Phase transition and aggregation behaviour of an UCST-type copolymer poly(acrylamide-co-acrylonitrile) in water: effect of acrylonitrile content, concentration in solution, copolymer chain length and presence of electrolyte

Abstract

An UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization and its temperature-induced phase transition and aggregation behaviour studied by turbidimetry, static and dynamic light scattering, small angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM) measurements. The phase transition temperature was found to increase with increasing AN content in the copolymer, concentration of the solutions and copolymer chain length. A significant effect was observed onto the phase transition temperature by addition of different electrolytes into the copolymer solution. The copolymer chains were aggregated below the phase transition temperature and disaggregated above it. The size of the aggregates increases with increasing AN contents and concentration of the copolymer solutions below the phase transition temperature. The copolymer chains were expanded and weekly associated in solution above the phase transition temperature. A model is proposed to explain such association-aggregation behaviour of poly(AAm-co-AN) copolymers depending on AN contents and concentration of the copolymer solutions as a function of temperature.

Advances in thermo-responsive polymers exhibiting upper critical solution temperature (UCST)

“…RAFT polymerization was then performed using Aam and AN as monomer, AIBN as initiator and HBPO-DTBA as RAFT agent (Figure 7). In contrast to the report of Asadujjaman et al [34], the UCST of this novel hyperbranched polymer can be increased by decreasing the arm (chain) length due to its unique molecular topology [39]. Synthesis of an ABA type triblock copolymers using P(AAm-co-AN) as outer blocks or middle block and hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMMA) and poly (N,N-dimethylacrylamide-co-7-acryloyl-4-methylcoumarin) as middle block and outer block, respectively, have also been reported [40,41].…”

“…It was proposed that by changing the molar ratio of hydrophobic AN in Poly(AAm-co-AN), the UCST of polymer can be tuned easily ( Figure 4) [33]. Later, Asadujjaman et al [34] suggested that Poly(AAm-co-AN) with AN content between 0.086 to 0.221 only demonstrate UCST behavior with cloud point ranging from 5.5 to 56.5°C at 1 mg/ml concentration in water. This report suggested that the phase transition temperature (T pt ) increases with increase in AN content in the copolymer, increasing polymer concentration and polymer chain length and by addition of 300 mM Na 2 SO 4 in solution.…”

Transformer Hydrogels: A Review

“…Above the UCST, there is rapid dissociation of hydrogen bonds and AAc‐AAm units, often referred to as a “zipper effect” resulting in solubilization of the individual units and dramatic swelling . Molecular chain modifications and copolymerization can also affect the stability and the swelling characteristics of these UCST hydrogels . In addition, ionic interactions can also be utilized to drive UCST behavior as in polybetaines.…”

Synthesis of Thermoresponsive Copolymers with Tunable UCST‐Type Phase Transition Using Aqueous Photo‐RAFT Polymerization

“…[ 11–21 ] The non‐ionic polymers have attracted a great deal of attention due to their insensitivity to salts, which make them more attractive for applications in physiological environment. [ 22–24 ] During the last decade, efforts have been focused toward developing novel water‐soluble copolymers exhibiting UCST behavior by copolymerizing H‐donor monomers ( N ‐acryloyl glycinamide [ 11–16 ] or acrylamide [ 15,17–21,25 ] ) and H‐acceptor monomers (acrylonitrile, [ 11,15,18,19,21,25,26 ] styrene, [ 15,17 ] and butyl acrylate [ 15 ] ). Such (co)polymers have been mainly prepared using free radical polymerization [ 11,14–17,26 ] and by thermally initiated controlled radical polymerization such as atom transfer radical polymerization [ 13 ] and reversible addition fragmentation chain transfer (RAFT) [ 11,12,16–19,25 ] The impacts of various parameters on the UCST phase transition, including salts, pH, molecular weight, molecular weight distribution, and chemical composition, have been well evaluated.…”

“…Such (co)polymers have been mainly prepared using free radical polymerization [ 11,14–17,26 ] and by thermally initiated controlled radical polymerization such as atom transfer radical polymerization [ 13 ] and reversible addition fragmentation chain transfer (RAFT) [ 11,12,16–19,25 ] The impacts of various parameters on the UCST phase transition, including salts, pH, molecular weight, molecular weight distribution, and chemical composition, have been well evaluated. [ 7–9,25,27 ] However, such studies were carried out at low polymer concentrations (below 5 wt%). This could induce, an unintentional confusion between the UCST and the apparent cloud point temperature ( T CP ), which refers to the temperature at which the phase transition occurs depending on the investigated concentration level.…”