Hydrophilic polymers polyethylene oxide

These dressings are sheets of three-dimensional networks of cross-linked hydrophilic polymers (polyethylene oxide, polyacrylamides, polyvinylpyrrolidone, carboxymethylcellulose, modified corn starch). Their formulation may incorporate up to 96% bound water, but they are insoluble in water and they interact by three-dimensional swelling with aqueous solutions. The polymer physically entraps water to form a solid sheet and they have a thermal capacity that provides initial cooling to the wound surface. A secondary dressing is required. 

Calvo, P. Remunan-Lopez, C. Vila-Jato, J.L. Alonso, M.J. Novel hydrophilic chitosan-polyethylene oxide nanoparticles as protein carriers. J. Appl. Polym. Sci. 1997, 63, 125-132. 

A current hypothesis, which is receiving considerable attention, is that one can indeed produce a surface which actively repels proteins and other macromolecules123 124, 133). The basic idea is presented in Fig. 25, which shows that a neutral hydrophilic polymer, which exhibits considerable mobility or dynamics in the aqueous phase, can actively repel macromolecules from the interface by steric exclusion and interface entropy methods. This method has been well-known and applied in the field of colloid stability for many years 120). The most effective polymer appears to be polyethylene oxide, probably because of its very high chain mobility and only modest hydrogen bonding tendencies 121 123>. 

Pharmaceutical research on polymeric micelles has mainly focused on two kinds of block copolymers, namely, AB block copolymers or diblock copolymers and ABA or BAB block copolymers known as triblock copolymers (Bader et al., 1984 Yokoyama et al., 1990,1991 Kwon and Okano, 1996, 1999 Kwon, 1998, 2003 Alakahov and Kabanov, 1998). The most common hydrophilic block (A) of the block copolymers is polyethylene oxide (PEO). This polymer is highly hydrated through hydrogen bonding and sterically stabilizes surfaces of the polymeric micelles in aqueous systems. 

Recently, a new class of inhibitors (nonionic polymer surfactants) was identified as promising agents for drug formulations. These compounds are two- or three-block copolymers arranged in a linear ABA or AB structure. The A block is a hydrophilic polyethylene oxide) chain. The B block can be a hydrophobic lipid (in copolymers BRIJs, MYRJs, Tritons, Tweens, and Chremophor) or a poly(propylene oxide) chain (in copolymers Pluronics [BASF Corp., N.J., USA] and CRL-1606). Pluronic block copolymers with various numbers of hydrophilic EO (,n) and hydrophobic PO (in) units are characterized by distinct hydrophilic-lipophilic balance (HLB). Due to their amphiphilic character these copolymers display surfactant properties including ability to interact with hydrophobic surfaces and biological membranes. In aqueous solutions with concentrations above the CMC, these copolymers self-assemble into micelles. 

As an inorganic mineral, most unmodified nanoadditives are strongly hydrophilic and are generally compatible and miscible only with a few hydrophilic polymers, for instance, clay can only be made into PNs with polyethylene oxide),27 poly(vinyl alcohol),28 and a few other water soluble polymers. Most polymers are hydrophobic and thus they are neither compatible nor miscible with the unmodified nanoadditives, leading to an inability to achieve a PN with a good nanodispersion in most cases. Therefore, for most nanoadditives that have been used to prepare the PNs, an important and necessary feature is their surface treatment that provides compatibility to the nanoadditives and enables them to be uniformly dispersed (and/or separated into single nanoparticles) in the polymer matrix. 

Nanogels Cross-linked hydrophilic copolymers, e.g., Pluronic-poly(ethylenimine) (PEI) and polyethylene oxide (PEO)-PEI Covalent conjugation of polymers 20,51,52... 

For polymer chemists it is interesting to know how well-known linear polymers can be linked with dendritic architectures and what the supramolecular consequences of this approach might be. Combination of dendrimers with linear polymers in hybrid linear-dendritic block copolymers has been employed to achieve particular self-assembly effects. Block copolymers with a linear polyethylene oxide block and dendritic polybenzylether block form large micellar structures in solution that depend on the size (i.e., the generation) of the dendritic block [10]. Amphiphilic block copolymers have been prepared by the combination of a linear, apolar polystyrene chain with a polar, hydrophilic poly(propylene imine) dendrimer [11] as well as PEO with Boc-substituted poly-a, -L-lysine dendrimers, respectively [12]. Such block copolymers form large spherical and cylindrical micelles in solution and have been described as superamphi-philes and hydra-amphiphiles , respectively. 

In analogy to lipids, amphiphilic block copolymers, i.e., macromolecules composed of at least one hydrophilic and one hydrophobic, covalently linked, polymer chains can form in aqueous solutions vesicles the so-called polymersomes. Generally, in self-assembling copolymer solutions, a rich diversity of morphologies is possible. An overview of the various factors important for vesicle formation, including copolymer architecture, presence of additives, solvent composition, and temperature, is given in [19]. To illustrate polymersome structures we reproduce from [21] on the top row of Fig. 2 cryo-TEM images of vesicles formed by 1.0 wt % aqueous solution of PEO- -PBD (PEO, polyethylene oxide PBD, polybutadiene) diblock copolymer for three different sizes of the PEO and PBD blocks. 

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