PO block

The term poloxamer is widely used to describe a series of ABA block coploymers of polyethylene oxide and polypropylene oxide, extensively used in industry as antifoams, emulsifiers, wetting agents, rinse aids, and in numerous other applications [1-5]. Poloxamers are amphiphilic in character, being comprised of a central polypropylene oxide (PO) block, which is hydrophobic, sandwiched between two hydrophilic polyethylene oxide (EO) blocks as shown below ... 

For the central PO block to serve as an effective hydrophobe, the value of n must be at least 15 the value of m in commercially manufactured poloxamers is such that the EO blocks constitute between 10-80% of the total polymer mass. The absolute and relative masses of the hydrophilic and hydrophobic blocks, on which the physico-chemical properties of the polymers depend, can be controlled during manufacture, enabling the production of poloxamers tailored to specific applications. 

It is important to recognize that the following analytical methods essentially determine EO-PO ratio ( H NMR, IR, cleavage methods) or even simply alkylene oxide content (compleximetric methods) of the analyte, and as such are not specific quantitative or qualitative methods for poloxamers, since EO-PO copolymers of a different structure (for instance, random copolymers, or PO-EO-PO block copolymers) may respond to the methods in a way indistinguishable from poloxamers. The principal technique that permits definitive identification of a sample as a poloxamer is C NMR, which allows structural details, such as the distribution of EO and PO units along the polymer chain, to be elucidated [10]. 

Nonionic surfactants, including EO-PO block copolymers, may be readily separated from anionic surfactants by a simple batch ion exchange method [21] analytical separation of EO-PO copolymers from other nonionic surfactants is possible by thin-layer chromatography (TLC) [22,23] and paper chromatography [24], and EO-PO copolymers may themselves be separated into narrow molecular weight fractions on a preparative scale by gel permeation chromatography (GPC) [25]. 

Surfactants used as lubricants are added to polymer resins to improve the flow characteristics of the plastic during processing they also stabilise the cells of polyurethane foams during the foaming process. Surfactants are either nonionic (e.g. fatty amides and alcohols), cationic, anionic (dominating class e.g. alkylbenzene sulfonates), zwitterionic, hetero-element or polymeric (e.g. EO-PO block copolymers). Fluorinated anionic surfactants or super surfactants enable a variety of surfaces normally regarded as difficult to wet. These include PE and PP any product required to wet the surface of these polymers will benefit from inclusion of fluorosurfactants. Surfactants are frequently multicomponent formulations, based on petro- or oleochemicals. 

The chromatogram in Fig. 17.15 reflects the oligomer distribution of the PO inner block, but does not give any information on the chain lengths of the PEO outer blocks or the total molar mass. This lack of information can be compensated by 2D liquid chromatography. Fig. 17.16 represents the contour plot of the 2D separation of the block copolymer in the sequence LCCC versus SEC. The separation with respect to the PO block length is now obtained along the ordinate, while the abscissa reflects... 

AE and AP surfactants are synthesised by polymerisation of monomeric or short chain oligomeric glycol moieties. If mixtures of ethylene and propylene glycols, however, were applied for the synthesis, so called EO/PO block polymers in the form of complex mixtures with the general formula R-0-(E0)m-(P0) -H and the structure as shown with their... 

It turned out that for all the polymeric amphiphiles of the (EO) -(PO)m-(EO) type there was an increase in enantioselectivity compared with the reaction without amphiphile. Moreover, the ratio of the length of the (PO) block compared with the (EO) block seemed to determine enantioselectivity and activity and not the cmc (critical micelle concentration). A (PO) block length of 56 units works best with different length of the (EO)n block in this type of hydrogenation [30]. for the work-up of the experiments, G. Oehme et al. used the extraction method, but initial experiments failed and the catalyst could not be recycled that way. To solve this problem the authors applied a membrane reactor in combination with the amphiphile (EO)37-(PO)5g-(EO)37 (Tab. 6.1, entry 9) [31]. By doing so, the poly-mer/Rh-catalyst was retained and could be reused several times without loss of activity and enantioselectivity by more than 99%. 

Experimental evidences of the influences of the new PA(P0)2 molecular architecture on the surface activity are gathered hereafter for the copolymers based on both PA and PO blocks. 

Riess demonstrated recently that poly(styrene-b-oxirane) copolymers could act as non-ionic surfactants and lead to water/ toluene microemulsions (29, 30). Using isopropanol as cosurfactant, both 0/W and W/0 microemulsions are obtained (3l). This is a very important conclusion, since PO based diblock copolymers give rise only to 0/W microemulsions under the same experimental conditions (8, 31,). In this respect the "branched structure" of the PO hydrophilic component could favor a decrease in the packing density of the inverse micelle forming molecular and explain the different behavior of the linear and star-shaped PS/PO block copolymers in the W/0 microemulsification process. 

