Effects of Hydrophobic Modifications on the Solution Self-Assembly of P(DMAEMA-co-QDMAEMA)-b-POEGMA Random Diblock Copolymers

Interfacial Aggregation Behavior of Double Hydrophilic Block Copolymer of PDMAEMA-b-POEGMA

The detailed micelle/aggregate structures of double hydrophilic diblock copolymers (DHBCs) at the air/water interface are not well understood and need to be further explored. The Langmuir film balance technique and atomic force microscopy were used to study the effects of subphase pH and temperature on the interfacial aggregation behavior of one DHBC of poly[2-(dimethylamino)ethyl methacrylate]-b-poly[oligo(ethylene glycol) methyl ether methacrylate] (PDMAEMA-b-POEGMA) and the structures of its Langmuir-Blodgett (LB) films, respectively. At the air/water interface, the PDMAEMA-b-POEGMA copolymer forms a dense network structure of circular micelles with the hydrophobic carbon backbones of PDMAEMA and POEGMA blocks as the tiny cores and their hydrophilic side chains as the short shells, and each copolymer molecule forms two connected micelles/cores. This ultrafine core-shell micelle structure is successfully identified by using our newly proposed relative aggregation number method, which is different from the isolated core-shell-petal and core-shell-corona structures presented in our previous DHBC systems. With the increase of subphase pH, the isotherms of the copolymer first move toward smaller mean molecular areas (mmA) and then move toward larger ones. Under alkaline conditions, the monolayer exhibits the largest hysteresis degree, whereas that under neutral conditions exhibits the smallest one. As the temperature rises, the isotherms under acidic conditions move to larger mmA due to the increased thermal mobility of the OEGMA side chains. Under neutral and alkaline conditions, the isotherms at 20 °C appear at the left of those at 10 °C due to the collapse of the OEGMA side chains above 15 °C.

Self-Aggregation in Aqueous Media of Amphiphilic Diblock and Random Block Copolymers Composed of Monomers with Long Side Chains

Amphiphilic diblock copolymers and hydrophobically modified random block copolymers can self-assemble into different structures in a selective solvent. The formed structures depend on the copolymer properties, such as the ratio between the hydrophilic and the hydrophobic segments and their nature. In this work, we characterize by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) the amphiphilic copolymers poly(2-dimethylamino ethyl methacrylate)-b-poly(lauryl methacrylate) (PDMAEMA-b-PLMA) and their quaternized derivatives QPDMAEMA-b-PLMA at different ratios between the hydrophilic and the hydrophobic segments. We present the various structures formed by these copolymers, including spherical and cylindrical micelles, as well as unilamellar and multilamellar vesicles. We also examined by these methods the random diblock copolymers poly(2-(dimethylamino) ethyl methacrylate)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (P(DMAEMA-co-Q_6/12DMAEMA)-b-POEGMA), which are partially hydrophobically modified by iodohexane (Q₆) or iodododecane (Q₁₂). The polymers with a small POEGMA block did not form any specific nanostructure, while a polymer with a larger POEGMA block formed spherical and cylindrical micelles. This nanostructural characterization could lead to the efficient design and use of these polymers as carriers of hydrophobic or hydrophilic compounds for biomedical applications.

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Multiple strategies to control the hydrophilic-hydrophobic balance of P(DMA-co-DMAEMA-co-QDMAEMA) coatings

The regulation of the hydrophilic-hydrophobic balance of polymers has an important influence not only on their aggregation behavior in aqueous solution, but also on their adhesion properties on the surface of substrates and the applications of the modified surfaces. Based on this, a random copolymer poly(dopamine methacrylamide-co-2-(dimethylamino)ethyl methacrylate) (P(DMA-co-DMAEMA)) was synthesized as a starting polymer to generate P(DMA-co-DMAEMA-co-QDMAEMA) (PDDQ) derivatives by a programmable quaternization of the DMAEMA precursor. By adjusting the pH or temperature, both the aggregation behavior in aqueous solutions and the surface adhesive behavior on the substrate surfaces of PDDQ copolymers were regulated due to the hydrophilic-hydrophobic balance. Specifically, the surface adsorption of PDDQ copolymers on surfaces was enhanced by the increased hydrophobicity of PDDQ. Stainless steel meshes (SSM) modified with the PDDQ0 copolymer without quaternization showed a superoleophobicity in acidic aqueous media, which endowed it with improved oil-water separation performance. In addition, the hydrophilic-hydrophobic balance of PDDQs and their coatings could also be tuned by changing the ratio of DMAEMA to QDMAEMA in the copolymer. From PDDQ0 to PDDQ100, by increasing the hydrophilic QDMAEMA component of PDDQ copolymers, anti-protein properties and oil/water separation efficiency of the modified surfaces were also enhanced gradually. The results provided a reference for designing P(DMA-co-DMAEMA-co-QDMAEMA) coatings in different application environments.