Hydrophobic polymers, applications

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. 

M.M. Reynolds, M.C. Frost, and M.E. Meyerhoff, Nitric oxide-releasing hydrophobic polymers preparation, characterization, and potential biomedical applications. Free Radical Biol. Med. 37, 926-936... 

C. Tribet, R. Audebert, J.-L. Popot (1997) Stabilisation of hydrophobic colloidal dispersions in water with amphiphilic polymers application to integral membrane proteins. Langmuir, 13 5570-5576... 

Another potential application for zeolite/polymer mixed-matrix membranes is the separation of various liquid chemical mixtures via pervaporation. Pervapora-tion is a promising membrane-based technique for the separation of liquid chemical mixtures, especially in azeotropic or close-boihng solutions. Polydime thy 1-siloxane (PDMS), which is a hydrophobic polymer, has been widely used as the continuous polymer matrix for preparing hydrophobic mixed-matrix membranes. To achieve good compatibility and adhesion between the zeolite particles and the PDMS polymer, ZSM-5 was incorporated into the PDMS polymer matrix, the resulting ZS M -5/ P DM S mixed-matrix membranes showed simultaneous enhancement in selectivity and flux for the separation of isopropyl alcohol from water. It was demonstrated that the separation performance of these membranes was affected by the concentration of the isopropyl alcohol in the feed [96]. 

Blends of starch and a hydrophobic polymer make it possible to overcome the disadvantages described above. Starch compounds with Ecoflex are used to enhance hydrophobicity as well as the mechanical and thermal properties of compounded products. To obtain high quality film products, the starch has to be treated before being blended with Ecoflex . The crystalline structure of starch granules has to be destroyed because starch granules are as large as the film thickness of typical film applications and would therefore reduce the mechanical properties of the films. 

EC is an inert, hydrophobic polymer that has been studied substantially for its application as a matrix-forming material in direct compression tablets. Direct compression is the preferred method of manufacture for producing tablets intended for immediate or sustained release. There have been reports on the compressibility and compatibility of EC [307-310] and on its use as a matrix-forming material in direct compression tablets for the delivery of soluble and poorly soluble drugs [311-316]. Tablet hardness [310,314,315], the particle size of the polymer [314,315,317], and the viscosity grade [313,314] were observed to directly affect the drug release rate. It was noted that tablet hardness affected the... 

For the past several years, our laboratory has studied the swelling properties of weakly basic, hydrophobic polymer gds. The gels are formed by bulk polymerization of hydro diobic n-alkyl methacrylates (n-AMA) with N,N-dimethylaminoethyl methacrylate (D( ), tte latter comonomer bearing a tertiary amine sidediain. To form a three-dimensional polymer network that will not dissolve upon swelling, small amounts of the crosslinker divinylbenzene (DVB) are added. These gds, when placed in aqueous solutions, absorb minimal amounts of water in neutral and alkaline media, but become swollen in addic media. Hence, they might be considered for applications in which drug release in the stomach is desirable. 

Among the many classes of polymeric materials now available for use as biomaterials, non-degradable, hydrophobic polymers are the most widely used. Silicone, polyethylene, polyurethanes, PMMA, and EVAc account for the majority of polymeric materials currently used in clinical applications. Consider, for example, the medical applications listed in Table A.l most of these applications require a polymer that does not change substantially during the period of use. This chapter describes some of the most commonly used non-degradable polymers that are used as biomaterials, with an emphasis on their use in drug delivery systems. 

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