Initiator Effect on the Cationic Ring-Opening Copolymerization of 2-Ethyl-2-Oxazoline and 2-Phenyl-2-Oxazoline
-
Fijten, Martin W. M.; Hoogenboom, Richard; Schubert, Ulrich S.
- Abstract:
- The aim of this research was to study the effect of the initiator on the
resulting monomer distribution for the cationic ring-opening copolymerization of 2-
ethyl-2-oxazoline (EtOx) and 2-phenyl-2-oxazoline (PhOx). At first, kinetic studies
were performed for the homopolymerizations of both monomers at 160 8C under
microwave irradiation using four initiators. These initiators have the same benzylinitiating
group but different leaving groups, Cl, Br, I, and OTs. The basicity of
the leaving group affects the ratio of covalent and cationic propagating species and,
thus, the polymerization rate. The observed differences in polymerization rates could
be correlated to the concentration of cationic species in the polymerization mixture as
determined by 1H NMR spectroscopy. In a next-step, polymerization kinetics were
determined for the copolymerizations of EtOx and PhOx with these four initiators.
The reactivity ratios for these copolymerizations were calculated from the polymerization
rates obtained for the copolymerizations. This approach allows more accurate
determination of the copolymerization parameters compared to conventional methods
using the composition of single polymers. When benzyl chloride (BCl) was used as an
initiator, no copolymers could be obtained because its reactivity is too low for the polymerization
of PhOx. With decreasing basicity of the used counterions (Br
> I
>
OTs), the reactivity ratios gradually changed from rEtOx ¼ 10.1 and rPhOx ¼ 0.30 to
rEtOx ¼ 7.9 and rPhOx ¼ 0.18. However, the large difference in reactivity ratios will
lead to the formation of quasi-diblock copolymers in all cases. In conclusion, the used
initiator does influence the monomer distribution in the copolymers, but for the
investigated system the differences were so small that no difference in the resulting
polymer properties is expected.
- Year:
- 2008
- Type of Publication:
- Article
- Keywords:
- kinetic investigation; living polymerization; microwave irradiation; statistical copolymers; 2-oxazolines
- Journal:
- Journal of Polymer Science: Part A: Polymer Chemistry
- Volume:
- 46
- Pages:
- 4804 - 4816