Polyurethane hydrophilic

Special rules apply to the world of hydrophilic polyurethanes. These alternate rules are based on the fact that hydrophilic polyurethanes can and should be processed in water. Rather than emulsifying a prepolymer with a polyol, as would be done with a hydrophobic polyurethane, hydrophilics are mixed with water. While the properties of the foam are governed loosely by the guidelines described above, one has more flexibility and control of the formulation and process by which the polyurethane is made. For example, the water can serve as a heat sink to closely control the temperature of the foam the water controls the rate of reaction. 

Cationic, anionic, and amphoteric surfactants derive thek water solubiUty from thek ionic charge, whereas the nonionic hydrophile derives its water solubihty from highly polar terminal hydroxyl groups. Cationic surfactants perform well in polar substrates like styrenics and polyurethane. Examples of cationic surfactants ate quaternary ammonium chlorides, quaternary ammonium methosulfates, and quaternary ammonium nitrates (see QuARTERNARY AMMONIUM compounds). Anionic surfactants work well in PVC and styrenics. Examples of anionic surfactants ate fatty phosphate esters and alkyl sulfonates. 

Two general methods of improving polymer hemocompatibility are known (1) grafting of hydrophilic chains, and (2) the chemical attachment of an antiplatelet agent. In this respect, many hydrophilic and other monomers are grafted on solid polyurethane surfaces such as... 

Essentially nonionic soil-release agents comprise polyesters, polyamides, polyurethanes, polyepoxides and polyacetals. These have been used mainly on polyester and polyester/ cellulosic fabrics, either crosslinked to effect insolubilisation (if necessary) or by surface adsorption at relatively low temperature. Polyester soil-release finishes have been most important, particularly for polyester fibres and their blends with cellulosic fibres. These finishes, however, have much lower relative molecular mass (1000 to 100 000) than polyester fibres and hence contain a greater proportion of hydrophilic hydroxy groups. They have been particularly useful for application in laundering processes. These essentially nonionic polymers may be given anionic character by copolymerising with, for example, the carboxylated polymers mentioned earlier these hybrid types are generally applied with durable press finishes. 

Interfacial behavior of different silicones was extensively studied, as indicated in Section 3.12.4.6. To add a few more examples, solution behavior of water-soluble polysiloxanes carrying different pendant hydrophilic groups, thus differing in hydrophobicity, was reported.584 A study of the aggregation phenomena of POSS in the presence of amphiphilic PDMS at the air/water interface was conducted in an attempt to elucidate nanofiller-aggregation mechanisms.585 An interesting phenomenon of the spontaneous formation of stable microtopographical surface domains, composed primarily of PDMS surrounded by polyurethane matrix, was observed in the synthesis of a cross-linked PDMS-polyurethane films.586... 

From the results presented in this chapter we can conclude that it is feasible to prepare sugar-based polymers analogous to the more qualified technological polymers - polyamides, polyesters, polyurethanes - with an enhanced hydrophilicity and degradability. However, in most cases, the high costs associated with the preparation of the monomers restrict the application of these polymers to biomedical applications and other specialized fields. More readily available monomers and simpler polymerization processes have to be found if sugar-derived polymers should compete with petrochemical-based polymers that are used in domestic applications. 

Polyurethane hydrogels derived from UV curable urethane prepolymer and hydrophilic monomers were prepared and their properties were evaluated. The urethane prepolymer used in this study contained well-defined hard segments centered with a polyether-based soft segment and end-capped with methacrylate groups. The hydrophilic monomers studied were 2-hydroxyethyl methacrylate (HEMA), N-vinyl pyrrolidone, and glycerol methacrylate. Methacryloxypropyl tris(trimethysiloxy) silane (TRIS) was also used in some cases to modify properties. All compositions were UV... 

This paper describes a method for improving hydrophilicity by using radiation-induced grafting of flexible polyurethane (polyether) foam with polar vinyl monomers. By this procedure, the normally hydrophobic material can be converted into a remarkably water-wettable sponge. 

I must thank those who have molded our education in polyurethanes. Since the last book, my focus has moved from hydrophilic polyurethanes to more broad-based applications of this chemistry. While I still do not consider myself an expert in the field of PUR chemistry, I have tried to apply it to a broad range of practical uses and approach the subject from the perspective of a PUR researcher rather than as a manufacturer. 

