Polymers, dissolution

Use well-designed, specialized polymer dissolution systems wherever possible (such as those from the U.S. Filter, Inc. subsidiary, Strandco ), especially for emulsion polymers, rather than simple dissolving tanks and mixers with propeller-type impellers. This prevents undissolved lumps of polymer (fish-eyes) and the breakdown of polymer chains. Always install a strainer to prevent possible pump clogging. 

From a reaction engineering viewpoint, semiconductor device fabrication is a sequence of semibatch reactions interspersed with mass transfer steps such as polymer dissolution and physical vapor deposition (e.g., vacuum metallizing and sputtering). Similar sequences are used to manufacture still experimental devices known as NEMS (for nanoelectromechanical systems). 

Narasinham, B Peppas, N, A, The Physics of Polymer Dissolution Modeling Approaches and Experimental Behavior, Vol, 128, pp. 157-208,... 

Table 3.4 summarises the main characteristics of a variety of sample preparation modes for in-polymer additive analysis. Table 3.5 is a short literature evaluation of various extraction techniques. Majors [91] has recently reviewed the changing role of extraction in preparation of solid samples. Vandenburg and Clifford [4] and others [6,91-95] have reviewed several sample preparation techniques, including polymer dissolution, LSE and SEE, microwave dissolution, ultra-sonication and accelerated solvent extraction. 

Applications The majority of SFE applications involves the extraction of dry solid matrices. Supercritical fluid extraction has demonstrated great utility for the extraction of organic analytes from a wide variety of solid matrices. The combination of fast extractions and easy solvent evaporation has resulted in numerous applications for SFE. Important areas of analytical SFE are environmental analysis (41 %), food analysis (38 %) and polymer characterisation (11%) [292], Determination of additives in polymers is considered attractive by SFE because (i) the SCF can more quickly permeate throughout the polymer matrix compared to conventional solvents, resulting in a rapid extraction (ii) the polymer matrix is (generally) not soluble in SCFs, so that polymer dissolution and subsequent precipitation are not necessary and (iii) organic solvents are not required, or are used only in very small quantities, reducing preparation time and disposal costs [359]. 

Oligomeric hindered amine light stabilisers, such as Tinuvin 622 and Chimassorb 944, resist satisfactory analysis by conventional HPLC and have required direct UV spectroscopic analysis of a polyolefin extract [596], PyGC of an extract [618,648], or SEC of an extract [649]. Freitag et al. [616] determined Tinuvin 622 in LDPE, HDPE and PP by saponification of the polymer dissolution in hot toluene via addition of an... 

Lawrence and Ducharme [489] have described a fast, simplified method for the detection of fluorescent whiteners in polymers, in which the polymer dissolution was applied directly to the thin layer. Also the separation of optical brighteners (Leucopur EGM, Azur 4, Azur 5, Hostalux ABC, Uvitex OB, Eastobrite OB) from plastics and migration into water and olive oil was studied by HPTLC on RP-18 silica using various mobile phase mixtures and UV detection [490]. 

Table 7.90 Main features of (tSEC-GC analysis of polymer dissolutions...

When dissolved in more saline waters, xanthan gum produces a higher apparent viscosity than the same concentration of polyacrylamide (292). Prehydration of xanthan in fresh water followed by dilution in the saline injection water has been reported to provide higher viscosity than direct polymer dissolution in the same injection water. Optical rotation and intrinsic viscosity dependence on temperature indicate xanthan exists in a more ordered conformation in brine than in fresh water (293). 

C.J. Mcneil, D. Athey, M. Ball, W.O. Ho, S. Krause, R.D. Armstrong, J.D. Wright, and K. Rawson, Electrochemical sensors based on impedance measurement of enzyme-catalyzed polymer dissolution theory and applications. Anal. Chem. 67, 3928-3935 (1995). 

