Swelling Transitions in Layer-by-Layer Assemblies of UCST Block Copolymer Micelles

Abstract

An upper critical solution temperature (UCST) block copolymer, poly­(acrylamide-co-acrylonitrile)-b-polyvinyl­pyrrolidone (P­(AAm-co-AN)-b-PVP), was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, assembled in solution, and deposited within functional layer-by-layer (LbL) temperature-responsive films. In aqueous solutions, the polymer formed well-defined block copolymer micelles (BCMs) at ambient temperature and exhibited a reversible micelle–unimer transition within an ∼40–50 °C temperature range in a wide range of pH and ionic strengths. Temperature-induced dissociation of BCMs to unimers was completely suppressed, however, when BCMs were assembled with tannic acid (TA) within LbL films. Instead, reversible changes in micellar sizes and film swelling occurred as a result of UCST-driven uptake/release of water within/from the micellar cores. The solution pH modulated strength of hydrogen bonding between TA and PVP in the micellar corona, thus strongly affecting film growth, micelle morphology, and film swelling. Spherical micellar morphology and high film swelling degrees were observed with films at neutral pH values, where hydrogen bonding was counteracted by the negative charge of partially ionized TA. In contrast, strong hydrogen bonding and absence of charge in TA caused crumpling of BCMs and reduced the film swelling degree in acidic solutions. Film swelling was also dependent on number of assembled micellar layers, with thicker films exhibiting larger swelling amplitudes and sharper temperature transitions. The LbL assemblies were stable in phosphate buffer saline up to pH 7.5 at 50 °C and preserved their response after 55 heating/cooling cycles. The robustness of the temperature transitions in these films taken together with their occurrence in an aqueous environment in a wide range of pH and ionic strengths makes these films potentially useful for controlling responses of soft interfaces in biological environments.

Thermoresponsive properties of poly(acrylamide-co-acrylonitrile)-based diblock copolymers synthesized (by PISA) in water

“…3 Indeed, the latter was largely used to engineer thermoresponsive/stimuli-responsive block copolymer systems for drug delivery purposes, cancer theranostics/chemotherapy and photoacoustic imaging. [40][41][42][43][44][45][46][47][48][49][50][51][52] It is generally obtained by radical copolymerization of acrylamide and acrylonitrile in organic solvents, mainly in dimethylsulfoxide (DMSO). Both free radical polymerization (FRP) and reversible deactivation radical polymerization (RDRP) [53][54][55][56][57][58] mechanisms -in particular the reversible addition fragmentation chain transfer (RAFT) -have been used.…”

Constrained thermoresponsive polymers – new insights into fundamentals and applications

“…Recently, the discovery of novel UCST polymers has led to advancements in thermoresponsive block copolymers [ 331 – 332 ]. Zhang et al [ 333 ], Käfer et al [ 334 ], and Zhou et al [ 335 ] succeeded in embedding the nonionic UCST-type copolymer P(AAm- co -AN) into dual thermoresponsive (UCST–LCST) systems, which were complemented either by a PDMAEMA, PEG or PNIPAAm LCST block.…”

Thermo‐Responsive Polymer Capsules in Real‐Time One‐Step RT‐PCR for Highly Multiplex RNA Analysis

“…A solid UCST polymer becomes a liquid above a critical temperature ( T c ). [ 1,12 ] Well‐characterized hydrophilic UCST polymers, such as gelatin and agarose, were selected to support the biochemical enzyme reactions of RT and PCR. As mentioned, the first required specification of the polymer capsule is to keep the PCR primers from the RT reaction.…”