Polyethylene oxide diblock copolymer

XPS spectra of polystyrene (top), polyethylene oxide (middle) and a polystyrene-polyethylene oxide diblock copolymer (bottom). 

Sun L, Liu YX, Zhu L, Hsiao BS, AvUa-Orta CA (2004) Self-assembly and crystallization behavior of a double-crystalline polyethylene-block-poly(ethylene oxide) diblock copolymer. Polymer 45 8181-8193... 

Weiyu C, Tashiro K, Hanesaka M, Takeda S, Masunaga H, Sasaki S, Takata M. Relationship between morphological change and crystaUine phase transitions of polyethylene-poly (ethylene oxide) diblock copolymers, revealed by the temperature dependent synchrotron WAXD/SAXS and infrared/Raman spectral measurements. J Phys Chem B 2009 113 2338-2346. 

Polyethylene-fi-poly(ethylene oxide) diblock copolymers (PE-6-PEO) represent an interesting double-crystalline diblock copolymer system since both blocks are strongly segregated and at the same time they have a marked tendency to crystallize in view of their highly flexible linear chains [20]. Hillmyer et al. [271] synthesized PE-6-PEO block copolymers of 2.1 and 2.8 kg/mol from hydroxyl terminated poly(l,4-butadiene) catalytically... 

Poly (ethylene oxide)/poly (butylene oxide) copolymers In polyethylene oxide)-poly(butylene oxide) (PEO-PBO) diblocks with short blocks, unfolded PEO blocks crystallize into lamellar crystals, and the PBO... 

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. 

Amphiphilic block copolymers consisting of a hydrophobic (poly(ethyl ethylene) (PEE) and a hydrophilic polyethylene oxide)(PEO) block form monolayers at the air-water interface. The schematic molecular arrangement of this diblock is shown in Fig. 3.26. 

Desai, H., et al. (2006), Micellar characteristics of diblock polyacrylate-polyethylene oxide copolymers in aqueous media, Eur. Polym. J., 42(3), 593-601. 

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. 

Self-assembled block copolymers are basically amphilic molecules which contain distinctively different polymers. This block copolymer contains two or more polymers quantitatively in the form of blocks. Some of the block copolymers are polyacrylic acid, polymethylacrylate, polystyrene polyethylene oxide, polybutadiene, polybutylene oxide, poly-2-methyloxazoline, polydimethyl sUoxane, poly-e-caprolactone, polypropylene sulfide, poly-A -isopropylacrylamide, poly-2-vinylpyridine, poly-2-diethylamino ethyl methacrylate, poly-2-(diisopropylamino) ethyl methacrylate, poly-2-(methacryloyloxy) ethyl phosphorylcholine, and polylactic acid. These copolymers contain more than polymers to form certain configurations like linear, branched, patterned. For example, if we take three polymers named A, B, and C, they can be combined to form arrangements AB, BA, AA, BAB, ABCAB, ABCABC, ABABAB, etc. in the form of branched configuration it forms (ABQa, (ABA)a, (AB)4, etc. Depending on the above-mentioned number of blocks, they are named as AB diblock copolymers, ABC triblock copolymers, ABC star block copolymers, etc. The covalent linkage between these different blocks of polymers makes macroscopic phase separation impossible, that is, in its place the phase separation... 

Figure 8.3. Surface pressure isotherms for polymethyl methacrylate (PMMA), polyethylene oxide (PEO) and a linear diblock copolymer (mole fiaction of ethylene oxide about 0.5) and the calculated surface pressure (dashed line) using equation (8.1.5). After Rochford (1995).

Figure 8.18. Number density distributions of the surface layer components for a linear diblock copolymer of polymethyl methacrylate and polyethylene oxide spread at the air/water interface (a) a low surface concentration and (b) a higher surface concentration. Solid line, PEO short dashes, water and long dashes, PMMA. After Richards et al. (1994).

Block copolymers are more complex. Only a few remarks arc made below, and immediately after we revat to the more common surfactants, a plan that is followed in the rest of the book. A hnear hydrophihe polymer such as polyethylene oxide (PEO) is attached at one of its terminals to a more hydrophobic polymer such as polypropylene oxide (PPO). The result is an amphiphile PEO-PPO, called a diblock copolyma-. Similarly, PEO-PPO-PEO is a triblock copolymer, another common block copolymer. The blocks range up to hundreds of repeat units. The insoluble block can crystallize or form glass. Ionic blocks are also available, although the nonionic block copolymers are more common. 

Several other di- and triblock copolymers have been synthesized, although these are of limited commercial availability. Typical examples are diblocks of polystyrene-block-polyvinyl alcohol, triblocks of poly(methyl methacrylate)-block poly(ethylene oxide)-block poly(methyl methacrylate), diblocks of polystyrene block-polyethylene oxide, and triblocks of polyethylene oxide-block polystyrene-polyethylene oxide [4]. 

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