Hydrophilic polymer

The successful development of eye contact lenses led in turn to a demand for soft contact lenses. Such a demand was eventually met by the preparation of copolymers using a combination of an acrylic ester monomer such as methyl methacrylate, a cross-linkable monomer such as a dimethacrylate, and a monomer whose homopolymer is soluble or highly swollen in water such as N-vinyl pyrrolidone. Such copolymers swell in water (hence the term hydrophilic), the degree of swelling being controlled by the specific type and amount of the monomers used. In use the lens is swollen to equilibrium in water, a typical soft lens having a water content of about 75%. 

Such lenses may be made by machining from rod. More recently processes have been developed where the monomers are cast polymerised in tiny plastics moulds whose cavity corresponds to the dimensions of the lens and using procedures very reminiscent of those described for the manufacture of acrylic sheet (see Section 15.2.2). 

Materials containing the above structure in the polymer chain may be made from copolymers of methacrylic acid and methacrylonitrile. Ammonia-producing additives (such as urea and ammonium hydrogen carbonate) are added to the 

Complete imidation will not occur but that which does will be accompanied by the formation of a cellular structure to produce a rigid cellular polymer. 

The foams, marketed by Rohm as Rohacell, are stable at room temperature to hydrocarbons, ketones, chlorinated solvents and 10% sulphuric acid. They may be used under load at temperature up to 160°C. Uses quoted for these materials include bus engine covers, aircraft landing gear doors, radar domes, domes, ski cores and tennis racket cores. Their potential is in applications demanding a level of heat deformation resistance, solvent resistance and stiffness not exhibited by more well-known cellular polymers such as expanded polystyrene and the polyurethane foams. 

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J. E. Glass, ed.. Hydrophilic Polymers Performance with Environmental Acceptance, Advances in Chemistry Series 248, American Society, Washington, D.C., 1995. 

Hydrogels. Controlled swelling of hydrophilic polymers, derived from the glossy/mbbery properties of polymers, is used to control the rate of dmg release from matrices. In the mbbery state, accompHshed by lowering the polymer s glass-transition temperature to an appropriate level, the dispersed dmg diffuses as the polymer swells in the presence of water. 

Hydrogels, ie, gelatin and agar, have been known for a long time. In the late nineteenth century, Herschel proposed the use of jelly materials on the cornea for the correction of vision (108). In 1960, the use of synthetic hydrogels for contact lenses was proposed and several U.S. patents were obtained for the invention of cross-linked hydrophilic polymers, eg, systems based on 2-hydroxethyl methacrylate [868-77-9] (HEMA) (5) (109—112). 

The abihty to moisturize the stratum corneum has also been claimed for the presence of certain hydrophilic polymers, for example, guar hydroxypropyl trimonium chloride [65497-29-2] on the skin. By far the most popular way to moisturize skin is with humectants, some of which are Hsted in Table 12. It is claimed that humectants attract water from the environment and thereby provide moisture to the skin. 

Carbopol is widely used in cosmetic and pharmaceutical practice as a gel-former. Carbopol resins are hydrophilic polymers which swell in water solutions and transform into the gel form at neutralization. At the elaboration of special cosmetic preparations in which carbopol is used, the problem of raw materials compatibility appears. For example, some extracts of aromatic pectin containing materials destroy the gel structure of carbopol. High contents of bivalent metal ions, in particular calcium ions, destructively influence onto the gel-making ability of the system too. 

Other developments in recent years have been the appearance of tough and heat-resistant materials closely related to poly(methyl methacrylate) and to interesting cross-linked polymers. Amongst these are the so-called hydrophilic polymers used in the making of soft contact lenses. 

Anionic and neutral polymers are usually analyzed successfully on Syn-Chropak GPC columns because they have minimal interaction with the appropriate mobile-phase selection however, cationic polymers adsorb to these columns, often irreversibly. Mobile-phase selection for hydrophilic polymers is similar to that for proteins but the solubilities are of primary importance. Organic solvents can be added to the mobile phase to increase solubility. In polymer analysis, ionic strength and pH can change the shape of the solute from mostly linear to globular therefore, it is very important to use the same conditions during calibration and analysis of unknowns (8). Many mobile phases have been used, but 0.05-0.2 M sodium sulfate or sodium nitrate is common. 

Monomers of the acrylic series exhibit high reactivity in free-radical polymerization, many of them being capable of forming sufficiently hydrophilic polymers. For this reason various acrylates form the principal monomeric basis of hydrogels. 

The second group includes SAHs obtained by radical grafting of acrylonitrile (AN) on natural polymers, mostly starch, under the action of cerium initiators [43 -46, 50, 51], The proper crosslinked hydrophilic polymer is formed at the stage of alkali hydrolysis of grafted polyacrylonitrile (PAN), the final characteristics depending on many factors, in particular the sort of starch [46], the methods of its preparation [51], the component ratio, etc. The nature of starch is exhibited through... 

This molecule is a copolymer with polymethyl methacrylate (PMMA) in acrylic latex paints, where the hydrophobic PMMA is surrounded by hydrophilic polyvinyl acetate molecules. Such a suspension of a hydrophobic polymer wrapped in a hydrophilic polymer is called a latex. 

Associations can be of physical nature too. Chitosan blends with hydrophilic polymers including polyvinylalcohol, polyethyleneoxide and poly-vinylpyrrohdone, were investigated as candidates for oral gingival delivery systems. Chitosan blends were superior to chitosan alone in terms of comfort, ease of processing, film quality, and flexibihty [325]. 

Modification of silicones with hydrophilic polymers has proved to be a more commercially viable solution. 

Hoffman and his coworkers have done a lot of work on the apphcation of radiation-induced graft polymerization for medical apphcation. The hydrophilic polymers that have been used for radiation-induced grafting are Al-vinyl pyrohdone (NVP), 2-hydroxyethyl methacrylate (HEMA), acrylamide (AAm), acrylic acid (AAc), glycidyl methacrylate (GMA), ethyleneglycol dimethacrylate (EGDMA), and ethyl methacrylate (EMA) onto sihcone rubber were widely smdied. 

Hydrophobic or Hydrophilic Polymers with Excellent Mechanical Properties and Flexibility, Tunable Surface Energy for Cardiovascular Applications. Blood Compatibility ... 

Intuitively it might be supposed that a poljrmer with a hydrophilic surface might be more biocompatible than one with a ("foreign ) hydrophobic surface. This simple interpretation is not always correct. Nevertheless, the study of hydrophilic polymers, especially those that promote endothelial tissue overgrowth or ingrowth, is an area of great interest. 

Electric-field-driven transport in media made of hydrophilic polymers with nanometer-size pores is of much current interest for applications in separation processes. Recent advances in the synthesis of novel media, in experimental methods to study electrophoresis, and in theoretical methodology to study electrophoretic transport lead to the possibility for improvement of our understanding of the fundamentals of macromolecular transport in gels and gel-like media and to the development of new materials and applications for electric-field-driven macromolecular transport. Specific conclusions concerning electrodiffusive transport in polymer hydrogels include the following. 

Prange, MM Hooper, HH Prausnitz, JM, Thermodynamics of Aqueous Systems Containing Hydrophilic Polymers or Gels, AIChE Journal 35, 803, 1989. 

W. M. Harms and L. R. Norman. Concentrated hydrophilic polymer suspensions. Patent US 4772646,1988. 

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