2,6‐Diaminopyridine and Acrylamide‐Based Copolymers with Upper Critical Solution Temperature‐type Behavior in Aqueous Solution

Abstract

A novel copolymer based on supramolecular motif 2,6-diaminopyridine and water-soluble acrylamide, poly[N-(6-acetamidopyridin-2-yl) acrylamide-co-acrylamide], was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization with various monomer compositions. The thermoresponsive behavior of the copolymers was studied by turbidimetry and dynamic light scattering (DLS). The obtained copolymers showed an upper critical solution temperature (UCST)-type phase transition behavior in water and electrolyte solution. The phase transition temperature was found to increase with decreasing amount of acrylamide in the copolymer and increasing concentration of the solution. Furthermore, the phase transition temperature varied in aqueous solutions of electrolytes according to the nature and concentration of the electrolyte in accordance with the Hoffmeister series. A dramatic solvent isotope effect on the transition temperature was observed in this study, as the transition temperature was almost 10-12 C higher in D 2 O than in H 2 O at the same concentration and acrylamide composition. The size of the aggregates below the transition temperature was larger in D 2 O compared to that in H 2 O that can be explained by deuterium isotope effect. The thermoresponsive behavior of the copolymers was also investigated in different cell medium and found to be exhibited UCST-type phase transition behavior in different cell medium. Such behavior of the copolymers can be useful in many applications including biomedical, microfluidics, optical materials, and in drug delivery.

The Design of Sulfobetaine Polymers with Thermoresponsiveness under Physiological Salt Conditions

“…Compared to LCST polymers, UCST polymers have not been studied as much. However, recent attention has been given to UCST polymers that are induced by hydrogen bonding interactions 9. Some of these polymers are also designed for further usage in biological applications 10…”

Aqueous Synthesis of Upper Critical Solution Temperature and Lower Critical Solution Temperature Copolymers through Combination of Hydrogen‐Donors and Hydrogen‐Acceptors

“…TRPs normally behave differently in water (H 2 O) and heavy water (D 2 O), because deuterium forms more stable H‐bond than its isotope. [ 30,47 ] As shown in Figure 3e,f, the T cp of a U3 solution is 32 °C in H 2 O and 39 °C in D 2 O, while the T cp of a L2 solution is 34 °C in H 2 O and 19 °C in D 2 O. These results could be related to the AAc–NVP interaction in heavy water.…”

“…[ 27 ] Homopolymers of acrylamide (AAm) are freely soluble in water, but copolymers of AAm with hydrophobic comonomers such as acrylonitrile, azobenzene, diaminopyridine, or styrene can have a UCST in aqueous solutions. [ 28–31 ] In contrast, homopolymers of dimethyl acrylamide (DMA) is also water‐soluble, but copolymer of DMA with hydrophobic monomers, such as styrene or phenylacrylamide, exhibit LCST behavior in water. [ 32,33 ] These previous results demonstrate the great potential of fabricating TRPs from “non‐responsive” monomers.…”

“…Its UCST‐type transition becomes broader and its T cp is decreased gradually upon dilution from 20 to 1.0 g L −1 , which can be attributed to the delayed interchain H‐bonding at diluted concentration and also observed in other H‐bonded UCST polymers. [ 30,42 ] As for L2, its LCST transition also become less sharp with lower polymer concentration, due to the retarded chain complexation as well. However, the T cp – c polymer curve of the LCST copolymer shows concave shape with a minimum at 10 g L −1 , neither similar with the monotonous behavior of their UCST cousins nor with the nearly‐flat phase diagram of PNIPAM.…”

Small dop of comonomer, giant shift of cloud point: Thermo‐responsive behavior and mechanism of poly(methylacrylamide) copolymers with an upper critical solution temperature

“…A NAGA monomer contains two H-donors and two H-acceptors, capable of forming double H-bonds, so that the polymer chains would be associated upon cooling and exhibit a UCST behavior in water. [21] Polyacrylamide (PAM) is water-soluble, but can also be turned into a UCST polymer through copolymerization with hydrophobic comonomers like acrylonitrile, [22][23][24][25][26] styrene, [27] 2,6-diaminopyridine [28] or azobenzene, [29] where the comonomers can strengthen the polymerpolymer H-bonding. However, the preparation of these UCST polymers usually require the synthesis of functional monomers, such as NAGA, or the use of organic solvents to dissolve the hydrophobic comonomer, such as PAM copolymers, which limits their practical applications.…”