Monomer hydrophilic

The Smith-Ewart expression (eq. 1) accurately predicts the particle number for hydrophobic monomers like styrene and butadiene (21), but fails to predict the particle number (22) for more hydrophilic monomers like methyl methacrylate and vinyl acetate. A new theory based on homogeneous particle... 

Hydrogels used for contact lens appHcations can be classified based on the chemical stmcture of hydrophilic monomers and on the water content of the hydrogel lens. These classifications are not unique because the design of hydrogels is based on the performance desired in most cases, more than one component is used for the same or complementary purpose. In fact, some hydrophilic monomers are used in both high water and low water lenses. 

The water content of a hydrogel depends on the hydrophilicity of the monomer, eg, cured poly(HEMA) absorbs 60% of its weight of water and thus forms a hydrogel with about 38% water content. Other hydrophilic monomers, such as A/-vinylpyrrohdinone [88-12-0] (NVP) (6), and glycerol methacrylate [100-92-5] (GM) (7), and acrylamide monomers, such as diacetone acrylamide [2873-94-9] (DAA), have also been used to form hydrogels with higher water content. 

Because of the many choices of hydrophilic monomers, cross-linkers, and hydrophobic monomers, a large number of formulations have been developed and manufactured into hydrogel lenses. The water content of these hydrogel lenses ranges from about 38%, for HEMA-based lenses, to 80%, for poly(vinyl alcohol) and partially hydrolysed acrylonitrile lenses. Table 2 gives a representative Hst of FDA approved hydrogel materials available to the consumer in the early 1990s. 

The principal problems for sdicone mbber as a viable lens material are the nonpolar nature, which gives Hpid deposits and wettabdity problems and the tendency to adhere to the cornea. Efforts to modify the sdicone lens surface for improved wettabdity have achieved limited success. These efforts include grafting hydrophilic monomers, such as HEMA, GM (150), and NVP (151—153), to the lens surface and plasma treatments of finished lenses. Efforts to improve the movement of sdicone lenses on the cornea with various lens designs have not been successfld, and the cause of lens—cornea adherence, which is not an exclusive problem of sdicone lenses, is an active area of research. 

New templated polymer support materials have been developed for use as re versed-phase packing materials. Pore size and particle size have not usually been precisely controlled by conventional suspension polymerization. A templated polymerization is used to obtain controllable pore size and particle-size distribution. In this technique, hydrophilic monomers and divinylbenzene are formulated and filled into pores in templated silica material, at room temperature. After polymerization, the templated silica material is removed by base hydrolysis. The surface of the polymer may be modified in various ways to obtain the desired functionality. The particles are useful in chromatography, adsorption, and ion exchange and as polymeric supports of catalysts (39,40). 

In general, grafting of hydrophillic monomers have been found to lead to an increase in wettability, adhesion, dyeing, and rate of release of oil stains by detergent solution. On the other hand, if the monomer is hydro-phobic, the result will be decreased wetting by all liquids including oil stains. If grafting is not restricted to surface alone but encompasses the bulk of the backbone polymer, then the properties such as flame resistance, water sorption, crease resistance, etc. will be affected. 

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. 

A great variety of SAH was obtained using radical grafting of hydrophilic monomers on natural polymers without any previous modification Table 3 represents a short summary of the data on these SAH which can be divided into two groups. 

Nanogels made up of various intramolecularly cross-linked macromolecules have been prepared simply by performing the polymerization of hydrophilic monomers solubilized in the micellar core of reversed micelles, and they represent distinct macromolecular species from those obtained in bulk [191,240]. 

Dewatering surfactants can be polyoxyethylene, polyoxypropylene, and polyethylene carbonates [1348] or p-tert-amylphenol condensed with formaldehyde, or they can be composed of a copolymer from 80% to 100% alkyl methacrylate monomers and hydrophilic monomers [777]. Such a well treatment fluid may be used in both fracturing and competition operations to enhance and maintain fracture conductivity over an extended period of production. 

Emulsion breakers are made from acrylic acid or methacrylic acid copolymerized with hydrophilic monomers [148]. The acid groups of acrylic acid and methacrylic acid are oxalkylated by a mixture of polyglycols and polyglycol ethers to provide free hydroxy groups on the molecule. The copolymers are made by a conventional method, for example, by free radical copolymerization in solution, emulsion, or suspension. The oxalkylation is performed in the presence of an acid catalyst, the acid being neutralized by an amine when the reaction is complete. 

Table I summarizes conditions for the synthesis of two series of PDMAAm-1 -PIBs. The samples are identified by a code consisting of a letter and two numbers the letter (A) denotes the hydrophilic monomer DMAAm, whereas the two numbers indicate the Mn of the starting MA-PIB-MA (divided by 1,000) and the weight percent of PIB in the network (determined by elemental analysis). For example, A-4-26 denotes an amphiphilic network prepared with DMAAm as the hydrophilic moiety, containing a Mn=4,000 MA-PIB-MA, whose composition is 26% PIB.

In the most succinct sense, a hydrogel is simply a hydrophilic polymeric network cross-linked in some fashion to produce an elastic structure. Thus any technique which can be used to create a cross-linked polymer can be used to produce a hydrogel. Copolymerization/cross-linking free radical polymerizations are commonly used to produce hydrogels by reacting hydrophilic monomers with multifunctional cross-linkers. Water-soluble linear polymers of both natural and synthetic origin are cross-linked to form hydrogels in a number of ways ... 

Table 1 Nonionic, Hydrophilic Monomers Used for Hydrogel Synthesis... 

The first soft contact lenses were also constructed with a polymeric material containing a single monomeric unit. The added pliability of the soft lens was derived from the more hydrophilic nature of the monomer, enhancing the ability of the polymer to absorb water and provide greater comfort to the lens wearer. This monomer is a derivative of MMA known as hydroxyethyl methacrylate (HEMA). A number of hydrophilic monomers are used in soft lenses today these materials are referred to as hydrogels because of their ability to absorb significant amounts of water yet remain insoluble. 

KEY TERMS hydrophobic hydrophilic monomer cross-linking polymer copolymer hydrogel... 

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