Swellability

Organically modified clays can sweU when exposed to organic solvents [97-100], depending on the interaction between the clay surface and solvent, in different scales. The level of dispersion can be correlated to the solubility parameters of solvent and organic modification of the organoclay [100, 101]. 

Besides their role of enhancing solvent-clay surface compatibility already discussed above, some organic modifier molecules may provide functional groups that participate in catalyst supporting reactions [62, 103] or even become copolymerized with the polymer during in-situ polymerization [70]. 

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Hydrophobically Modified Alkali-Swellable Emulsions. The hydrophobe modification of acryHc acid represents an important class of... 

Because 100% DVB is not available commercially, one has to choose either 56% DVB or 80% DVB for the preparation of GPC/SEC gels. The potential components of commercial divinylbenzene are shown in Fig. 5.5. The composition of commercial 56% DVB consists of 56% DVB isomers and 44% ethylstyr-ene and diethylbenzene isomers. The diethylbenzene is nonreactive, but the ethylstyrene acts as styrene in the formulation and tends to produce softer, more swellable GPC gels. Therefore, it is not necessary to actually add styrene to the formulation to produce a ST-DVB gel. Because 80% DVB has only 20% ethylstyrene and diethylbenzene isomers the GPC/SEC gel produced using it would be more rigid and less swellable. 

The grafting reaction depends upon the degree of substitution as well as the kind of pulp used. Introducing acetyl groups in the cellulose chains (high substitution) causes a large reduction of its swellability, which reduces the diffusion of the reactants. Thus, acetylation lowers the graftability of the cellulose. 

The development of water-swellable polymers depends on aspects of their synthesis, properties evaluation, optimization and correlation of these properties with synthesis conditions. Obviously, studying the behavior of SAH in contact with liquid and solid phases of the soil as well as with plants requires developing physical models and algorithms suitable for the prediction of SAH efficiency. 

Most other hydrophilic monomers inclined to radical polymerization (methacrylamide, methacrylic acid, N-vinylpyrrolidone, aminoalkyl and hydroxyalkyl methacrylates) do not form hydrogels with high swellability in water. 

Table 5, Average polymer chain concentration (ape), polymer swellability (S), rotational correlation times of TEMPONE (r) and self-diffusion coefficient of methanol (Zf) in the swollen 2,2% Pd catalysts.

The opposite mechanism is used by a hydrocarbon-swellable elastomer [1857],... 

As an example, consider the use of PVPy as a solid poison in the study of poly(noibomene)-supported Pd-NHC complexes in Suzuki reactions of aryl chlorides and phenylboroiuc acid in DMF (23). This polymeric piecatalyst is soluble under some of the reaction conditions employed and thus it presents a different situation from the work using porous, insoluble oxide catalysts (12-13). Like past studies, addition of PVPy resulted in a reduction in reaction yield. However, the reaction solution was observed to become noticeably more viscous, and the cause of the reduced yield - catalyst poisoning vs. transport limitations on reaction kinetics - was not immediately obvious. The authors thus added a non-functionalized poly(styrene), which should only affect the reaction via non-specific physical means (e.g., increase in solution viscosity, etc.), and also observed a decrease in reaction yield. They thus demonstrated a drawback in the use of the potentially swellable PVPy with soluble (23) or swellable (20) catalysts in certain solvents. 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

This subject can be considered in terms of five different types of molecules or materials (a) biologically inert, water-insoluble polymers (b) water-insoluble polymers that bear biologically active surface groups (c) water-swellable polymeric gels, or amphiphilic polymers that function as membranes (d) water-insoluble but bioerodable polymers that erode in aqueous media with concurrent release of a linked or entrapped bioactive molecule and (e) water-soluble polymers that bear bioactive agents as side groups. 

IV. TRANSPORT IN SWELLABLE POLYMERS A. Swelling and Case II Transport... 

NA Peppas, NM Franson. The swelling interface number as a criterion for prediction of diffusional solute release mechanisms in swellable polymers. J Polym Sci Polym Phys Ed 21 983-997, 1983. 

GWR Davidson IH, NA Peppas. Solute and penetrant diffusion in swellable polymers. V. Relaxation-controlled transport in P(HEMA-co-MMA) copolymers. J Controlled Release 3 243-258, 1986. 

PL Ritger, NA Peppas. A simple equation for description of solute release. 1. Fick-ian and non-Fickian release from non-swellable devices in the form of slabs, spheres, cylinders or discs. J Controlled Release 5 23-35, 1987. 

Zweigle, M.L. and Lamphere, J.C. "Crosslinked, Water-Swellable Polymer Microgels," US Patent 4,172,066(1979). 

W.C. Michie et al. 1995 Distributed fiber sensors using swellable polymers... 

The intrinsic viscosity of microgels described in [9] decreased with increasing fractions of the crosslinking monomer to about 8 ml/g which was still above the theoretical value for hard spheres of about 2.36 ml/g according to the Einstein equation and assuming a density of 1.1 g/ml. Obviously, due to the relatively low fraction of the crosslinking monomer, these microgels did not behave like hard spheres and were still swellable to some extent. 

Arsenault, A. C. Kitaev, V. Manners, I. Ozin, G. A. Mihi, A. Miguez, H., Vapor swellable colloidal photonic crystals with pressure tunability, J. Mater. Chem. 2005, 15, 133 138... 

Nafion-H, a perfluorinated sulfonic acid resin, is another strongly acidic solid that has been explored as alkylation catalyst. Rprvik et al. (204) examined unsupported Nafion-H with a nominal surface area of 0.2 m2/g (surface area of a swellable polymer is difficult to define) in isobutane/2-butene alkylation at 353 K and compared it with a CeY zeolite. The zeolite gave a better alkylate and higher conversion than Nafion-H, which produced significant amounts of octenes and heavy-end products. The low surface area of the resin and questions about the accessibility of the sulfonic acid groups probably make the comparison inadequate. 

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