Polyethylene oxide blocks

In a similar manner polyisoprene-polyethylene oxide block copolymers can prepared301. It is surprising that the poly(methyl methacrylate) anion can be successfully used for the polymerization of ethylene oxide without chain transfer302. Graft copolymers are also prepared by successive addition of ethylene oxide to the poly-... 

Under these conditions, the polyethylene oxide blocks behave chromatographi-cally invisible and retention of the block copolymer is solely directed by the polypropylene oxide block, yielding fractions of different degrees of polymerization (m) with respect to PPO. The assignment of the peaks was based on comparison with the chromatogram of a polypropylene glycol. 

Fig. 8 (a) Structure-based and (b) source-based Sgroup representation of a polystyrene/ polyethylene oxide block-copolymer... 

Citrate-capped Au NPs have been coated with a layer composed of the double hydrophilic block copolymer polyethylene oxide)-block-poly(2-(dimethylamino)eth-yl methacrylate)-SH (PEO-b-PDMA-SH) leading to core-shell, almost spherical, Au NPs of about 18 nm. The shell cross-linking of these hybrid Au NPs gives rise to high colloidal stability [122]. 

For the case of polyethylene oxide-block-isoprene-block-ethylene oxide) (PEEbtPEO) micelles, the pharmacokinetics and disposition of PEO-PI-PEO in mice was studied after intravenous injection (Rolland et al., 1992). In this study, the cores of the PEO-PI-PEO micelles were cross linked by reaction of isoprene double bonds using UV irradiation along with a photoinitiator. 

Yu et al. (1998) used amphotericin B (AmB), an antifungal drug, as a model to study the release pro-Lle of polyethylene oxide)-block-poly(benzyl-aspartate) (FISSBLA) block copolymer micelles. 

Lavasanifar A., J. Samuel, and G. S. Kwon. 2001. The effect of alkyl core structure on micellar properties of polyethylene oxide)-block-poly(aspartamide) derivative .oll. Surf. B Bioint.22 115-126. 

Yu, B. G., T. Okano, K. Kataoka, S. Sardari, and G S. Kwon. 1998itro dissociation and antifungal ef cacy and toxicity of amphotericin B-loaded polyethylene oxide)-block-pblj nzyli,-aspartate) micelles. 

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. 

Extensive neutron reflectivity studies on surfactant adsorption at the air-water interface show that a surfactant monolayer is formed at the interface. Even for concentration cmc, where complex sub-surface ordering of micelles may exist,the interfacial layer remains a monolayer. This is in marked contrast to the situation for amphiphilic block copolymers, where recent measurements by Richards et al. on polystyrene polyethylene oxide block copolymers (PS-b-PEO) and by Thomas et al. on poly(2-(dimethyl-amino)ethylmethacrylamide-b-methyl methacrylate) (DMAEMA-b-MMA) show the formation of surface micelles at a concentration block copolymer, where an abrupt change in thickness is observed at a finite concentration, and signals the onset of surface micellisation. 

Poloxamer is the generic name for a series of block copolymers that are composed of one polypropylene oxide block sandwiched between polyethylene oxide blocks. For example, poloxamer 188 can be written as (PEO)75-(PPO)3o-(PEO)75. The poloxamers serve as high molecular weight surfactants because the PEG blocks are hydrophilic, whereas the PPO blocks are hydrophobic. 

Alexandridis P, Hatton TA. Polyethylene oxide)-poly(propylene oxide)- polyethylene oxide) block copolymer surfactants in aqueous solutions and at interfaces thermodynamics, structure, dynamics, and modeling (review). Colloid Surf A Physicochem Eng Aspects 1995 96 1-46. 

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]. 

A great deal of research has been performed into the use of poloxamers for the controlled release of active substances [24]. Poloxamers, also referred to as Pluronics or Lutrols, consist of triblock copolymers having a central hydrophobic polypropylene oxide block and on both sides a hydrophilic polyethylene oxide block (Fig. 18.9). 

More precisely defined self-assembly systems than those described in the previous section can be prepared from block copolymers. For example, an amphiphilic polyphosphazene diblock based on roughly equal proportions of [N=P(0CH2CH20CH2CH20CH3)2] , as a hydrophilic block, and [N=PPh(0CH2CH20CH2CH20CH3)] , showed a critical micelle concentration (CMC) of 80 mg/L in an aqueous solution [60], whilst the lower CMC values of 12.4 and 5.2 mg/L are reported for polyethylene oxide-block-poly[bis(trifluoroethoxy)phosphazene]s depending on the block length. Amphiphilic triblock polymers with PPG of the same polyphosphazene showed similar self-assembly behaviour with CMC values in a comparable range [56]. 

Waton, G., Michels, B., Zana, R. Dynamics of micelles of polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymers in aqueous solutions. 

Figure 17 (a) The chemical structure of the amphiphilic liquid crystalline diblock copolymer, p(E0)n4-/)-p(MAAZ)47, which consists of a hydrophilic polyethylene oxide block and a hydrophobic polymethacrylate block with an azobenzene moiety in its side group, (b) 2D GIWAXS and GISAXS patterns obtained at ai= 0.16 ° during heating of the p(EO)-f>-p(MAAZ) thin film with a thickness of 700 nm deposited on a silicon substrate. ... 

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