Amphiphilic polypeptide-polyoxazoline graft copolymer conjugate with tunable thermoresponsiveness: Synthesis and self-assembly into various micellar structures in aqueous and nonaqueous media

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Polymer, ISSN: 0032-3861, Vol: 110, Page: 12-24

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Avijit Bose; Somdeb Jana; Anupam Saha; Tarun K. Mandal
Elsevier BV
Chemistry; Materials Science
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A “grafting onto” approach based on two different controlled ring-opening polymerization (ROP) techniques is developed to synthesize polytyrosine- graft -poly(2-ethyl-2-oxazoline) (PTyr- g -PEtOx) copolymer conjugates of varying main backbone and pendent chain lengths. This approach consists of syntheses of propargyl functionalized polytyrosine (PTyr- O -Pr) by ROP of tyrosine N -carboxyanhydride and azide functional poly(2-ethyl-2-oxazoline) (PEtOx-N 3 ) by cationic ROP separately followed by their grafting using CuAAC reaction to afford the final graft copolymer conjugate (GCC). Owing to the presence of pendent hydrophiphilic PEtOx block, PTyr- g -PEtOx GCC exhibits LCST-type reversible phase transition behavior in water, which is tunable with respect to its concentration and the lengths of the main backbone and the pendent block. Again, the amphiphilic PTyr- g -PEtOx GCC molecules undergo self-assembly into spherical unit micelles and their consequent secondary aggregations into compound micelles both in aqueous and non-aqueous media. Upon increasing the solution temperature above LCST, micelles/compound micelles of PTyr- g -PEtOx GCC undergo further aggregation into higher order micellar agglomerates without any disruption of micellar structures as observed from DLS study. A hydrophobic dye (nile red) can easily be encapsulated into the hydrophobic PTyr core of the PTyr- g -PEtOx micelles in water, which remains stable without any release of the dye even when the temperature is increased above the LCST of the GCC.