The dynamics of macromolecules in ternary solutions consisting of a probe polymer, a matrix polymer, and a solvent are studied using dynamic light scattering (DLS) with refractive index matching and, as supporting techniques, static light scattering and viscometry. The probe is linear polystyrene (PS) of molecular weight 390 000, which was always present in dilute amounts. The matrix polymer is poly(n-hexyl isocyanate) (PHIC) of varying molecular weight and polydispersity, whose concentration ranged from dilute to semidilute. The solvents used are either 1,1,2,2-tetrachloroethane (TCE) or toluene. PHIC is completely isorefractive in TCE at 75.0 °C. At lower temperatures and in toluene it is nearly isorefractive, removing the direct contribution of the PHIC to the light scattering spectrum. DLS measurements of PHIC in chloroform show that the PHIC behaves as a wormlike chain with a persistence length of ~20 nm. Results from previous studies of PS in binary solution are used for comparison to its behavior in the ternary solutions, which contained varying amounts of PHIC. Ternary solution studies were conducted over a range of temperature from 25 to 75 °C. The translational diffusion coefficient of the PS in ternary solution decreases with increasing concentration of PHIC, but the overall dimension of the PS remains essentially constant for all solution conditions. The decrease in PS diffusion coefficient is smaller than that predicted by reptation. Comparison of the different fractions of PHIC shows that the translational diffusion coefficient of PS is affected by the flexibility of the PHIC. The PS diffusion coefficient for all the PHIC fractions depends on the end-to-end distance of the PHIC. A fast relaxational mode (not present in dilute PS solutions) was seen in the DLS spectra for samples above a certain onset concentration of PHIC. The amplitude of this relaxation is always a small portion of the DLS spectrum, ranging from Oto 5% of the total intensity. Using the contour length of the wormlike chain for the apparent rod length gives an onset concentration for the fast mode of CL3 10-15.The physical cause for this relaxation is unclear, although several possible explanations for it are discussed.
A comparison of calculated and measured glass transition temperatures of a series of three-component hydrocarbon blends was performed. The blends were prepared as mixtures of an elastomer with different proportions of tackifying resin and oil. Glass transition temperature, T g , was measured by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) at four measurement frequencies. Most of these blends had pressure-sensitive adhesive (PSA) properties, and were used to prepare a series of PSA tapes. The adhesion of the PSA tapes was shown to be strongly dependent on T g . Tack of PSA tapes was measured at two different temperatures, and shown to be directly correlated to the blend T g . Several predictive methods for blend T g that are based on individual component T g s were evaluated. The prediction of blend T g is far more accurate if the individual component T g values are determined by DMA instead of DSC. In addition, the Gordon-Taylor equation gave a significant improvement on predicted blend T g when compared to the Fox equation.
A key factor in designing a drug-in-adhesive transdermal drug delivery system is to understand the rate at which the drug and small-molecule excipients can diffuse in the adhesive matrix. The solubility of these components in the adhesive matrix is also of great importance. Results will be presented discussing the use of infrared-attenuated total reflectance (IR-ATR) spectroscopy as a method to measure both diffusion and solubility of small molecules in adhesives. In this method, the donor layer is either a doped adhesive or a free liquid that is placed in contact with a receptor layer which is an undoped adhesive in contact with an IR-ATR crystal. The IR-ATR crystal detects as a function of time any molecules that diffuse from the donor layer into and through the receptor layer.Examples will be discussed of several different experiments that can be performed with this technique. Diffusion coefficients are presented here for testosterone and terpineol in an isooctyl acrylate based adhesive using a doped adhesive donor layer. Diffusion and solubility of liquids in several adhesives has been determined using the experiment where a free liquid is used as the donor. Solubility and diffusion coefficients determined using an oversaturated doped layer containing dispersed, as well as dissolved solute, are presented here for testosterone and for progesterone. Finally diffusion from a doped layer of one adhesive to an undoped layer of a different adhesive was performed as a partition measurement. The parameters that can be extracted from each of these experiments, as well as the limitations of each type of experiment will be discussed.
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