Hydrophilic-Hydrophobic Polymer Composites

Polystyrene (Dispersed Phase)-Polyacrylamide (Continuous Phase) Composite (Table 6), and 

Initiator (sodium persulfate) Surfactant UxlO gg- 0.3 g 1 of acrylamide 

12 g acrylamide and 28 g water initiator (sodium persulfate) 1.7 x 10 4gg 1 of acrylamide 

The effect of the amount of styrene present in the continuous phase on the stability of the gel is presented in Fig. 30. It should be noted that in the stability experiments the initiators were not introduced into the phases. The gel remained stable until the weight fraction of styrene in the continuous phase reached about 60% and the stability decreased very rapidly beyond this value. This happens because styrene is not sufficiently hydrophobic. 

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If both continuous and dispersed phases of highly concentrated emulsions contain monomeric species, it is possible to obtain hydrophilic/hydrophobic polymer composite materials. Polyacrylamide/polystyrene composites have been prepared in this manner [180], from both w/o and o/w HIPEs containing aqueous acrylamide and a solution of styrene in an organic solvent. 

Ruckenstein, E., and J. S. Park, Hydrophilic-Hydrophobic Polymer Composites, J. Poly. Sci, Part C Pofym.Lett.,26, 529 (1988). 

In the methodology developed by us [24], the incompatibility of the two polymers was exploited in a positive way. The composites were obtained using a two-step method. In the first step, hydrophilic (hydrophobic) polymer latex particles were prepared using the concentrated emulsion method. The monomer-precursor of the continuous phase of the composite or water, when that monomer was hydrophilic, was selected as the continuous phase of the emulsion. In the second step, the emulsion whose dispersed phase was polymerized was dispersed in the continuous-phase monomer of the composite or its solution in water when the monomer was hydrophilic, after a suitable initiator was introduced in the continuous phase. The submicrometer size hydrophilic (hydrophobic) latexes were thus dispersed in the hydrophobic (hydrophilic) continuous phase without the addition of a dispersant. The experimental observations indicated that the above colloidal dispersions remained stable. The stability is due to both the dispersant introduced in the first step and the presence of the films of the continuous phase of the concentrated emulsion around the latex particles. These films consist of either the monomer-precursor of the continuous phase of the composite or water when the monomer-precursor is hydrophilic. This ensured the compatibility of the particles with the continuous phase. The preparation of poly(styrenesulfonic acid) salt latexes dispersed in cross-linked polystyrene matrices as well as of polystyrene latexes dispersed in crosslinked polyacrylamide matrices is described below. The two-step method is compared to the single-step ones based on concentrated emulsions or microemulsions. 

Evani, S., Enhanced Oil Recovery Process Using a Hydrophobic Associative Composition Containing a Hydrophilic/Hydrophobic Polymer, U.S. Pat. 4,814,096 (1989). 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

Starch-plastic composites contain a mixture of two very different types of materials (/) hydrophobic, petrochemical-derived polymers (PE, EAA) known to be highly resistant to degradation by living organisms, and (i7) a hydrophilic, natural polymer (starch) that is easily broken down by a wide array of organisms. In the process developed by Otey (3), these fundamentally incompatible materials are forced into an intimate mixture during production of the plastic film. Since... 

The phase transition is directly related to the hydrophilic/hydrophobic balance in a copolymer and controlling the polymer composition provides a highly effective way of tuning the LCST. Another example of responsive polymer libraries was based on the combination of 2-hydroxypropyl acrylate and DMA or A-acryloyl morpholine [50]. The nitroxide mediated copolymerization conditions were chosen on the basis of the kinetic investigation of the homopolymerizations, as discussed in this chapter (see, e.g., Sect. 2.1.2). 

These discoveries provided the technology base for commercialization efforts of starch-based plastics by the Novon division of the Warner-Lambert Company.157,158 The thermoplastic compositions were based on blends of destructurized starch and various hydrophilic polymers, such as ethylene-vinyl alcohol copolymers (EVOH). Hydrophobic polymers and additives, such as plasticizers and lubricants, could also... 

If the oil phase is replaced in an oil in water (o/w) emulsion by a hydrophobic monomer, or the water phase in a water in oil (w/o) emulsion by a hydrophilic monomer, an emulsion is obtained that can be employed as a precursor for the preparation of polymer latexes [10, 11]. Similarly, if both phases are replaced, the oil phase by a hydrophobic phase containing a monomer and the water phase by a hydrophilic phase containing a monomer, the generated emulsion could be employed as a precursor in the preparation of polymer composites [12]. However, concentrated emulsions that are generated and stable at room temperature may become unstable at the polymerization temperature. To be suitable for the preparation of polymers and polymer composites, the concentrated emulsion must first form and, subsequently, it must remain stable at the temperature at which polymerization takes place. The scope of the present section is to investigate the factors that influence the formation and stability of concentrated emulsions at the preparation and polymerization temperatures in order to identify the physico-chemical conditions that ensure their stability [9],... 

Single-step preparations of composite polymers have been examined in previous sections. The volume fraction of the continuous phase was, however, relatively small in those cases. In contrast, the present method allows us to prepare composites with larger volume fractions of the continuous phase. Composites with large volume fractions of the continuous phase can also be obtained in a single-step by polymerizing an emulsion or a microemulsion [24]. An emulsion of a hydrophobic (hydrophilic) monomer in another hydrophilic (hydrophobic) monomer can be extremely stable (even thermodynamically stable, and then it is called a microemulsion) if a sufficiently large amount of surfactant is introduced into the system. For an emulsion to be thermodynamically stable, a cosurfactant is in most cases needed besides the surfactant. The latter method was used to prepare composites by employing acrylamide... 

It is possible to develop novel polymer-polymer composites or blends by simultaneous or sequential polymerization of hydrophilic and hydrophobic monomers. Preliminary work on microemulsions contidning styrene/acrylamide... 

Comparisons of commonly used XAD resins have been published for the isolation of both fulvic acid (Aiken et al., 1979) and humic acid (Cheng, 1977) from water. These resins differ in pore size, surface area, polymer composition, and polarity (Table 5) (Kunin, 1977). As with anion-exchange resins, hydrophobic styrene-divinylbenzene resins (XAD-1, XAD-2, XAD-4) were found more difficult to elute than hydrophilic acrylic-ester resins (Table 6). This is due to hydrophobic interactions, and possible tt-tt interactions with the aromatic resin matrix of styrene-divinylbenzene resins. In addition, ki-... 

Recently, alternative methods have also been developed to stabilize these complex enzyme systems. The technique of microencapsulation [128] is designed to prevent physically the protease enzyme from interacting with the other enzymes (Figure 8.23). This is accomplished by a composite emulsion polymer system which has a hydrophilic portion attached to a hydrophobic core polymer. The protease is stabilized by trapping it within the network formed by the hydrophobic polymer. 

Supramolecular approaches [5,7,20-22] are also effective for ion conduction in polymers. Ikkala and ten Brinke prepared the complex of polystyrene-frZock-poly(4-vinylpyridine) (PS-fr-PVP) and oligo(ethylene oxide)sulfonic acid 11 [71,72]. The polymer self-assembles into lamellar nanostructures consisting of glassy hydrophobic polystyrene and hydrophilic PEO layers, as shown in Fig. 11. When LiCl04 is dissolved in the polymer composites, lithium ions are complexed and transported in the hydrophilic PEO layers, resulting in high ionic conductivities on the order of 10-6 S cm-1 at ambient temperature. 

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