He is known worldwide for his expertise in the development of a broad range of products based on hydrophilic polyurethane and has authored a book on the subject. He has published a number of papers on the use of polyurethanes in medical and other applications. He has conducted seminars in the U.S. and Europe on the medical applications of specialty polyurethanes. He has been an invited speaker to a number of conferences and seminars. 

Foamex Corporation Product Literature FS-998-F-5, Eddystone, PA 19022, 1998. Thomson, T., Hydrophilic Polyurethanes, CRC Press, 2000, chap. 6. 

Thomson, Hydrophilic Polyurethane for the Delivery of Skin Care Ingredients, US patent Application No. US 2002/0182245 Al, 2002. 

While this book covers the full range of polyurethane chemistries to one degree or another, our perspective has been on the chemical nature of the molecule. Unlike most polyurethane chemists, we have worked almost exclusively on hydrophilic polyurethanes. This specialty grade of polymer (which we will describe at length) is valued for its chemical properties (ability to absorb water, for instance) almost to the exclusion of its physical properties. 

The current libraiy of polyurethanes has some utility, and we will illustrate their uses with examples from our laboratory and from others. Currently, hydrophobic polyurethanes can be used to extract nonpolar pollutants, for example, from some pesticides. At the other end of the spectrum, hydrophilic polyurethanes can be used to extract sparingly soluble organic pollutants from groundwater. We will illustrate this with the extraction of methyl-tert-butylether. 

Consider the procedure for immobilizing an enzyme using polyurethane technology. A solution of the enzyme is produced in water. The solution is then emulsified with a hydrophilic polyurethane prepolymer. The emulsion is applied to the structural members of a reticulated foam by means of nip rollers. After curing... 

Our proposal is not theoretical. Researchers have used reticulated hydrophobic polyurethanes as liver assist devices with some success. We will discuss this research and future work in detail later. For now, it is useful to present an overview. Matsushita et al. inoculated a reticulated polyurethane with porcine hepatic cells, "fhe device functioned as noted, but it was necessary to separate the plasma from the blood because conventional hydrophobic polyurethanes are not hemocompatible. In addition, the technique made no provision for cell attachment. Workers in our laboratory grafted a hydrophilic polyurethane to the structural members of a hydrophobic reticulated foam in an effort to make the composite hemocompatible. Additionally, this gave us the opportunity to add cell attachment proteins. 

As noted, most commercial polyurethanes are useful because of their physical properties. Except in the field of hydrophilic polyurethanes, little work has been done on the chemistry of polyurethanes. We hope this book will change that to a degree. Until then, however, basic research in this area will require the production of your own polymers. 

We will cite more examples of polyurethanes based on polyethers than on polyesters. The polyethers are more easily designed when the polarity of the backbone is important. For instance, one can use polyethers to construct polyurethanes that are hydrophilic or hydrophobic or react to water at all levels between these extremes. Polyethers permit the development of biocompatible and hemocompatible devices. Lastly, they are more hydrolytically stable and so are more appropriate for environmental studies. 

The reaction shown in Figure 2.6 produces what is referred to as a prepolymer via the production method of choice before the one-shot process was developed. Prepolymers are still commonly used. Small molding operations, elastomers, and hydrophilic polyurethanes involve production of prepolymers. 

The nature of a hydrophilic prepolymer permits the addition of large amounts of water. The isocyanate reacts with the water to abstract COt. The amine that also results from the reaction then reacts with an isocyanate group to produce a urea linkage. The reaction continues until the water or the isocyanates are consumed. If provisions are made to trap the CO2 in the mass, a foam is produced. If such provisions are not made, the CO, will bubble away, leaving behind a low gel-strength hydrogel. Careful examination of the resultant molecule might cause one to rename it a polyurethane/polyurea. 

One of the great strengths of polyurethane chemistry is the degree to which one can change its design features with small changes in chemistry. In the field of hydrophilics, the same capital equipment and reaction parameters can be used, but... 

The void volume can be determined by displacement in water. This is problematic when investigating a hydrophilic polymer or when accurate measurements are required. A good estimate of void volume can be obtained by comparing the absolute density of the polymer with the bulk density determined via ASTM D3574-95. For instance, let us assume that isocyanate and the polyol have specific gravities of 1.0. If a polyurethane is made of this combination, the absolute density of the polymer... 

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