Summary: The ring‐opening cationic polymerization of 2‐ethyl‐2‐oxazoline was performed in a single‐mode microwave reactor as the first example of a microwave‐assisted living polymerization. The observed increase in reaction rates by a factor of 350 (6 h → 1 min) in the range from 80 to 190 °C could be attributed solely to a temperature effect as was clearly shown by control experiments and the determined activation energy. Because of the homogenous microwave irradiation, the polymerization could be performed in bulk or with drastically reduced solvent ratios (green chemistry).Monomer conversion, represented by the ratio ln{[M0]/[Mt]}, plotted against time for six temperatures in the range from 80 to 180 °C, and polymerization reaction vials, showing an increase in yellow color for those reactions performed (well) above and below 140 °C, indicating side reactions.magnified imageMonomer conversion, represented by the ratio ln{[M0]/[Mt]}, plotted against time for six temperatures in the range from 80 to 180 °C, and polymerization reaction vials, showing an increase in yellow color for those reactions performed (well) above and below 140 °C, indicating side reactions.
A library of 4 chain-extended homo- and 12 diblock copoly(2-oxazoline)s was prepared from
2-methyl-, 2-ethyl-, 2-nonyl-, and 2-phenyl-2-oxazoline within less than a day (total net reaction time).
The living cationic ring-opening polymerization was initiated by methyl tosylate and performed in
acetonitrile at 140 °C in a single-mode microwave reactor. A total number of 100 (50 + 50) monomer
units was incorporated into the respective polymer chains; the thus-obtained 16 polymers exhibited narrow
average molecular weight distributions (PDI < 1.30). All compounds were stable up to temperatures of
(at least) 300 °C. The subsequent determination of the glass-transition temperatures and the specific
heats revealed a significant influence of the type of substituents attached to the polymers' backbones:
the glass-transition temperature as well as the corresponding specific heat increased with an increasing
rigidity of the substituents in the polymer (phenyl/methyl vs nonyl/ethyl).
Summary: Gel permeation chromatography (GPC) and gas chromatography (GC) were successfully introduced into a high‐throughput workflow. The feasibility and limitations of online GPC with a high‐speed column was evaluated by measuring polystyrene standards and comparison of the results with regular offline GPC measurements. The reliability of the online GC characterization was investigated by monitoring the cationic ring‐opening‐polymerization of 2‐ethyl‐2‐oxazoline, whose polymerization kinetics were determined by both online and offline GC.
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