Synthesis and crystal structures of multifunctional tosylates as basis for star-shaped poly(2-ethyl-2-oxazoline)s

Abstract

SummaryThe synthesis of well-defined polymer architectures is of major importance for the development of complex functional materials. In this contribution, we discuss the synthesis of a range of multifunctional star-shaped tosylates as potential initiators for the living cationic ring-opening polymerization (CROP) of 2-oxazolines resulting in star-shaped polymers. The synthesis of the tosylates was performed by esterification of the corresponding alcohols with tosyl chloride. Recrystallization of these tosylate compounds afforded single crystals, and the X-ray crystal structures of di-, tetra- and hexa-tosylates are reported. The use of tetra- and hexa-tosylates, based on (di)pentaerythritol as initiators for the CROP of 2-ethyl-2-oxazoline, resulted in very slow initiation and ill-defined polymers, which is most likely caused by steric hindrance in these initiators. As a consequence, a porphyrin-cored tetra-tosylate initiator was prepared, which yielded a well-defined star-shaped poly(2-ethyl-2-oxazoline) by CROP as demonstrated by SEC with RI, UV and diode-array detectors, as well as by 1H NMR spectroscopy.

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

“…Structural formulae of a hexatosylate initiator and the corresponding star-shaped pEtOx (for details, see reference [118]). …”

“…Unlike in other multivalent initiators, the functional groups of this type of multifunctional initiator proved to be of comparable reactivity, and the polymerization rate correlated linearly with the number of functional groups. Hence, this class of initiators enables the rational design of star-shaped poly(2-oxazoline)s. The preparation of well-defined polymer architectures using CROP of 2-oxazolines was the aim of Hoogenboom, Schubert et al (Scheme 9) [118]. They synthesized various multifunctional tosylates of dendritic shape by esterification of alcohols with tosyl chloride.…”

Systematic investigation of alkyl sulfonate initiators for the cationic ring-opening polymerization of 2-oxazolines revealing optimal combinations of monomers and initiators

“…Nonetheless, based on three independent reports on using sulfonate esters of pentaerythritol for the preparation of star-shaped poly(2-oxazolines) [16][17][18] it may be suggested that nosylates and triflates are better initiators than tosylates.…”

Amphiphilic photo-induced triblock polyoxazoline through coumarin dimerization: Efficient synthetic tool for nanoparticles

“…The POx could be also combined to other polymerization processes [46]. All these strategies explained the keen interest of the manifold investigations on the decoration of POx using functional terminating agents [47] or initiators [48][49][50][51][52][53][54][55][56][57][58]. Recently, we described the synthesis of amphiphilic diblock polyoxazolines (Cm-POx n ) bearing an UV-sensitive coumarin end-group (Fig.…”