Synthesis of miktoarm star-shaped polymers with polyoxazoline arms and macrocyclic calix[8]arene branching center

A novel approach to the synthesis of miktoarm star-shaped poly(2-alkyl-2-oxazolines) with calix[8]arene core was developed using a combination of the “core first” (grafting from) and “grafting onto” methods. The star-shaped polymers of A₈B₈ type with grafted poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) arms were obtained using calix[8]arene based multifunctional branching center with sulfonyl chloride initiating moieties and as well as acyl hydrazide termination ones. The polymer structure has been confirmed by ¹H NMR spectroscopy and UV spectroscopy. The molar mass characteristics of the samples were determined by size-exclusion chromatographic and light scattering. It was experimentally confirmed that all synthesized polymers had the target arm number, namely 8 or 16. The obtained miktoarm stars were characterized by narrow molar mass distributions, and the polymerization degree of the arms was 15. The synthesized stars had a high intramolecular density, which increased with the arm number. It is shown that the thermoresponsiveness of the studied stars depends on the number and structure of arms and on intramolecular density, while molecular mass is not a decisive factor determining their LCST behavior.

For miktoarm stars, phase separation temperatures do not depend on the grafting configuration of poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) on the upper or lower rim of calix[8]arene.