It is important to distinguish between erosion and degradation. Erosion is mass loss from a bioerodible polymer and may be a consequence of polymer dissolution or degradation of the polymer backbone, followed by dissolution of the degradation products. Degradation typically occurs by hydrolysis of the polymer backbone, the kinetics of which is a function of the polymer chemistry. Thus, erosion is the sum of several elementary processes, one of which may be polymer degradation. 

Model of Dissolution. Based on the results described above, a model for the dissolution of phenolic resins in aqueous alkali solutions 1s proposed. The model 1s adapted from Ueberrelter s description for polymer dissolution 1n organic solvents (.21). In Ueberrelter s model, the dissolution process takes place 1n several steps with the formation of (a) a liquid layer containing the dissolved polymer, (b) a gel layer, (c) a solid swollen layer, (d) an infiltration layer, and (e) the unattacked polymer. The critical step which controls the dissolution process is the gel layer. In adapting h1s model to our case, we need to take into account the dependence of solvation on phenolate ion formation. There 1s a partition of the cation and the hydroxide ion between the aqueous solution and the solid phase. The... 

The electrostatic interactions between the ions when dissolved in the polymer are a legacy of the electrostatic interactions which existed in the crystalline salt. As a result of the persistence of strong ion-ion interactions when a salt is dissolved in a polymer, dissolution may be regarded as a process in which some of the electrostatic interactions (bonds) between ions in the salt are replaced by interactions between the cation and the polymer. 

Drug release from soluble polymers is accompanied by the gradual erosion-type dissolution of the polymer. Therefore, polymer dissolution and drug diffusion may be the overall hybrid mechanism of release. Drug release from nonsoluble hydrogels generally follows Fickian or non-Fickian diffusion kinetics [51]. The mechanism of... 

When mixtures of solvents of different density are used for polymer dissolution, an equilibrium is established during ultracentrifugation where the concentration of the solvent of higher specific gravity is increased at the bottom of the cell... 

Kwon and coworkers described solid polyelectrolyte complex systems which dissolve rapidly in response to small electric currents. The solid doses were based on poly(ethyl oxazoline) and poly(methacrylic acid) with a repeating unit stoichiometry of 1 1. Insulin was released in response to slight electric currents due to electrically induced polymer dissolution [380]. In similar work Kwon and coworkers [381] studied release of edrophonium chloride and hydrocortisone from poly(2-acrylamido-2-methylpropane sulfonate-co-n-butyl methacrylate). An on/oflf mechanism of the edrophonium chloride release was observed and was attributed to ion exchange of solute and hydroxonium ion. The cationic solute release was assisted by electrostatic forces, whereas release of the neutral hydrocortisone solute was only affected by swelling and deswelling. 

To facilitate polymer dissolution, a magnetic heating and stirring unit may be used. Be careful to keep the temperature less than the boiling point of the solvent. Allow solution to return to room temperature before proceeding to step 7. 

Bioerodible alkyl monoesters of poly(vinyl methyl ether-maleic anhydride) (PVM-MA) (Fig. 1) can be used to control drug release. Being acidic, ionizable polymers the pH of the disolution medium affects the rate of polymer dissolution [1]. 

During polymer dissolution, the pH on the polymer surface decreases. This decreases the rate of polymer dissolution. When buffer is added to dissolution medium, hydrogen ions are neutralized by the buffer on the surface of the polymer. The buffer concentration thus affects the rates of polymer dissolution and erosion-controlled drug release [1]. In biological fluids with poor... 

In vivo results correspond quite well to those of the in vitro experiments although the effect of a basic additive seems to be greater in vivo. It is possible to increase the dissolution rate of PVM-MA esters in tear fluid by adding disodium phosphate or possibly other basic salts to the matrices. With basic additives it may be possible to modify drug release and polymer dissolution also in the case of other polyacids. 

J.Heller, R.W.Baker, R.M. Gale and J.O.Rodin, Controlled release by polymer dissolution I. Partial esters of maleic anhydride copolymers—properties and theory, J. Appl. Polym. Sci, 22,1991 (1978). 

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