The criterion of stability (R) is the constant limit value of the emulsified volume percentage at 20°C (32, 32.). It appears that 7/3 water toluene emulsions are more efficiently stabilized by star-shaped block copolymers whereas linear block copolymers give better results for 3/7 water toluene emulsions the stability of the l/l water toluene emulsions seems to be insensitive to the molecular architecture of PTBS/PO block copolymers. 

The surfactant properties of polymeric silicone surfactants are markedly different from those of hydrocarbon polymeric surfactants such as the ethylene oxide/propylene oxide (EO/PO) block copolymers. Comparable silicone surfactants often give lower surface tension and silicone surfactants often self-assemble in aqueous solution to form bilayer phases and vesicles rather than micelles and gel phases. The skin feel and lubricity properties of silicone surfactants do not appear to have any parallel amongst hydrocarbon polymeric surfactants. 

These inerts are mostly polymeric or oligomeric in nature and can be both nonionic and anionic. They have multiple binding / interaction sites to the interface, so that a displacement becomes improbable. Several materials have been made available to the industry [6d,ej. The chemistries range from sulfonic condensates (Morwet) or lignin sul-phonates (Reaxx) to EO-PO-block copolymers (Pluronics), comb graft polymers, acrylate based copolymers or various other block copolymers. 

Addition of EO-PO block copolymers to detergents to increase solubility... 

By using two oxiranic monomers, such as PO and EO, it is possible to obtain a great variety of polyether polyols homopolymers of PO, block copolymers PO-EO (with terminal or internal poly[EO] block) or random copolymers (heteropolyethers) of PO-EO, diols or triols of different MW. 

A similar polyether polyol, having the same EO and PO content but in the form of a block copolymer (internal poly[EO] block and terminal poly[PO] block), gives a solid polyether in the form of a wax, probably due to the crystallisation of poly[EO] chains. 

The pseudoliving character of PO anionic polymerisation produces a large variety of block copolymers, by simply changing the nature of the oxirane monomer because the catalytic species (potassium alcoholate) remains active during and after the polymerisation reaction. Thus, if a polyether is synthesised first by anionic polymerisation of PO and the polymerisation continues with another monomer, such as EO, a block copolyether PO-EO with a terminal poly[EO] block is obtained. Another synthetic variant is to obtain a polyethoxylated polyether first by the anionic polymerisation of EO initiated by glycerol [108], followed by the addition of PO to the resulting polyethoxylated triol. A block copolyether PO-EO is obtained with internal poly[EO] block linked to the starter. Another possibility is to add the monomers in three steps first PO is added to glycerol, followed by EO addition and finally by the addition of PO. A copolyether triol block copolymer PO-EO with the internal poly[EO] block situated inside the polyetheric chain between two poly[PO] blocks is obtained [4, 100, 101]. 

Demelan. [Pulcra SA] Sulfate and sulfonate blends and EO/PO block polymers detergent, coupling agent for dishwashers, heavy-duty detergents, hand cleaners, textile scouring. 

Dissolvan Brands. [Hoechst AC] 0/ PO block polymers and/or oxyall lated resins emulsion breaker for w/o emulsions dehydration and desalting agents for crude oil. 

Hoe S. (Hoechst Cdanese/Colwants Surf.] Quateinaries, alcohol ethoxy lates/piqmxylates, EO/PO block co polymers, other surfactants f[Pg.173]

Monoian . [HarcrosUK] EO-PO block polymer emulsifier, stabilizer, detergent, wetdng agent, antifoam for industrial and domestic detergents, emulsion polymerization, latex, detergents, synthetic lubricants, metal cleaning, resin plasticizers, textile processing. 

Poly-Tergent . [Olin] Alkoxylated linear alcohol or EO/PO block polymers surfactant wetting agent defoamer, emulsifier, dedusting dispersant for household and industrial detergents. 

Soprophor . [Rhone-Poulenc Surf. Rhone-Poulenc Geronazzo SpA] Al-koxylated alcohols, EO/PO block polymers, sulfonates, or ethoxylates surfactant wetting and suspen g agents for degreasers, add pidding conqxls., pesticides. 

Tetronk(9. [BASF] EO/PO block copolymers emulsifler, thickener, wetting agent, dispersant, solubilizer, sta-bilizo-, antistat to cosmetics, pharmaceutic, petroleum, detergents, molding powdm, metal treatment, emulsion polymerization, paints, cutting fluids, rubber vulcanization. 

TcxadrO. [Henkel/Emeiy/Cospha] EG/ PO block copdymer low foaming wetting agent, coemulsifier. 

---