Swelling dissolution behavior

The thickening mechanisms of linear carboxyl-containing emulsion polymers have been studied in considerable detail. The polymer molecules of AST emulsions are initially in a coiled configuration within individual latex particles of submicrometer size, and the viscosity of the diluted latex emulsion is similar to that of water prior to neutralization. On the addition of base, the carboxyl groups are ionized, and hydrophilic polymer is formed within the particles. Depending on various factors, which will be elaborated on later in this chapter under the section entitled Factors Affecting the Swelling Dissolution Behavior of Conventional ASTs , the particles may only swell or dissolve completely, or the surface polymer may dissolve and leave swollen cores. 

Factors Affecting the Swelling Dissolution Behavior of Conventional ASTs... 

Many studies were conducted by various investigators to determine the effects of polymerization and other parameters on the thickening, swelling, and dissolution behavior of conventional ASTs. A listing of factors known to to have an effect in conventional AST emulsion thickeners (ASE) is given in List 1, and details concerning some of these are provided in the following discussion. 

List 1. Factors Known To Affect the Thickening, Swelling, or Dissolution Behavior of Conventional AST Emulsion Polymers (ASE Thickeners) ... 

Erosion is typically characterized by either occurring on the surface or in the bulk. Surface erosion is controlled by the chemical reaction and/or dissolution kinetics, while bulk erosion is controlled by diffusion and transport processes such as polymer swelling, diffusion of water through the polymer matrix, and the diffusion of degradation products from the swollen polymer matrix. The processes of surface and bulk erosion are compared schematically in Fig. 1. These two processes are idealized descriptions. In real systems, the tendency towards surface versus bulk erosion behavior is a function of the particular chemistry and device geometry (Tamada and Langer, 1993). Surface erosion may permit the... 

Some runs carried out under the same conditions but according to Procedure B gave the results represented by the points outside the curve, which indicate a higher conversion per hour. Such behavior might be explained by the fact that in the absence of water both swelling and dissolution of the elastomer into monomer are more rapid and complete hence, the subsequent dispersion of the reacting mass in water is favored. 

Gases interact with solids at high pressures, either by adsorption to crystal surfaces or by dissolution into amorphous materials, leading to volume changes. An experimental method to study the behavior of solids in the presence of dense gases has been developed. Sorption equilibria and solubilities are determined gravimetrically. Diffusion coefficients are derived with the help of suitable mass-transfer models. The swelling behavior of the solids is observed visually. 

In this chapter, we present results of the testing of a broad spectrum of polymers in carbon dioxide over a range of temperatures and pressures and evaluation of the effect of the high pressure carbon dioxide on the chemical/physical properties of materials tested. The testing was performed in a static manner with four controlled variables, namely temperature, pressure, treatment time and decompression time. The evaluation of the interaction of high pressure carbon dioxide with polymers included sorption and swelling behavior, solubility issue, plasticization and crystallization, and mechanical properties. The results of these evaluations are discussed in three sections Sorption, Swelling and Dissolution of Carbon Dioxide in Polymers at Elevated Pressure, Thermal Properties, and Mechanical Properties. ... 

In order to determine the appropriate operating conditions for the PET processing train, the dissolution and crys lization behavior of PET in NMP had to be studied. The dissolution rate of PET in NMP as a function of solvent temperature was established by measuring the mass loss of 2-liter bottle sections (two bottles) when exposed to NMP at various temperatures and times. The results of this study indicate that at 130°C the PET sections only swelled in the solvent, and did not dissolve appreciably even after over 4 hours in the solvent. At 140°C, however, the sections dissolved completely in less than 10 minutes. Figure 3 illustrates the linear increase in dissolution rate as temperature increases above 140°C (presented as % dissolved per... 

The stereoselective release behaviors of low-swelling molecularly imprinted polymer bead matrices in pressed-coat tablets were studied using either R- or S-propranolol selective MIPs. The in vitro release profiles of the low-swelling matrices showed a difference in the release of enantiomers, in that the nontemplate isomer was released faster than the template isomer. However, in the last phase of dissolution this difference was reduced and later reversed [64]. Stereoselectivity of release profiles for propranolol enantiomers were identified in MIP synthetic membranes from tablet formulations with significant differences between enantiomers [65]. Release of the enantiomer used as the print was always faster than the... 

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