Polyethylene oxide block copolymers

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-... 

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

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. 

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. 

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

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. 

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]. 

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. 

Polyethylene oxide)—poly(l-lactide)—Poly(ethylene oxide) block copolymer biodegradable/bioerodible... 

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. 

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. 

In most cases the catalytically active metal complex moiety is attached to a polymer carrying tertiary phosphine units. Such phosphinated polymers can be prepared from well-known water soluble polymers such as poly(ethyleneimine), poly(acrylic acid) [90,91] or polyethers [92] (see also Chapter 2). The solubility of these catalysts is often pH-dependent [90,91,93] so they can be separated from the reaction mixture by proper manipulation of the pH. Some polymers, such as the polyethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers, have inverse temperature dependent solubility in water and retain this property after functionalization with PPh2 and subsequent complexation with rhodium(I). The effect of temperature was demonstrated in the hydrogenation of aqueous allyl alcohol, which proceeded rapidly at 0 °C but stopped completely at 40 °C at which temperature the catalyst precipitated hydrogenation resumed by cooling the solution to 0 °C [92], Such smart catalysts may have special value in regulating the rate of strongly exothermic catalytic reactions. 

Semsarzadeh MA, Ghalei B. 2012. Characterization and gas permeabihty of polyurethane and polyvinyl acetate blend membranes with polyethylene oxide-polypropylene oxide block copolymer. J. Membr. Sci. 401-402 97-108. 

Another method of reducing coalescence is the use of macromolecular surfactants such as gums, proteins and synthetic polymers, e.g. A-B, A-B-A block and BA graft copolymers. Examples of such molecules are poly(vinyl alcohol) and polyethylene oxide-polypropylene oxide block copolymers. 

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]. 

Electrical conductivity measurements have been reported on a wide range of polymers including carbon nanofibre reinforced HOPE [52], carbon black filled LDPE-ethylene methyl acrylate composites [28], carbon black filled HDPE [53], carbon black reinforced PP [27], talc filled PP [54], copper particle modified epoxy resins [55], epoxy and epoxy-haematite nanorod composites [56], polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) blends [57], polyacrylonitrile based carbon fibre/PC composites [58], PC/MnCli composite films [59], titanocene polyester derivatives of terephthalic acid [60], lithium trifluoromethane sulfonamide doped PS-block-polyethylene oxide (PEO) copolymers [61], boron containing PVA derived ceramic organic semiconductors [62], sodium lanthanum tetrafluoride complexed with PEO [63], PC, acrylonitrile butadiene [64], blends of polyethylene dioxythiophene/ polystyrene sulfonate, PVC and PEO [65], EVA copolymer/carbon fibre conductive composites [66], carbon nanofibre modified thermotropic liquid crystalline polymers [67], PPY [68], PPY/PP/montmorillonite composites [69], carbon fibre reinforced PDMS-PPY composites [29], PANI [70], epoxy resin/PANI dodecylbenzene sulfonic acid blends [71], PANI/PA 6,6 composites [72], carbon fibre EVA composites [66], HDPE carbon fibre nanocomposites [52] and PPS [73]. 

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). 

The partial molar quantities of mixing were determined for normal and branched alkanes (O5 — Cio), cyclohexane, benzene and tetrachloromethane in polyisobutylene [57]. Partial molar enthalpies of mixing were measured for normal alkenes in low and high density polyethylene, polypropylene, polybutene-1, polystyrene, poly(methyl acrylate), poly(vinyl chloride), polyCN-isopropyl-acrylamide), ethylene-vinyl acetate copolymer, ethylene-carbon oxide copolymer [88] normal, branched and cyclic alkanes, benzene, n-butylbenzene, ois- and ra s-decalin, tetraline and naphthalene in polystyrene at 183, 193 and 203°C [60] these solutes in poly (methyl acrylate) [57] n-nonane, n-dodecane and benzene in polystyrene in the range 104.8 — 165.1 C [71] O7—C, C12 normal alkanes and aromatic hydrocarbons in polystyrene at an average temperature of 204.9°C [72], C7—Cg normal alkanes in poly(ethylene oxide) at an average temperature of 66.5 "C [72] normal alkanes in ethylene oxide—propylene oxide block copolymers (Pluronics L 72, L 64 and F 68) at the same average temperature [72]. 

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]. 

Polyethylene oxide polypropylene oxide block copolymers are large macromolecules with two hydrophilic or two lipophilic blocks, depending on the way they are made. In any case, their size is perfectly comparable with a droplet in a O/W or W/O microemulsion far from the i = 1 interfacial situation or far from a unit water-to-oil ratio case. Such macrosurfactants have been found to be able to link nearby droplets and increase the percolation occurrence of W/O or O/W microemulsions considerably, even at very low internal phase contents [78-80]. 

The second class includes polyethylene glycol alkyl esters, ethoxylated linear aliphatic alcohols, ethoxylated natural fatty acids and oils, and alkanolamides. These products, together with ethylene oxide block copolymers with propylene oxide, form a class of ethoxylate surfactants that are biodegradable. Linear alcohol ethoxylates find extensive use in heavy-duty laundry detergents. 

The newest group of associative thickeners are schematically similar to the HEURs. The polyether segments may include ethylene oxide-propylene oxide block copolymer in place of polyethylene oxide, and the linkages are other than methane (e.g. amide, ether). 

---