Layer-by-Layer Assembly of Two Temperature-Responsive Homopolymers at Neutral pH and the Temperature-Dependent Solubility of the Multilayer Film

Abstract

We fabricated a layer-by-layer (LbL) film of temperature-responsive homopolymers at neutral pH and studied its temperature-dependent solubility. We first measured the cloud point of mixed solutions of temperature-responsive polymers. The significant decrease of cloud point suggested that the intermolecular interaction between two polymer chains of different kinds was stronger than that between two polymer chains of the same kind. Strong intermolecular interaction between two polymer chains of different kinds is a prerequisite for LbL assembly. On the basis of the decrease of cloud point of mixed solutions of temperature-responsive homopolymers, we selected poly(N-vinylcaprolactam) (PVCL) and poly(2-hydroxypropyl acrylate) (PHPA) for LbL assembly. LbL films of the two polymers were fabricated at neutral pH at a constant temperature. When the film was immersed in purified water at a temperature lower than the assembly temperature, it can be partially dissolved with a diffusion-limited dissolution process. The temperature-responsive solubility of the LbL film is closely connected to the phase behavior of mixed solutions of the two polymers. Additionally, as compared to multilayer films of neutral polymers and poly(carboxylic acid)s, the PVCL/PHPA multilayer film is relatively stable when it was immersed in buffer solutions near physiological pH at the assembly temperature. Such LbL films with temperature-responsive solubility might be used as a dissolvable film or a smart capsule.

Poly(N-vinylcaprolactam), a comprehensive review on a thermoresponsive polymer becoming popular

“…One possibility to assemble LbL films of temperature-responsive homopolymers is the use of hydrogen bonding between the layers. [216]. LbL films of the two polymers were prepared at neutral pH at a constant temperature.…”

“…Furthermore, the PNVCL/PHPA multilayer film was relatively stable when it was immersed in buffer solutions near physiological pH at the assembly temperature. The authors suggest that these LbL films with temperaturetriggered solubility can find application as dissolvable layers over smart capsules [216].…”

Dynamically bonded layer‐by‐layer films: Dynamic properties and applications

“…LBL films were also fabricated based on the hydrophobic interaction among the polymer chains. Recently Zhao et al fabricated LBL films from two temperature‐responsive homopolymers, poly( N ‐vinylcaprolactam) (PVCL) and poly(2‐hydroxypropyl acrylate (PHPA). The hydrophobic interaction among the polymer chains is temperature‐dependent; therefore, when the films are immersed in water at a temperature lower than the assembly temperature, they partially or completely dissolve, depending on the immersion temperatures.…”

pH- and temperature-induced release of doxorubicin from multilayers of poly(2-isopropyl-2-oxazoline) and tannic acid

“…LbL films of homopolymers with LCST are mostly constructed via hydrogen bonding interactions among the polymer pairs. Many research groups have previously reported on hydrogen‐bonded multilayers of temperature‐responsive homopolymers including PNIPAM . The studies concerning multilayers of poly(2‐alkyl‐2‐oxazoline)s are limited.…”