Self-Assembly of Linear Amphiphilic Pentablock Terpolymer PAAx-PS48-PEO46-PS48-PAAxin Dilute Aqueous Solution.

Chao Lv,Junting Xu,Binyang Du,Jingjing Nie,Kun An,Jia Gao

doi:10.3390/polym12102183

Abstract

A series of linear amphiphilic pentablock terpolymer PAAx-b-PS48-b-PEO46-b-PS48-b-PAAx (AxS48O46S48Ax) with various lengths x of the PAA block (x = 15, 40, 60, and 90) were synthesized via a two-step atom transfer radical polymerization (ATRP) using Br-poly(ethylene oxide)-Br (Br-PEO46-Br) as the macroinitiator, styrene (St) as the first monomer, and tert-butyl acrylate (tBA) as the second monomer, followed with the hydrolysis of PtBA blocks. The AxS48O46S48Ax pentablock terpolymers formed micelles in dilute aqueous solution, of which the morphologies were dependent on the length x of the PAA block. Cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and zeta potential measurement were employed to investigate the morphologies, chain structures, size, and size distribution of the obtained micelles. The morphology of AxS48O46S48Ax micelles changed from spherical vesicles with ordered porous membranes to long double nanotubes, then to long nanotubes with inner modulated nanotubes or short nanotubes, and finally, to spherical micelles or large compound vesicles with spherical micelles inside when x increased from 15 to 90. The hydrophobic PS blocks formed the walls of vesicles and nanotubes as well as the core of spherical micelles. The hydrophilic PEO and PAA block chains were located on the surfaces of vesicle membranes, nanotubes, and spherical micelles. The PAA block chains were partially ionized, leading to the negative zeta potential of AxS48O46S48Ax micelles in dilute aqueous solutions.

Highlights

Amphiphilic block copolymers, with hydrophilic and hydrophobic segments connected by covalent bonds, can self-assemble into micelles with various morphologies and structures in selective solvents [1,2,3,4]
Ax S48 O46 S48 Ax pentablock terpolymers with different lengths x of PAA blocks were synthesized via a two-step atom transfer radical polymerization (ATRP) process with Br-PEO46 -Br as the macroinitiator, St as the first monomer, and tert-butyl acrylate (tBA) as the second monomer, followed with the hydrolysis of PtBA blocks, as shown in Scheme 1
The characteristic peak of –C(CH3 )3 with chemical shift of ca. 1.35 ppm, which can be clearly observed for Tx S48 O46 S48 Tx (Figure 1a), completely disappeared for Ax S48 O46 S48 Ax (Figure 1b), indicating that the PtBA blocks were completely hydrolyzed and turned into PAA blocks

Summary

Introduction

Amphiphilic block copolymers, with hydrophilic and hydrophobic segments connected by covalent bonds, can self-assemble into micelles with various morphologies and structures in selective solvents [1,2,3,4]. The self-assembly of block copolymers in selective solvents has been extensively studied experimentally [15,16] and theoretically [17,18,19,20]. The morphologies and structures of block copolymer micelles are strongly dependent on the monomer type, composition, and molecular weight of block copolymers as well as the use of selective solvents. Spherical and rod-like micelles, vesicles, large compound micelles, micelles with octopi, jellyfish, and bamboo cage shapes as well as spindle worm-like micelles have been reported for AB diblock copolymer and ABC triblock terpolymers in various selective solvents like aqueous solution, DMF, methanol-water mixture, and THF-water mixture [21,22,23,24,25].

Methods

Results

Conclusion