Water soluble star block poly(oxazoline) with porphyrin label: a unique emulsion and its shape direction

Abstract

Water soluble star polymers consisting of a porphyrin center and four poly(oxazolines) arms such as Por-[poly(methyloxazoline)]₄ (1), Por-[poly(ethyloxazoline)]₄ (2), Por-[poly(methyloxazoline-co-ethyloxazoline)]₄ (3) and Por-[poly(methyloxazoline)-b-poly(ethyloxazoline)]₄ (4) were synthesized and used for the investigation of their unusual behavior in a water–chloroform medium. Thanks to the porphyrin color label, we were easily able to visualize that the color in the water in which the star 2 with the poly(ethyloxazoline) (PEOX) arm was dissolved was transferred to the chloroform as a small amount of chloroform was added to the water solution. In contrast, the color in the chloroform was transferred to the water phase in case of the star 1 with poly(methyloxazoline) (PMOX) arms. Using UV-Vis and ¹H NMR protocols, we demonstrated that the star 1 with PMOX arms is more easily soluble in water than in chloroform, but the star 2 having PEOX arms is more easily soluble in chloroform than in water. As a reflection of such contrasting solubilities of PMOX and PEOX, the star 4 consisting of PMOZ-b-PEOZ resulted in water-in-chloroform (W/O) and chloroform-in-water (O/W) emulsions bearing porphyrin residues. In these emulsions, the PMOX block towards water and the PEOX block carrying the porphyrin residues towards chloroform. The emulsions were stable in shape and were used as templates in the sol–gel reaction of TEOS to give poly(oxazoline)–silica hybrid hollow spheres embedding a photofunctional porphyrin.