Pluronic surfactants properties

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. 

Figure 47.2. Pluronic block copolymers with various numbers of hydrophilic EO (n) and hydrophobic PO (m) 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 at concentrations above critical micelle concentration (CMC) these copolymers self-assemble into micelles.

Pluronics, also known as poloxamers, are a class of synthetic block copolymers which consist of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO), arranged in an A-B-A triblock structure, thus giving PEO-PPO-PEO (Fig. 11.7) (Batrakova and Kabanov 2008). They can be found either as liquids, pastes or solids (Ruel-Gariepy and Leroux 2004). Due to their amphiphilic characteristics (presence of hydrophobic and hydrophilic components), pluronics possess surfactant properties which allow them to interact with hydrophobic surfaces and biological membranes (Batrakova and Kabanov 2008). Being amphiphilic also results in the ability of the individual block copolymers, known as unimers, to combine and form micelles in aqueous solutions. When the concentration of the block copolymers is below that of the critical micelle concentration (CMC), the unimers remain as molecular solutions in water. However, as the block copolymer concentration is increased above the CMC, the unimers will self-assemble and form micelles, which can take on spherical, rod-shaped or lamellar geometries. Their shapes depend on the length and concentration of the block copolymers (i.e. EO and PO), and the temperature (Kabanov et al. 2002). Micelles usually have a hydrophobie eore, in this case the PO chains, and a hydrophilic shell, the EO ehains. 

Block copolymers consisting of segments with widely separated solubility characteristics have generated considerable interest because of their unusual surfactant properties. In fact, one of the earliest commercial block copolymers were the Wyandotte "Pluronics." These were poly(propylene oxide-b-ethylene oxide) prepared by sequential addition of ethylene oxide to sodium alkoxide initiated propylene oxide (37,38). Szwarc (39) and others (40,41) prepared poly(styrene-b-ethylene oxide) by addition of ethylene oxide to polystyrene anions in tetrahydrofuran. Other syntheses of AB or ABA block copolymers of styrene-ethylene oxide include sequential addition in various solvents, and coupling reactions (42,43). 

Allen et al. [99-102] took advantage of the gel properties of Pluronic surfactants to create gel compositions for shoe construction. This shoe had a liquid-... 

Lowe, K. C., B. A. Furmidge, S. Thomas, Hemolytic properties of Pluronic surfactants and effects of purification, Artif. Cells, Blood Substitutes, Immobilization BiotechnoL, 1995, 23, 135-139. 

There is a vast body of diblock copolymer studies since block choice can be such that they resemble amphiphilic surfactants. For the sake of brevity, we will skip them. Instead, we present an interesting case of triblock copolymers of poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, commonly known by one of its trade names, Pluronics [117]. They have been used as non-ionic surfactants for a variety of applications such as in emulsification and dispersion stabilization. In aqueous solutions, these copolymers form micelles, and there exists a well-defined critical micelle concentration that is experimentally accessible. Several groups have investigated colloidal suspensions of these polymers [118-122], The surface properties of the adsorbed monolayers of the copolymers have been reported with respect to their structures and static properties [123-126]. 

The poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block copolymers were also used to gel the continuous aqueous phase. Poloxamers may be used as the secondary hydrophilic surfactant in the preparation of the w/o/w system, and the finished emulsion is then irradiated. The polymerisation reaction can be monitored by cone-and-plate viscometry. Fig. 9 shows the flow curve obtained for a water/isopropyl myristate/water emulsion as a function of the radiation dose. As the dose of y-irradiation is increased, the viscosity of the w/o/w emulsion increased up to a gel-point1. The gel-point of the emulsion is dependent on the type and concentration of poloxamer. In the example shown, prepared using a mixture of 5% (w/v) Pluronic F87 and 5% (w/v) Pluronic F88 in the external phase, the gel-point was reached at 4.2 (Fig. 9). Fig. 10 shows the changes in the properties of irradiated systems on storage. 

In agreement with the data presented in Tables VIII. 1 and VIII.2, large variation in HLB numbers may be achieved with pluronics (see Chapter 11,3), which are the block co-polymers of ethylene oxide (group number of 0.33) and propylene oxide (group number of -0.15). Here it is worth pointing out that the HLB number primarily reflects the difference between hydrophobic nature of hydrocarbon chain and hydrophilic nature of polar head of surfactant molecules. For surfactants to reveal stabilizing properties, both of these factors have to be strongly expressed. 

Table 11.74 Properties of PLURONIC and TETRONIC Block Copolymer Surfactants (47)...

KIT-5 is a porous silica material with properties similar to those of SBA-16 the mesopores are ordered in a cubic face-centered Fm-3m symmetry. Similarly to SBA-16, KIT-5 is synthesized in a ternary water, n-butyl alcohol, and Pluronic F127 surfactant system with emphasis on a low HCl concentration in aqueous solution [147]. FDU-12 also represents a cubic (Fm-3m) mesostructure with a large... 

Poly(ethylene oxide)/Poly(propylene oxide)/ Poly(ethylene oxide) Triblock Copolymer Pluronic is a trade name for poloxamers, which are nonionic triblock copolymers of PEO chains on the two ends of the molecules with a poly(propylene) oxide (PPO) chain in the middle. The PEO chain is hydrophilic, while the PPO chain is hydrophobic. The polymer properties can be tailored depending on the content ratio of the constituents. Due to the combined hydro-phobic and hydrophilic properties in the structure (amphiphilic), it can be used as a stabilizer and a surfactant. It also can enhance miscibility and water absorption of polymers, and it has low toxicity itself. Pluronic has been used in drug delivery devices for controlled release purposes [220]. 

---