Polymeric Solubility Profiles

Hansen [1] pioneered the classification of polymeric materials in terms of the three partial solubility parameters. The solubility parameters of many polymers may be found in standard references like Barton s handbooks [2,3]. Estimates of the polymer solubility parameters as determined from the group contribution theory based on chemical structure are also described in Barton s books. The most exact determinations utilize the solubility behavior of the polymer in a series of solvents with varying degrees of polarity and hydrogen bond character (hexane to water). Hansen first used this type of solubility 

A master list of solubility parameters for 166 resins and polymers is shown in Table 5.1. These values were derived from solubility studies, polymer swelling studies and estimated using the group contribution theory. This list is also contained in the spreadsheet data files discussed in Chapter 19. These values can be used to calculate the solvent-polymer radius of interaction values using Equation 5.1. 

In Equation 5.1 the i terms correspond to the parameters of the resin and the j terms to the parameters of the solvent. Since many of these polymers do not have a defined interactive radius R value one can use an average radius of 10 for the comparison of solvent-polymer interactions. Polymer solubility is a reasonable possibility if the calculated R value is less than 10. 

NUMBER SOLVENT DELTAD DELTAP DELTA H SOLV/POLY. RADIUS 

FigurO 5.1 Typical hydrogen bonding versus polarity plot that shows the relationship of solvent values to the polymer of interest. Plotting the polymer values on a x-y graph along with several solvents will many times suggest solvent blends for further evaluation. Source data compiled from the author s personal files. 

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There are now many synthetic polymeric materials available for film coating, many of which meet all the requirements of a good film former. These include lack of toxicity and a suitable solubility profile for film application and upon ingestion, together with the ability to produce a tough, yet elastic film even in the presence of powdered additives such as pigments. The film must, of course, be stable to heat, light, and moisture and be free from undesirable taste or odor. 

Two other amide-type solvents are the cyclic five-member heterocyclic 2-pyrrolidone and N-methyl 2-pymolidone. As shown in the solvent-resin solubility profile in Table 10.8 these two solvents dissolve a wide variety of resins. Both 2-pyiTolidone and N-methyl 2-pyirolidone are used as coalescent aids in floor polish formulations [11]. N-methyl 2-pyirolidone is an important component in many paint stripper formulations as well as a solvent for the removal of polymeric residues from reactor vessels. The solvent is used as a reaction medium for high molecular weight polymers, a synthetic fiber spinning medium, and as an aid in pigment dispersions. In the petrochemical industry N-methyl... 

Bergbreiter and coworkers (2/) recently described the development of a new polymeric support with interesting physical properties poly(/V-isopropyl-acrylamide) (PNIPAM). Several co- and ter-polymers containing PNIPAM have been successfully prepared. These materials exhibit an inverse temperature solubility profile in water. If heated above their lower critical solution temperature (LOST), they precipitate quantitatively from solution. Unlike a protein, PNIPAM derivatives do not denature. The LOST of the PNIPAMs can... 

Buccal dosage forms can be of the reservoir or the matrix type. Formulations of the reservoir type are surrounded by a polymeric membrane, which controls the release rate. Reservoir systems present a constant release profile provided (1) that the polymeric membrane is rate limiting, and (2) that an excess amoimt of drug is present in the reservoir. Condition (1) may be achieved with a thicker membrane (i.e., rate controlling) and lower diffusivity in which case the rate of drug release is directly proportional to the polymer solubility and membrane diffusivity, and inversely proportional to membrane thickness. Condition (2) may be achieved, if the intrinsic thermodynamic activity of the drug is very low and the device has a thick hydrodynamic diffusion layer. In this case the release rate of the drug is directly proportional to solution solubility and solution diffusivity, and inversely proportional to the thickness of the hydrodynamic diffusion layer. 

Compressed polymeric matrices provide a convenient method for achieving sustained release of highly water-soluble drugs [3-5]. Release profiles are usually analysed by equations derived by... 

The basic structure of a naphthalocyanine dye can be seen in Figure 6 (12). By varying the central atom Y, the organic (polymeric) group at the central atom, and the substituents Xw and X, an adjustment to the desired property profile, especially improved solubility, can be achieved. Naphthalocyanines with silicon as central atom evoke special interest, eg, the biaxially substituted silicon—naphthalocyanine (13) wherein the central Si bears two substituents and the rings are unsubstituted, ie, Xm = Xn = H. 

A number of patented technologies for multiparticulate dosage forms have been described recently, such as the Micropump system, which is an osmotically driven coated microparticle system designed to increase the absorption time for rapidly absorbed drugs.59 Combination of water-soluble and water-insoluble polymers could provide enhanced controlled release rates and profiles. A patented technology (COSRx) has been reported to be capable of delivering various sophisticated release profiles. The formulation involves a guar-gum-based tablet and a combination of water-soluble and water-insoluble polymeric tablet coat.60... 

Vinyl acetate is a colorless, flammable liquid having an initially pleasant odor which quickly becomes sharp and irritating. Table 1 lists the physical properties of the monomer. Information on properties, safety, and handling of vinyl acetate has been published (5—9). The vapor pressure, heat of vaporization, vapor heat capacity, liquid heat capacity, liquid density, vapor viscosity, liquid viscosity, surface tension, vapor thermal conductivity, and liquid thermal conductivity profile over temperature ranges have also been published (10). Table 2 (11) lists the solubility information for vinyl acetate. Unlike monomers such as styrene, vinyl acetate has a significant level of solubility in water which contributes to unique polymerization behavior. Vinyl acetate forms azeotropic mixtures (Table 3) (12). 

After completion of phase inversion, the polymer solution is dispersed in a 2-4-fold amount of water. Suspension aids used are water-soluble organic polymers, such as poly(vinyl alcohol) or polyvinylpyrrolidone, or inorganic compounds, such as Pickering systems. In order to achieve a final conversion of 99.5 %, initiator combinations with different decomposition times are used, and the polymerization follows a defined temperature-time profile. The suspension is then centrifuged, dried and compounded. 

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