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Shape-shifting thermoreversible diblock copolymer nano-objects via RAFT aqueous dispersion polymerization of 4-hydroxybutyl acrylate

DOI: 10.1039/D1SC05022B DOI Help

Authors: Oliver J. Deane (University of Sheffield) , James Jennings (University of Sheffield) , Steven P. Armes (University of Sheffield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemical Science , VOL 268

State: Published (Approved)
Published: October 2021
Diamond Proposal Number(s): 27967

Open Access Open Access

Abstract: 2-Hydroxypropyl methacrylate (HPMA) is a useful model monomer for understanding aqueous dispersion polymerization. 4-Hydroxybutyl acrylate (HBA) is an isomer of HPMA: it has appreciably higher aqueous solubility so its homopolymer is more weakly hydrophobic. Moreover, PHBA possesses a significantly lower glass transition temperature than PHPMA, which ensures greater chain mobility. The reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HBA using a poly(ethylene glycol) (PEG113) precursor at 30 °C produces PEG113–PHBA200–700 diblock copolymer nano-objects. Using glutaraldehyde to crosslink the PHBA chains allows TEM studies, which reveal the formation of spheres, worms or vesicles under appropriate conditions. Interestingly, the partially hydrated highly mobile PHBA block enabled linear PEG113–PHBAx spheres, worms or vesicles to be reconstituted from freeze-dried powders on addition of water at 20 °C. Moreover, variable temperature 1H NMR studies indicated that the apparent degree of hydration of the PHBA block increases from 5% to 80% on heating from 0 °C to 60 °C indicating uniform plasticization. In contrast, the PHPMAx chains within PEG113–PHPMAx nano-objects become dehydrated on raising the temperature: this qualitative difference is highly counter-intuitive given that PHBA and PHPMA are isomers. The greater (partial) hydration of the PHBA block at higher temperature drives the morphological evolution of PEG113–PHBA260 spheres to form worms or vesicles, as judged by oscillatory rheology, dynamic light scattering, small-angle X-ray scattering and TEM studies. Finally, a variable temperature phase diagram is constructed for 15% w/w aqueous dispersions of eight PEG113–PHBA200–700 diblock copolymers. Notably, PEG113–PHBA350 can switch reversibly from spheres to worms to vesicles to lamellae during a thermal cycle.

Subject Areas: Chemistry, Materials

Instruments: I22-Small angle scattering & Diffraction

Added On: 12/10/2021 09:50


Discipline Tags:

Soft condensed matter physics Chemistry Materials Science Organic Chemistry Polymer Science

Technical Tags:

Scattering Small Angle X-ray Scattering (SAXS)