almost 100%. Linear dependence of
conversion on time in semi logarithmic coordinates (Fig. 5) shows the first-order kinetic with
respect to monomer.
From the molecular weight plot of polymerization 1 (Fig. 6) it is obvious, that initiation
efficiency is low and only about one half of the POSS initiator molecules is used for
initiation; this causes the molecular weight to be twice as high as is should be according to the
theoretical value determined from molar ratio monomer:initiator. In contrast, polymerization
2 initiated with low molecular weight initiator EBIB behaves in accordance with theory
(Fig. 7).
R
R
O
Si
O
R
Si
O
O
Si
O
R
Si
O
Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006
Sekce DSP 2006, strana 230
O
Si
O
O
Si
R
R
O
O
Si
Si
O
R
O
O
CH 3
Br
CH 3