Recently, a family of upper critical solution temperature (UCST) block copolymer micelles (BCMs) have been developed in our group. Such micelles can be included in hydrogen-bonded layer-by-layer (LbL) films and show potential as temperature-responsive containers for applications such as drug delivery and soft actuation. However, methods to control film response at the deposition step are poorly understood. In this work, we study the assembly of UCST BCMs, which are composed of poly(acrylamide-<i>co</i>-acrylonitrile) cores and polyvinylpyrrolidone (PVP) coronae, within LbL films <i>via</i> hydrogen bonding with poly(methacrylic acid) (PMAA). By monitoring dry film thickness and film swelling with spectroscopic ellipsometry, film internal structure with neutron reflectometry, and enthalpy of binding of PMAA with PVP micellar coronae by isothermal titration calorimetry, we identified the main factors that contribute to preserving temperature responsiveness of UCST cores of assembled BCMs. In strongly acidic deposition conditions, BCM/PMAA assemblies display a crumpled micellar morphology and low swelling amplitude. By studying the enthalpy of binding of PMAA with the core and corona blocks of UCST-responsive micelles, we find that in strongly acidic conditions PMAA interacts with both blocks of UCST polymers. Therefore, selective binding of PMAA with corona blocks and presence of weak charge on PMAA, which can be endowed by increasing pH, were critical for stabilizing micellar structures in LbL assemblies, giving robust micelle morphology, while simultaneously preserving their temperature-triggered response. Neutron reflectometry studies indicated that sufficient stratification remained within the film to permit reversible swelling-deswelling transitions. Using this temperature-responsive swelling behavior to uptake and release model drugs from micellar layers in response to a temperature stimulus is discussed.

Controlling functionality of layer-by-layer assembled upper critical solution temperature micelles

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.