A Single Thermoresponsive Diblock Copolymer Can Form Spheres, Worms or Vesicles in Aqueous Solution

Alessandro Ianiro,Steven P Armes,Matthew J Derry,Remco Tuinier,Liam P D Ratcliffe

doi:10.1002/ange.201909124

Abstract

AbstractIt is well‐known that the self‐assembly of AB diblock copolymers in solution can produce various morphologies depending on the relative volume fraction of each block. Recently, polymerization‐induced self‐assembly (PISA) has become widely recognized as a powerful platform technology for the rational design and efficient synthesis of a wide range of block copolymer nano‐objects. In this study, PISA is used to prepare a new thermoresponsive poly(N‐(2‐hydroxypropyl) methacrylamide)‐poly(2‐hydroxypropyl methacrylate) [PHPMAC‐PHPMA] diblock copolymer. Remarkably, TEM, rheology and SAXS studies indicate that a single copolymer composition can form well‐defined spheres (4 °C), worms (22 °C) or vesicles (50 °C) in aqueous solution. Given that the two monomer repeat units have almost identical chemical structures, this system is particularly well‐suited to theoretical analysis. Self‐consistent mean field theory suggests this rich self‐assembly behavior is the result of the greater degree of hydration of the PHPMA block at lower temperature, which is in agreement with variable temperature 1H NMR studies.

Highlights

Block copolymer self-assembly in solution has been known for more than fifty years.[1]
For the self-assembly of amphiphilic AB diblock copolymer chains in aqueous solution, spheres,[2c] worms[2f] or vesicles[4] are by far the most common copolymer morphologies. Such nano-objects are readily accessible via polymerizationinduced self-assembly (PISA), which can be conducted in concentrated aqueous media.[5]. This is largely owing to the development of controlled radical polymerisation techniques such as reversible addition-fragmentation chain transfer (RAFT) polymerization,[6] which has enabled the convenient synthesis of a wide range of well-defined functional block copolymers.[7]
The reaction time was deliberately restricted to 4 h (41 % conversion by 1H NMR) to ensure high chain-end fidelity. This water-soluble precursor was utilized to prepare a series of PHPMAC41-PHPMAy diblock copolymer nano-objects at 10 % w/w solids via RAFT aqueous dispersion polymerization of HPMA at 70 8C, see Figure 1 and Figure S2

Summary

Introduction

Block copolymer self-assembly in solution has been known for more than fifty years.[1]. Phologies have been reported, including spheres, worms, rods, vesicles, lamellar platelets, disks, toroids, stomatocytes and framboidal vesicles.[2] Potential applications include drug delivery, nanoencapsulation, membranes, biocompatible hydrogels, chemotaxis and diesel soot dispersion in engine oils.[3] For the self-assembly of amphiphilic AB diblock copolymer chains in aqueous solution, spheres,[2c] worms[2f] or vesicles[4] are by far the most common copolymer morphologies. Such nano-objects are readily accessible via polymerizationinduced self-assembly (PISA), which can be conducted in concentrated aqueous media.[5] This is largely owing to the development of controlled radical polymerisation techniques such as reversible addition-fragmentation chain transfer (RAFT) polymerization,[6] which has enabled the convenient synthesis of a wide range of well-defined functional block copolymers.[7]. Subtle difference in chemical structure (see Figure 1) between these two types of monomer repeat units aids theoretical analysis of this system using self-consistent mean field theory,[15] because it ensures very similar segment volumes for these two components when using a lattice model

Results and Discussion

Conclusion

Conflict of interest