Non‐Ionic Homo‐ and Copolymers with H‐Donor and H‐Acceptor Units with an UCST in Water

Abstract

A well‐studied example of a thermoresponsive polymer is PNiPAAm, which exhibits a sharp coil‐to‐globule transition in water at its LCST. A study relating to the missing counterpart of LCST polymers is presented: N‐acryloylglycinamide (NAGA) homopolymer and copolymers from NAGA and N‐acetylacrylamide (NAcAAm) that show a sharp UCST (where the sharpness depends on the composition). The polymers were synthesized by free‐radical copolymerization and the copolymerization parameters were determined by the method of Kelen‐Tüdös. The UCST was investigated by turbidimetry, regarding the influence of the copolymer composition, the polymer concentration and the addition of electrolytes. magnified image

Thermo-Responsive Hydrogels for Stimuli-Responsive Membranes

“…Early work on hydrogels undergoing volume phase transitions surmised that the transition was driven by ionized pendant groups in the network and discrete or continuous change was determined by the degree of ionization [21,30,42]. Ionization of a gel was induced by copolymerization or hydrolysis.…”

“…Other aspects to consider which will be discussed in following sections are ionic dissociation of carboxyl groups and hydrophobic composition of the polymer chains. [30].…”

“…Thermophilic hydrogels typically maintain a collapsed conformation at temperatures below their VPTT while thermophobic hydrogels are able to swell at lower temperatures. The volume-phase transition may be reversible but not in all cases and hysteresis is frequently experienced [27][28][29][30][31].…”

Tuning the critical solution temperature of polymers by copolymerization

“…The CST has been observed then to depend either monotonically [12][13][14][15][16][17][18][19][20] or nonmonotonically 15,16,18,19 on the degree of copolymerization. In the typical scenario of a lower CST (LCST) in aqueous solvents, monotonic trends are often qualitatively explained by the degree of hydrophobicity/philicity of the copolymerizing monomers.…”

Well-Defined Thermoresponsive Copolymers with Tunable LCST and UCST in Water

“…On the contrary, polymers that exhibit upper critical solution temperature (UCST) behavior become more hydrophilic in water with increasing temperature. [12][13][14][15] Such thermoresponsive polymers featuring a LCST and a UCST in water are expected to find applications in nanotechnology and biotechnology. 16,17 Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), 18 which displays a LCST in water around 40 °C, has been the most studied thermoresponsive polymer targeting biological applications.…”