“Inverse Polyampholyte” Hydrogels from Double-Cationic Hydrogels: Synthesis by RAFT Polymerization and Characterization

Abstract

We present two novel, homologous, pyridinebased monomers, 2-(pyridin-2-yl)ethyl methacrylate (PyEMA) and (pyridin-2-yl)methyl methacrylate (PyMMA), which, despite their structural similarity, the former can be readily thermolyzed to methacrylic acid, while the latter remains intact under the same conditions. This was most dramatically demonstrated in the present work, where PyEMA and PyMMA were randomly terpolymerized with a dimethacrylate cross-linker using reversible addition−fragmentation chain transfer polymerization to yield weakly double-cationic polyelectrolyte hydrogels of three different compositions which, upon thermal treatment, they were readily converted to polyampholyte hydrogels. While the parent double-cationic polyelectrolyte hydrogels exhibited a swelling response only to low-pH conditions, the daughter polyampholyte hydrogels presented swelling responses to both high-and low-pH conditions. Owing to the relative values of the effective pK a 's of the weakly acidic and weakly basic units, with the latter being lower than the former ("inverse polyampholyte" behavior), the swelling profiles of the daughter hydrogels were insensitive to polyampholyte composition.

Symmetrical polymer systems prepared using a degradable bifunctional atom transfer radical polymerization initiator: Synthesis, characterization, and cleavage

“…This will enable the selective alkaline hydrolysis of the residue from the cleavable linkers, without affecting the ester groups of the monomer repeating units. This selectivity in the alkaline hydrolysis of the 2‐(pyridin‐2‐yl)ethanol mono‐ and di‐esters relative to common methacrylate monomers has already been demonstrated in our previous studies on polymers bearing PyEMA monomer repeating units and PyDMA cross‐linker units…”

“…We recently imported this to polymer chemistry, to protect methacrylic acid (MAA), transforming it to 2‐(pyridin‐2‐yl)ethyl methacrylate (PyEMA), polymerizing it, and then readily removing the protecting group in the form of 2‐vinylpyridine, either by treatment with sodium hydroxide solution at RT or by thermolysis in the temperature range between 110 °C and 160 °C under neutral conditions in the bulk or in solution . Furthermore, we showed that the PyEMA units in terpolymers with 2‐tetrahydropyranyl methacrylate (THPMA) and benzyl methacrylate (BzMA) are preserved under acidic hydrolysis conditions where the THPMA units are readily converted to MAA units . Additionally, we demonstrated that the polymer of the lower homologous group, the (pyridin‐2‐yl)methyl group, formed a much more stable MAA ester, (pyridin‐2‐yl)methyl methacrylate (PyMMA) .…”

“…35 Additionally, we demonstrated that the polymer of the lower homologous group, the (pyridin-2-yl)methyl group, formed a much more stable MAA ester, (pyridin-2-yl)methyl methacrylate (PyMMA). 36,37 with its units requiring a much higher thermolysis temperature (around 330 8C), and being amenable to only partial alkaline hydrolysis (44% after 2 weeks of hydrolysis, whereas the alkaline hydrolysis of the PyEMA units is complete within 2 h). Most recently, we developed a dimethacryate analogue of the PyEMA monomer, 2,6-pyridinediethanol dimethacrylate (PyDMA), which acts as a cross-linker/branching agent, and we proved that the polymeric products of PyDMA, hyperbranched polymers or polymer networks, readily undergo thermolysis or hydrolysis under alkaline conditions, but remain stable under acidic hydrolysis conditions.…”

In situ silver nanoparticle formation embedded into a photopolymerized hydrogel with biocide properties

“…Hydrogels may be synthesized via several different ways such as thermal- [25], redox- [26], RAFT- [27,28] and photopolymerization [29]. This last method that corresponds to a photoinitiated radical polymerization of multifunctional monomers that produce highly crosslinked polymers, has several advantages over conventional ones like spatial and temporal control, fast curing and reaction rates at room temperature, solvent-free formulation, among others.…”

UCST behavior of polyampholytes based on stoichiometric RAFT copolymerization of cationic and anionic monomers

“…More recently, poly(oligoethylene glycol (meth)acrylate)s, [3][4][5][6][7] poly(2-oxazoline)s, [8][9][10][11][12][13] poly(vinyl ether)s 14 and polypeptides 15,16 have also been widely studied and have found various applications as smart materials. 38 The development of polyampholytes based on cationic and anionic monomers with UCST behavior is extremely challenging as both monomers need to be incorporated in stoichiometric amounts. Compared with polymers that undergo an LCST transition, such polymers exhibiting UCST behavior in aqueous solution have been much less documented as it is much more challenging to achieve this behavior in aqueous solutions requiring strong interpolymer attraction in combination with high hydrophilicity.…”