Synthesis, Structure, Hydrodynamics and Thermoresponsiveness of Graft Copolymer with Aromatic Polyester Backbone at Poly(2-isopropyl-2-oxazoline) Side Chains.

Elena Tarabukina,Sergei S Sheiko,Alexander Filippov,Anna Krasova,Emil Fatullaev,Andrey Tenkovtsev,Mikhail Kurlykin

doi:10.3390/polym12112643

Abstract

New thermoresponsive graft copolymers with an aromatic polyester backbone and poly(2-isopropyl-2-oxazoline) (PiPrOx) side chains are synthesized and characterized by NMR and GPC. The grafting density of side chains is 0.49. The molar masses of the graft-copolymer, its backbone, side chains, and the modeling poly-2-isopropyl-2-oxaziline are 74,000, 19,000, 4300, and 16,600 g·mol−1, respectively. Their conformational properties in nitropropane as well as thermoresponsiveness in aqueous solutions are studied and compared with that of free side chains, i.e., linear PiPrOx with a hydrophobic terminal group. In nitropropane, the graft-copolymer adopts conformation of a 13-arm star with a core of a collapsed main chain and a PiPrOx corona. Similarly, a linear PiPrOx chain protects its bulky terminal group by wrapping around it in a selective solvent. In aqueous solutions at low temperatures, graft copolymers form aggregates due to interaction of hydrophobic backbones, which contrasts to molecular solutions of the model linear PiPrOx. The lower critical solution temperature (LCST) for the graft copolymer is around 20 °C. The phase separation temperatures of the copolymer solution were lower than that of the linear chain counterpart, decreasing with concentration for both polymers.

Highlights

Physicochemical properties of molecular brushes in solution and in the bulk strongly depend on architectural parameters, such as degree of polymerization of the main chain, length and grafting density of the side chains [1,2,3,4,5]
Polymers 2020, 12, 2643 synthetic and natural components such as cellulose and chitosan, which are used in many biomedical applications [12,13,14,15,16]
The chromatographic analysis was performed on the Shimadzu LC-20AD chromatograph equipped with TSKgel G5000HHR column (5 μm, 7.8 mm × 300 mm, Tosoh Bioscience, Tokyo, Japan) and a refractometric detector

Summary

Introduction

Physicochemical properties of molecular brushes (grafted copolymers) in solution and in the bulk strongly depend on architectural parameters, such as degree of polymerization of the main chain, length and grafting density of the side chains [1,2,3,4,5]. One of the ways to synthesize graft copolymers is the so-called polymerization-polycondensation reaction, whereby polycondensation yields the main chain, followed by grafting from polymerization of side chains [17,18,19,20]. For such high molecular weight compounds, most solvents are selective

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