We report the synthesis of poly(2-(N-(acryloyloxy)ethyl pyrrolidone)-poly(4-hydroxybutyl acrylate) (PNAEP85-PHBAx) diblock copolymer nano-objects via reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 4-hydroxybutyl acrylate (HBA) at 30 °C using a highly efficient one-pot protocol. Given the relatively low glass transition temperature of the PHBA block, these nano-objects required covalent stabilization prior to transmission electron microscopy (TEM) studies. This was achieved by core crosslinking using glutaraldehyde, which reacts with the pendent hydroxyl groups between neighboring PHBA chains to form acetal linkages. TEM analysis of the glutaraldehyde-fixed nano-objects confirmed that pure spheres, worms or vesicles could be obtained at 20 °C in acidic aqueous solution (pH 3) simply by varying the mean degree of polymerization (x) of the PHBA block. Aqueous electrophoresis, dynamic light scattering and TEM studies confirmed that raising the dispersion pH above the pKa of the terminal carboxylic acid group located on the PNAEP chains was sufficient to induce a vesicle-to-sphere transition. 1H NMR studies of linear PNAEP85-PHBAx diblock copolymer nano-objects indicated that this change in morphology was accompanied by an increase in the degree of hydration of the PHBA chains. A series of PNAEP85-PHBA340-375 worms formed free-standing gels in acidic aqueous solution owing to multiple inter-worm contacts. Rheological studies indicated that the critical temperature corresponding to the maximum worm gel viscosity, |η*|, could be tuned from 2 °C to 50 °C by adjusting the PHBA DP, with significantly stiffer worm gels being obtained for longer PHBA blocks at lower temperatures. This ability to tune the worm gel viscosity is likely to be important for their use as a wholly synthetic biocompatible matrix for either long-term 3D cell culture or stasis induction studies. However, this would require worm gels to be generated at neutral pH, rather than acidic pH.

Synthesis and aqueous solution properties of shape-shifting stimulus-responsive diblock copolymer nano-objects

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.