Dynamic control of volume phase transitions of poly(N‐isopropylacrylamide) based microgels in water using hydrazide‐aldehyde chemistry

Abstract

We demonstrate that the volume phase transition temperature (VPTT) of copolymer microgel particles made from N‐isopropylacrylamide (NIPAm) and methacryloyl hydrazide (MH) can be tailored in a reversible manner upon the reaction of the hydrazide functional groups with aldehydes. The microgels were synthesized by precipitation polymerization in water. Due to the water‐soluble nature of the MH monomer, the VPTT at which the microgel particles contract shifts to higher values by increasing the incorporated amounts of methacryloyl hydrazide from 0 to 5.0 mol %. The VPTT of the copolymer microgel dispersions in water can be fine‐tuned upon addition of hydrophobic/hydrophilic aldehydes, which react with the hydrazide moiety to produce the hydrazone analogue. This hydrazone formation is reversible, which allows for flexible, dynamic control of the thermo‐responsive behavior of the microgels. The ability to “switch” the VPTT was demonstrated by exposing hydrophilic streptomycin sulfate salt incubated microgel particles to an excess of a hydrophobic aldehyde, that is benzaldehyde. The temperature at which these microgels contracted in size upon heating was markedly lowered in these aldehyde exchange experiments. Transformation into benzaldehyde hydrazone derivatives led to assembly of the microgel particles into small colloidal clusters at elevated temperatures. This control of supracolloidal cluster formation was also demonstrated with polystyrene particles which had a hydrazide functionalised microgel shell. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1745–1754

A ‘catch-and-release’ receptor for the cholera toxin

“…We chose to construct our receptor on a poly(Nisopropylacrylamide) (poly(NIPAm)) scaffold, a class of polymer well known for its ability to reversibly desolvate upon increases in solution temperature. 21 NIPAm was copolymerised with tert-butyl 2-methacryloylhydrazine-1-carboxylate (M1) (Scheme 1), which was prepared via hydrazinolysis of methacrylic anhydride, 22 and subsequent BOC-protection of hydrazide units. RAFT polymerisation afforded a copolymer with a degree of polymerisation of approximately 99, displaying approximately 21 protected acylhydrazide functionalities as estimated using 1 H NMR spectroscopy.…”

Dynamic covalent polymers

“…In another example, Chen et al described a microgel based on a PNIPAM polymer that also incorporates a fraction of pendant hydrazides groups in its polymer backbone . Upon reaction of the hydrazide functional pendant groups with aldehydes of different hydrophilicity, the temperature at which the microgel reversible turns into colloids could be tailored.…”

Towards being genuinely smart: ‘isothermally-responsive’ polymers as versatile, programmable scaffolds for biologically-adaptable materials

“…104 Guo et al prepared an amidine-based polymer which underwent a hydrophilic-hydrophilic transition using CO 2 as a stimulus. Importantly, the microgel solubility, and hence volume phase transition, could be modulated by careful selection of aldehydes with varying hydrophilicities.…”