Synthesis and characterization of the polymer brushes with alternated polyoxazoline side chains

An original approach to the synthesis of a new promising class of thermo-sensitive polymers, polymer brushes with regularly alternating grafted poly(2-alkyl-2-oxazoline) chains (PAOx), is proposed based on the "grafting through" scheme. At first, poly(2-alkyl-2-oxazoline) macro-monomers were obtained with styrene and maleimide terminal functions by the cationic ring-opening polymerization of 2-ethyl- and 2-isopropyl-2-oxazolines. Then, polymer brushes (PAOx-PB) with alternating-side polyoxazoline chains were synthesized via radical polymerization in chlorobenzene solution initiated by azobisisobutyronitrile. Reactivity ratios of the macro-monomers were determined by the Fineman–Ross (r = 0.013; r = 0.107) and the Kelen–Tüdős (r = 0.012; r = 0.105) methods, indicating that their copolymerization results in the formation of a polymer brush with an alternating sequence of macro-monomer units in the backbone. Molecular weight characteristics of obtained PAOx-PB were determined by means of size-exclusion chromatography and static light-scattering. The resulting PAOx-PB have unimodal molecular weight distribution, a rather low degree of polymerization of the main chain and the number of side chains in the range of f = 10–20. The structure and monomer content of synthesized PAOx-PB were studied using HNMR spectroscopy. It was shown that they have equivalent contents of PEtOx and PIPrOx side chains. The high intramolecular density of PAOx-PB macromolecules and, accordingly, the strong folding of the side chains was indicated. Graphical abstract: (Figure presented.)