Substituted cellulose ether

Substituted Cellulose Ethers. Since their introduction for ophthalmic use, MC and other substituted cellulose ethers such as hydroxyethylcellulose, hydroxypropylcel-lulose, hydroxypropyl methylcellulose (HPMC), and carboxymethylcellulose (CMC) have been used in artificial tear formulations.These colloids dissolve in water to produce colorless solutions of varying viscosity. They have the proper optical clarity, a refractive index similar to the cornea, and are nearly inert chemically. Their relative lack of toxicity, their viscous properties, and their beneficial effects on tear film stability have made cellulose ethers useful components of artificial tear preparations. Historically, the most frequently used representative of this group was MC. 

Over the years the other substituted cellulose ethers, particularly hydroxyethylcellulose and HPMC, have been more frequently used. They are somewhat less viscous than MC but possess cohesive and emollient properties equal or superior to those of MC. Like MC, these ethers also mix well with other polymers and substances present in artificial tear formulations and are compatible with... 

In addition to their use in tear substitutes, cellulose ethers are used to moisten contact lenses and, as... 

We have previously reported studies on the distribution of substituents in partially etherified celluloses which were prepared from heterogeneous alkali cellulose and from homogeneous nonaqueous cellulose solutions (21). In the latter case, partially substituted cellulose ethers such as methyl- and carboxymethyl-celluloses were prepared from SO2-DEA-DMSO solutions of cellulose by additions of powdered NaOH as a base. 

Frequently the polymers found in nature or made commercially need some improvements in their end-use properties for specific applications. In such cases, modification reactions can be made on the polymers. A notable case is cellulose, which is insoluble in water and in most organic solvents. Suitable reactions are done industrially to convert it to esters or ethers. Sachinvala et al. have synthesized a number of di- and tri-substituted cellulose ethers and characterized them by NMR (64). Xu et al. have used 2D NMR to analyze ethyl cellulose, a commercial polymer (65). Newmark has used 2D NMR to study cellulose acetate butyrate (54). Other uses of NMR to study polymer reactions have been reviewed elsewhere (129). 

Synthesis, Physical, and NMR Characteristics of Di-and Tri-Substituted Cellulose Ethers... 

A number of water-soluble cellulose ethers are marketed." Methyl cellulose is prepared by a method similar to that used for ethyl cellulose. A degree of substitution of 1.6-1.8 is usual since the resultant ether is soluble in cold water but not in hot. It is used as a thickening agent and emulsifier in cosmetics, as a paper size, in pharmaceuticals, in ceramics and in leather tanning operations. 

Occasionally, water-soluble plastics are required. Poly(vinyl alcohol) is commonly the first to be considered but some cellulose ethers, polyethylene oxides, poly(vinyl pyrrolidone) and A-substituted polyamides are among many possible alternatives. 

Semisynthetic gels are also very useful for the creation of drug delivery systems. Cellulose ethers are particularly important in drug delivery. These compounds are made by derivatizing the cellulose hydroxyls with various groups such as hydroxypropyl, methyl, or carboxymethyl. This substitution breaks up the crystallinity of native cellulose and makes it water-soluble [23], The degree... 

Cellulose ethers of a high degree of substitution are stable, relatively nonflammable, resistant to ultra-violet light and compatible with a wide range of solvents and plasticizers. Certain ethers of a low degree of substitution are soluble in water or alkali. It would appear from these properties that cellulose ethers should be ideally adapted for use in the plastics field and for many other uses. 

Nonionic cellulose ethers, hydroxyethyl(HE) and hydroxypropy1 (HP) cellulose, of variable molar substitution (M.S.) levels, were adsorbed on peptized sodium montmorillonite surfaces from fresh and saline (NaCl) aqueous solutions. The amounts adsorbed for 2 M.S. HEC and HPC and 4 M.S. HEC were insensitive to electrolyte concentration the 4 M.S. 

Most of the selective-etherification studies on polysaccharides have been made with cellulose, and nearly all of them have involved quantitative separation of the D-glucose derivatives formed on hydrolysis of the partially substituted celluloses. In view of their stability, ethers of polysaccharides are particularly suited to this approach. 

A new class of water-soluble materials [10,11], was developed as a result of such design parameters that will be referred to as double substituted cationic cellulose ethers (DCEs). These materials contain both a cationic substituent and a hydrophobic substituent, attached to a cellulose ether backbone. The use of a double-substituted hydrophobe modified cationic polysaccharide is fundamentally different from current commercial vaginal formulations, which rely exclusively on nonionic or anionic vehicles. 

Uses Manufacture of nylon solvent for cellulose ethers, fats, oils, waxes, resins, bitumens, crude rubber paint and varnish removers extracting essential oils glass substitutes solid fuels fungicides gasoline and coal tar component organic synthesis. 

These considerations sparked our investigation into the possibility of producing responsive polymer gels from cellulose ether polymers. Cellulose ethers are alkyl-substituted cellulose derivatives which are on the FDA s GRAS list for use in food and pharmaceutical formulations. Since most cellulose ethers display lower critical solution temperatures (LCST), as gels they should be temperature... 

Lindsey andco-workers [27,69,70], Weglarz and Atkin [32], and Metivier and co-workers [31,81] have all developed and applied Zymark robotic workstations to optimize chemistry. Lindsey and co-workers [69] completed a factorial design study (16 experiments) to examine the role of catalyst and reactant concentrations on porphyrin yield in less than 1 day of workstation time. Weglarz and Atkin at Dow Chemical Company [32] studied the effect of reaction parameters on (i) the alkoxy substitution of cellulosic ethers (ii) the base-catalyzed conversion ofphenethyl bromide to styrene and (iii) the onset of crystallization employing a fiber optic probe. Metivier and co-workers at Rhone-Poulenc [31,81] focused on the evaluation of catalysts, reagents, and solvents for process optimization work of numerous proprietary reactions. 

Mention has already been made of the numerous effects attendant upon chemical substitutions on the polysaccharide linear chain. Natural branches impart a dispersion stability to amylopectin that is not afforded amylose. One only has to compare cellulose ethers, deesterified chitin, and the lysis product of protopectin with the underivatized parent compound to appreciate the impact of chemical substituents on functionality. The loosening of compact, parallel structures with alkyl, hydroxyalkyl, and alkoxyl groups facilitates hydration and transforms insoluble, refractory polysaccharides to soluble, reactive polysaccharides. Not only do these substituents obstruct the crystallization tendency, they almost always confer secondary functionalities like q enhancement and foam, suspension, and freeze-thaw stabilization. 

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