Microwave-assisted synthesis and properties of a series of poly(2-alkyl-2-oxazoline)s

Abstract

Microwave-assisted organic synthesis is a quickly expanding field of research. The fast non-contact (super)heating of the reaction mixtures has already resulted in many examples of increased reaction rates and improved yields. However, the number of investigations focusing on microwave-assisted polymerizations, and especially living/controlled polymerizations, is still limited. Following our recent success in accelerating the cationic ring-opening polymerization of 2-oxazolines, we report here our studies on the cationic polymerization of a series of linear 2-alkyl-2-oxazolines under microwave irradiation. The effect of chain length on the polymerization kinetics was investigated. Moreover, the microwave polymerization of 2-ethyl-2-oxazoline was further investigated by 1 H-NMR spectroscopy to determine the active species during the polymerization. Besides the microwave polymerization of the linear 2-alkyl-2-oxazoline monomers, the thermal and surface properties of the resulting polymers were investigated by DSC and contact-angle measurements to study the effect of side-chain length on the polymer properties.

Poly(2-cyclopropyl-2-oxazoline): From Rate Acceleration by Cyclopropyl to Thermoresponsive Properties

“…The lower steric bulk of cyclopropyl compared to n-propyl or isopropyl most likely does not influence the polymerization rate since it has been demonstrated that 2-oxazolines with ethyl to n-nonyl substituents all have similar polymerization rates. 30 At higher conversion (>80%), the solution became very viscous explaining the observed decrease in polymerization rate due to limited diffusion. This can also explain the slightly slower polymerization rate at higher [ 33 On the basis of the kinetic investigations, six CPropOx polymers with different degrees of polymerization (DP) were synthesized under microwave-assisted conditions using MeOTs as initiator and acetonitrile as solvent.…”

“…29 The polymerization kinetics of CPropOx was determined at 140°C, using an initial monomer concentra- 30 while in contrast iPropOx polymerizes slower than nPropOx. 18 In fact, the k p of CPropOx is the fastest reported so far for a 2-oxazoline with an aliphatic side chain; only 2-phenyl-2-oxazolines with electronwithdrawing o-fluoro groups were slightly faster.…”

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

“…The investigated poly(2-oxazoline)s (see Scheme 1; the polymers will be abbreviated by the monomer names as given in Scheme 1 in the following discussion) were prepared by microwave-assisted polymerization of the corresponding monomers using methyl tosylate as initiator and acetonitrile as solvent as described in our previous publication [47]. The monomers were prepared by reaction of the corresponding nitriles with 1-amino-2-ethanol using zinc acetate as catalyst [48].…”

Thermal Properties of Methyl Ester-Containing Poly(2-oxazoline)s

“…Dry solvents were obtained from a solvent purification system from J.C. Meyer, with aluminum oxide drying system and a nitrogen flow. MestOx [37], C3MestOx [38], and nPropOx [48] were prepared according to literature procedures. In this paper we describe the synthesis and thermal properties of methyl ester-containing PAOx.…”