Polymer swelling measurement

It is reasonably easy to use Eq. 26 to determine the solubility parameter of a solvent, but since the heat of vaporization of polymers is usually not known, other methods are needed to determine the solubility parameters of polymers. There are several experimental methods, based on polymer swelling measurements or on the determination of the intrinsic viscosity of polymer solutions. Alternatively, solubility parameters can be predicted from knowledge of the chemical structure of each component. The latter method is due to Small (72) and Hoy (73), who supplied values for molar attraction constants (G) of a large number of functional groups (Table 4). The constants G are additive. With these values it is possible to estimate the solubility parameter of any polymer using Eq. 28, where p represents the density and M the molecular weight of the polymer. 

The solubiHty parameter of a polymer is a measure of its iatermolecular forces, and provides an estimate of the compatibiHty of a polymer with another polymer or a polymer with a solvent. Two components are compatible if they have similar solubiHty parameters. The solubiHty parameter can be determined by various methods, such as intrinsic viscosity and swelling measurements. The solubiHty parameters of various polymers and solvents are tabulated ia refereace handbooks (146,147). It also can be estimated from the stmcture of the polymer (148). 

Product Identification was by GC/MS, NMR, and IR. Fundamental crosslinking chemistry was explored using swell measurements on simple solution copolymers and swell and tensile measurements with vinyl acetate (VAc), vinyl acetate/butyl acrylate (VAc/BA) or vinyl acetate/ethylene (VAE) emulsion copolymers. Polymer synthesis 1s described In a subsequent paper (6). Homopolymer Tg was measured by DSC on a sample polymerized In Isopropanol. Mechanistic studies were done 1n solution, usually at room temperature, with 1, 2 and the acetyl analogs 1, 2 (R =CH3). 

Volume swelling measurements have produced erratic results even under the most carefully controlled conditions. One important contribution in this regard is the work of Bills and Salcedo (8). These investigations showed that the binder-filler bond could be completely released with certain solvent systems and that the volume swelling ratio is independent of the filler content when complete release is achieved. Some thermodynamic problems exist, however, when such techniques are used to measure crosslink density quantitatively. First, equilibrium swelling is difficult to achieve since the fragile swollen gel tends to deteriorate with time even under the best conditions. Second, the solubility of the filler (ammonium perchlorate) and other additives tends to alter the solution thermodynamics of the system in an uncontrollable manner. Nonreproducible polymer-solvent interaction results, and replicate value of crosslink density are not obtained. 

Tablets coated with the Eudragit-PEG 400 mixture were made with three different polymer film thicknesses 6, 10 and 15 mg (KET-R, 10 and 15 tablets). For these tablets it was not possible to obtain swelling measurements because this was prevented by the lake coating.

The kinetic theory of rubber elasticity is so well known and exhaustively discussed (17, 27, 256-257, 267) that the remarks here will be confined to questions which relate only to its application in determining the concentration of elastically effective strands. In principle, both network swelling properties and elasticity measurements can provide information on network characteristics. However, swelling measurements require the evaluation of an additional parameter, the polymer-solvent interaction coefficient. They also involve examining the network in two states, one of which differs from its as-formed state. This raises some theoretical difficulties which will be discussed later. Questions on local non-uniformity in swelling (17) also complicate the interpretation. The results described here will therefore concern elasticity measurements alone. 

The n value may also be determined from swelling measurements of slightly cross-linked samples of the polymer (12). This method is based on a theory developed by Flory and Rehner (//). It does not require the polymer to be completely soluble in the plasticizer and avoids the need for osmotic pressure measurements which, even under the most favorable conditions, require considerable skill. 

The shear viscosity can be used for relating the polymer flow properties to the processing behavior, extruder design, and many other high shear rate applications. Elongational viscosity, die swell measurements as well as residence time effects can be estimated. Typical data are shown in Figure 6. 

Fiber optic sensors based on polymer swelling offer several potential advantages. They can be designed so that the optical measurement is separated from the polymer by a diaphragm so that the measurement can not be affected by the optical properties of the sample. Unlike fiber optic sensors based on indicator absorbance or luminescence, photodegradation is not a potential source of sensor instability. Measurements can be made in the near infrared region of the spectrum and take advantage of inexpensive components available for fiber optic communications. 

Methods of Measuring Polymer Swelling at Liquid Saturation... 

It must be concluded, therefore, that none of the above available methods is suited to serve as a standard protocol for an analytical study of polymer swelling. Fortunately, a convenient, easy to use, very reliable method and reproducible for measuring polymer swelling has been developed in the 3M laboratories as an offshoot of a product-oriented research effort. This method is discussed in the following section. 

Observed is the average value for the DVB mole fraction (x) in the polymer as determined by swelling measurements (Eq. 16) in 10 different liquids (including CHC13). 

Ph(CH2) Hliquidswithn > 3 (Fig. 28). Since methyl bromide is not a liquid at room temperature and atmospheric pressure (the conditions chosen for measuring polymer swelling), C, (empty circle in Fig. 30) was not determined experimentally but rather it was obtained by extrapolation of C for bromoform and methylenebromide and of Log oq, for the Br(CH2) H liquids to methyl bromide as described in Ref. 164. 

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