Fluorescent Labeling Method Re-Evaluates the Intriguing Thermoresponsive Behavior of Poly(acrylamide-co-acrylonitrile)s with Upper Critical Solution Temperatures

Abstract

We investigated the thermoresponsive behavior of poly­(acrylamide-co-acrylonitrile) (poly­(AAm-co-AN)) with an upper critical solution temperature (UCST) in water to apply this polymer in cosmetic products that can be easily removed by washing with hot water. Six kinds of poly­(AAm-co-AN) polymers were synthesized, and those containing higher contents of AN units showed higher UCSTs in water. The amount of AN units in the resulting copolymer was controlled only by adding AN immediately prior to the polymerization to prevent its loss due to volatilization. We also analyzed the UCST behavior of poly­(AAm-co-AN) by fluorometry by labeling the polymer with an environment-sensitive fluorophore. The fluorescence spectra, fluorescence quenching titration results, and time-resolved fluorescence anisotropy measurements revealed that poly­(AAm-co-AN) loosely aggregated below the UCST, and the dipole–dipole interaction between the cyano groups in AN units and the hydrogen bonds between the amide groups in the AAm units were responsible for the cross-linking of the aggregates.

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

“…Similar behavior trends of poly(AAm‐ co ‐AN) in water were observed by others groups. [ 15,21 ] However, it is not possible to directly compare our results with those previously reported because of the difference of copolymer concentrations.…”

“…The latter contain H‐donor and H‐acceptor sites, which are able to form intra‐molecular reversible hydrogen bonds (globule conformation below UCST) and inter‐molecular bonds with water (coil conformation above UCST). [ 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 ] ).…”

“…[ 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.…”

“…Control of the molar mass is an important parameter when investigating the UCST phase transition as it was reported recently. [ 16,17,21 ] The molar fractions of AN inserted in the copolymers () were estimated from 1 H NMR of the final reaction media. Small increase of compared to the fractions of AN () initially present in the feed prior to RAFT polymerization was observed due to the relatively high reactivity of AN compared to AAm.…”

A versatile UCST-type composite microsphere for image-guided chemoembolization and photothermal therapy against liver cancer

“…The solubility as well as the drug release rate of the UCST polymer increase substantially when the temperature exceeds a certain threshold that facilitates hyperthermia and chemotherapy to function simultaneously, which may interact synergistically to produce a remarkable enhancement. [22][23][24][25] In this work, a novel doxorubicin loaded versatile composite microsphere with UCST properties and encapsulated polydopamine coated superparamagnetic iron oxide nanoparticles (SPION@PDA) was prepared for simultaneous chemoembolization and photothermal therapy. Comprehensive characterization studies were performed to fully investigate the physicochemical and mechanical properties of the prepared microsphere.…”