Microwave-assisted polymerization of 2-oxazolines: ionic liquids as solvents and fluorinated aromatic monomers

The use of microwave-irradn. instead of conventional heating has been demonstrated to result in faster and cleaner reactions and in some cases to different selectivity. In our previous work, we have demonstrated that the use of pressurized microwave conditions results in a tremendous acceleration for the cationic ring-opening polymn. of 2-oxazolines. However, this obsd. acceleration could be reproduced using conventional heating in an autoclave. Nonetheless, the control over the polymn. was slightly better under microwave irradn. due to the more homogeneous temp. profile. This improved control over the polymn. allowed the synthesis of well-defined triblock and tetrablock copoly(2-oxazoline)s for the first time. In this contribution, the use of ionic liqs., which are well-known as excellent microwave absorbers, as solvent for the microwave-assisted cationic ring-opening polymn. of 2-ethyl-2-oxazoline is discussed. In addn., a continuous flow operating procedure is proposed, in which the poly(2-ethyl-2-oxazoline) is extd. with water and the ionic liq. is reused for the polymn. after removal of the residual water using a microwave-assisted distn. The second part of this contribution deals with the microwave-assisted cationic ring-opening polymn. of fluorinated 2-phenyl-2-oxazolines. These monomers have never been considered for polymn. since the electron withdrawing substituents on the arom. system were thought to result in too slow polymn. Nonetheless, the accelerated microwave-assisted polymn. procedure allowed the polymn. of these monomers, whereby surprisingly fast polymns. were obtained for monomers with ortho-fluoro substituents. [on SciFinder (R)]