Microwave-Assisted Cationic Ring-Opening Polymerization of 2-Oxazolines:  A Powerful Method for the Synthesis of Amphiphilic Triblock Copolymers

Abstract

We report on the first successful example of the preparation of triblock copolymers via a cationic ring-opening polymerization procedure. A library of 30 triblock copolymers was prepared from 2-methyl-, 2-ethyl-, 2-nonyl-, and 2-phenyl-2-oxazoline in a single-mode microwave reactor. The polymers exhibited narrow molecular weight distributions and showed only minor deviations from the targeted monomer ratio of 33:33:33. The glass-transition temperature of the triblock copolymers spanned the range from 50 to 100 °C depending on the incorporated monomers. The micellization behavior was investigated for some amphiphilic triblock copoly(2-oxazoline)s containing two hydrophilic and one hydrophobic blocks. The size of the micelles was larger when the hydrophobic block is located at one end of the triblock copoly(2-oxazoline)s, as measured by atomic force microscopy and dynamic light scattering.

Bioinspired Poly(2-oxazoline)s

“…The self-assembly of triblock and tetrablock copoly(2-oxazoline)s based on MeOx, EtOx, NonOx and PhOx was demonstrated by Schubert et al [70,71]. Recently, more detailed investigations on the micellization of these copolymers were reported in solvent mixtures of ethanol and water [72].…”

Design Strategies for Functionalized Poly(2-oxazoline)s and Derived Materials

“…Preceded by a study of homopolymerizations [157], research examples comprise a 16-membered library of four chain-extended homo-and 12 diblock copoly(2-oxazoline)s [158], as well as the synthesis of the corresponding tri- [159] and tetrablock copoly(2-oxazoline)s [160]. Scheme 13.…”

Poly(2‐oxazoline)s: Alive and Kicking

“…[45] Nevertheless, the improved microwave-assisted polymerization procedure allowed the synthesis of a 30-membered library of relatively well-defined triblock copoly(2-oxazoline)s (PDI < 1.30) by the sequential monomer addition procedure. [46] These triblock copolymers are based on MeOx, EtOx, NonOx, and PhOx, whereby each block consists of 33 monomer units. Similarly to the diblock copoly(2-oxazoline)s, the T g s of these triblock copolymers span a range from 50 to 110 8C, whereby all polymers with both a pNonOx and a pPhOx block show no T g , and all polymers with a pNonOx block reveal a melting point around 150 8C.…”