Self-Assembled Lamellar Films of Comb-Shaped Copolymers by Segregation between Hydrophobic Side Chains and the Main Chain with Hydrophilic Comonomers

Order-Order Transition in Statistical Copolymer Thin Film Induced by LCST-Type Behavior

In this paper, we describe the formation of an ordered structure in a copolymer thin film through hydration, which subsequently transitions to a different ordered structure upon dehydration. A statistical copolymer of poly(N-octadecyl acrylamide-stat-hydroxymethyl acrylamide) with a comonomer content ratio of 1:1, denoted as p(ODA50/HEAm50), was synthesized via free radical copolymerization. We prepared a thin film of this copolymer on a solid substrate and annealed it at 60 °C under humid conditions. This treatment formed a side-chain segregated lamellar (SCSegL) structure, in which the ODA and HEAm units are oriented perpendicularly to the polymer backbone and opposite each other. Increasing the annealing temperature to 90 °C led to a transition to a side-chain mixed lamellar (SCMixL) structure, where the ODA and HEAm units are also oriented perpendicularly to the polymer backbone but in both directions. The quartz crystal microbalance (QCM) data indicate that p(ODA50/HEAm50) exhibits LCST-like behavior with a transition temperature of approximately 50 °C. We conclude that the formation of the SCSegL structure at 60 °C is due to pronounced segregation between the water-adsorbed HEAm groups and the hydrophobic ODA. Conversely, dehydration at 90 °C reduces the segregation forces, forming the SCMixL structure, which exhibits lower strain. These results demonstrate that the p(ODA50/HEAm50) film undergoes an order-to-order transition driven by the hydration-dehydration process. Additionally, we found that changes in the lamellar structure significantly alter the swelling properties of the film.

Synthesis of the pH-sensitive nanoparticles based on the acylhydrazone bonds conjugated doxorubicin and studies on their in vivo anti-tumor effects

The purpose of this study was to synthesize DHPD polymers through the conjugation of doxorubicin (DOX) molecules onto poly(ethylene glycol) (PEG) chains via acylhydrazone bonds, and to fabricate pH-responsive DHPD nanoparticles (NPs) for investigation of their biosecurity and in vivo anti-tumor activity. The morphology, size distribution, stability, pH-responsiveness, biosecurity, and in vivo anti-tumor effects of the DHPD NPs were evaluated. Characterization of the DHPD polymers using 1H NMR, FTIR, and Raman spectra confirmed their successful synthesis. The DHPD NPs exhibited a round morphology with an average diameter of 144.4 ± 1.7 nm and a polydispersity index (PDI) of 0.23 ± 0.02. Biosecurity studies indicated that the DHPD NPs were non-toxic to treated mice, and in vitro cell tests demonstrated their ability to be taken up by 4T1 cells. Under the acidic microenvironment of 4T1 cells, the acylhydrazone bonds were cleaved, resulting in increased DOX delivery to tumor cells and improved in vivo anti-tumor effects. Animal experiments confirmed that the DHPD NPs reduced DOX toxicity while enhancing its anti-tumor activity. Furthermore, results from the analysis of γ-interferon (INF-γ), tumor necrosis factor-α (TNF-α), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF) indicated that the DHPD NPs improved the anti-4T1 tumor effect of DOX, suggesting their potential application in the treatment of breast cancer.

Order-order transitions in poly(N-octadecyl acrylamide-co-hydroxyethyl acrylamide) statistical copolymer films

This study demonstrates that a simple statistical copolymer can form self-assembled lamellae, whose structures depend on both the comonomer composition and the annealing temperature. Statistical copolymers of octadecyl acrylamide and hydroxyethyl acrylamide [p(ODA/HEAm)] were prepared via free-radical copolymerization, and their thermal properties were studied by differential scanning calorimetry. Thin films of p(ODA/HEAm) were prepared via spin-coating, and their structures were analyzed using X-ray diffraction. It was found that copolymers with HEAm contents between 28 and 50% formed self-assembled lamellae upon annealing at a temperature ∼10 °C above the glass-transition temperature. The self-assembled form was found to possess a "side-chain-mixed" lamellar structure, in which the ODA and HEAm side chains are oriented perpendicular to the lamellar plane composed of the polymer main chain. Interestingly, a copolymer with a HEAm content between 36 and 50% transformed from the side-chain-mixed lamellar structure to generate a "side-chain-segregated" lamellar structure upon annealing at a significantly higher temperature (∼50 °C above T_g). In this structure, the ODA and HEAm side chains were found to be oriented in opposite directions but perpendicular to the lamellar plane. The packing of the side chains in the lamellar structures was studied using Fourier-transform infrared spectroscopy. It was concluded that the structures of the self-assembled lamellae are determined by the strain forces generated during self-assembly, and by the segregation forces existing between the comonomers.