Dielectric analysis of the upper critical solution temperature behaviour of a poly(acrylamide-co-acrylonitrile) copolymer system in water

Abstract

A copolymer consisting of acrylamide (AAm) and acrylonitrile (AN) in aqueous solution was investigated using broadband dielectric spectroscopy at frequencies between 10 Hz and 10 Hz in the temperature range from 2 °C to 60 °C. This system shows an UCST phase behavior. The phase transition and aggregation behavior is monitored by both the temperature and frequency dependence of the complex conductivity σ*(f, T), where the AN fraction and the concentration of the solution were varied. Additionally, the dielectric data are compared with the results obtained from dynamic light scattering measurements. The temperature dependence of the DC conductivity (σ) of the copolymer solution is monitored and the phase transition temperature (PTT) of the poly(AAm-co-AN) copolymer is deduced from a change in the T-dependence of the DC conductivity. The change in σ can be explained by decreased effective charge carrier mobility and a reduction of the effective charge number density at temperatures below the phase transition temperature of the poly(AAm-co-AN) solution. A pronounced interfacial polarization effect on the frequency dependence of the real part of the conductivity (σ') is observed at temperatures below the phase transition temperature. The charge carriers are blocked at the formed aggregates giving rise to this interfacial polarization. The dependence of the interfacial polarization on the acrylonitrile fraction in the copolymer and the concentration of the solution is studied in detail and conclusions concerning the internal structures of the copolymer aggregates are drawn.

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

“… The obtained poly(AM‐ co ‐AN) copolymer exhibited UCST properties with tunable phase transition temperature ( T CP ) in pure water as shown also by our group . The T CP was varied between 5.5 °C and 56.5 °C by tuning the hydrophilic–hydrophobic balance . Moreover, the T CP decreased by ~10 °C by dilution of the polymer concentrations from 50 to 1.0 mg∙mL −1 .…”

“…Agarwal and coworkers obtained a UCST‐copolymer based on hydrophilic acrylamide (AM) and hydroneutral acrylonitrile (AN). The obtained poly(AM‐ co ‐AN) copolymer exhibited UCST properties with tunable phase transition temperature ( T CP ) in pure water as shown also by our group . The T CP was varied between 5.5 °C and 56.5 °C by tuning the hydrophilic–hydrophobic balance .…”

Upper critical solution temperature thermo-responsive polymer brushes and a mechanism for controlled cell attachment

“…Nevertheless, the changes in surface properties around the UCST clearly affected cell adhesion, and the extension of this promising methodology to other cell types is now ongoing in our laboratories. The possibility to modulate further UCST-type changes not only by monomer content but by polymer chain length 35 and/or grafting density at surfaces, as has been demonstrated for LCST-type polymers, 36 offers further means by which cell attachment and behaviour might be controlled.…”

The crucial role of macromolecular engineering, drug encapsulation and dilution on the thermoresponsiveness of UCST diblock copolymer nanoparticles used for hyperthermia

“…In terms of polymer synthesis, P(AAm-co-AN) can be easily synthesized by free-radical polymerization [19][20][21] or reversible deactivation radical polymerization techniques such as reversible addition fragmentation chain transfer (RAFT) polymerization. [22][23][24][25][26] The copolymer obtained by free-radical polymerization has been grafted with poly(ethylene glycol) (PEG) on the acrylamide monomers to formulate thermoresponsive nanoparticles efficiently responding to mild-hyperthermia for in vivo tumor treatment. [27] Here, we design a different synthetic route to yield a well-defined, amphiphilic block copolymer.…”