Poly dissolution kinetics

The dissolution behavior of P(la-aft-S02) was studied on QCM in a 0.21 N TMAH solution using thin films cast from ethyl lactate and baked at 130 °C for 60 sec. Figure 4 presents the dissolution kinetics curve of the polysulfone film. The 450-nm-thick film dissolved away in 0.15 sec, with an extremely fast dissolution rate of 30,000 A/sec, which was nicely observed by our QCM setup. The dissolution rate of poly(4-hydroxystyrene) (PHOST) in the same 0.21 N developer is in the range of 3000-200 A/sec depending on its molecular weight (27). Thus, the fiuoroalcohol polymer dissolves at least one order of magnitudes faster than PHOST, which was unexpected considering the similar pKa values of the fiuoroalcohol and phenol. In... 

The pathway and kinetics of the C to S transition have been studied on shear-aligned cylinders of the commercial diblock copolymer of PS and poly(ethylene-co-butylene) (KRATON G 1657 Shell Chemical Company) [143, 144], A complete dissolution of the cylindrical structure before the epitaxial... 

In a kinetic sense, the system is a better solvent than HFIP alone. We postulate that MeCl2 swells the amorphous regions of PET thereby providing HFIP with an easy access to the crystalline regions. This swelling action does not occur with HFIP alone, and the dissolution process takes much longer. At room temperature, amorphous PET is Instantaneously solubilized by this solvent system. PET that has been annealed for >24 hr at 220 C to yield maximum crystallinity dissolves in <4 hr at room temperature. PET annealed in this manner does not dissolve in pure HFIP after 14 days at room temperature. Poly(butylene terephthalate) and aliphatic polyamides are soluble in this solvent system. Polystyrene is also soluble, which permits conventional calibration and the use of the universal calibration approach. We have determined the Mark-Houwlnk relationships for PET and polystyrene in 70/30 MeCl2/HFIP to be... 

Three different ways have been developed to produce nanoparticle of PE-surfs. The most simple one is the mixing of polyelectrolytes and surfactants in non-stoichiometric quantities. An example for this is the complexation of poly(ethylene imine) with dodecanoic acid (PEI-C12). It forms a solid-state complex that is water-insoluble when the number of complexable amino functions is equal to the number of carboxylic acid groups [128]. Its structure is smectic A-like. The same complex forms nanoparticles when the polymer is used in an excess of 50% [129]. The particles exhibit hydrodynamic diameters in the range of 80-150 nm, which depend on the preparation conditions, i.e., the particle formation is kinetically controlled. Each particle consists of a relatively compact core surrounded by a diffuse corona. PEI-C12 forms the core, while non-complexed PEI acts as a cationic-active dispersing agent. It was found that the nanoparticles show high zeta potentials (approximate to +40 mV) and are stable in NaCl solutions at concentrations of up to 0.3 mol l-1. The stabilization of the nanoparticles results from a combination of ionic and steric contributions. A variation of the pH value was used to activate the dissolution of the particles. 

The amount of Si ions dissolution is found to be dependent on surface modification, which was confirmed by induchvely coupled plasma-atomic emission spectrometer (ICP-AES) analysis. Table 2.2 shows the dissolution amount of Si ions with and without surface modification of fumed silica slurry. Without surface modification, the amount of Si dissoluhon was 1.370 0.002 mol/L, whereas surfaces modified with poly(vinylpyrrolidone) (PVP) polymer yielded a dissoluhon of 0.070 0.001 mol/L, almost 20 hmes less than the unmodified surface. Figure 2.6 represents the electro-kinetic behavior of silica characterized by electrosonic amplitude (ESA) with and without surface modification. When PVP polymer modified the silica surface, d5mamic mobility of silica particles showed a reduchon from -9 to -7 mobility units (10 m /Vxs). Dynamic mobility of silica particles lacking this passivation layer shows that silica suspensions exhibit negative surface potentials at pH values above 3.5, and reach a maximum potential at pH 9.0. However, beyond pH 9.0, the electrokinetic potential decreases with an increasing suspension pH. This effect is attributed to a compression of the electrical double layer due to the dissolution of Si ions, which resulted in an increase of ionic silicate species in solution and the presence of alkali ionic species. When the silica surface was modified by... 

In a related study, Pitt and others (1979a) reported release rates of various steroids from monolithic films and capsules made from homopolymeric PCL, poly (D,L-lactide), and copolymers of caprolactone and D,L-lactide (in both 60/40 and 90/10 caprolactone/D,Lrlactide acid ratios), and copolymers of glycolic acid with D,L-lactide. The release rates of the steroids from the caprolactone-co-lactide polymers were similar to the homopolymeric PCL. However, the release rates from the glycolide-co-lactide polymers were much slower than those observed with PCL. Further data analysis revealed that the obseiv ed release kinetics depended upon the steroid dissolution rate (in the polymer) and the polymer cry stallinity. WTiile it is outside the scope of the current discussion, a good background reference on PCL thermodynamics and crystallinity is given by Lebedev (1979) and Chynoweth Stachurscki (1986). 

Effect of varying poly(styrene sulfonic acid) content in poly(vinylalcohol)-poly(styrene sulfonic acid) blend membrane and its ramification in hydro-gen-oxygen polymer electrolyte fuel cells were investigated. Imaging of the hydrogel formation during the dissolution was performed in a non-invasive way by means of the MRI. Water self-diffusion coefficients and water release kinetics of these materials have been characterized by NMR imaging technique, which validate the use of this membrane in polymer electrolyte fuel cells (PEFCs). 

Hashimoto, T., Kumaki, J., and Kawai, H. (1983) Time-resolved light scattering studies on kinetics of phase separation and phase dissolution of polymer blends. 1. Kinetics of phase separation of a binary mixture of polystyrene and poly(vinyl methyl ether). Macromolecules, 16 (4), 641-648. 

Owing to the oxophilicity of Al + ions all Al-MOFs contain Al-O bonds. In contrast to the large number of microporous zeolites in which the aluminmn ion in the framework is exclusively tetrahedrally surrounded, only octahedrally coordinated A1 atoms have been observed in Al-MOFs until now. The majority of the limited number of reported Al-MOFs is based on poly-carboxylic linker molecules although a few examples of porous aluminum phosphonates have been described in the literature. " The stability and the small number of Al-based MOFs stems from the same factors the high charge (-1-3) of the metal ion and the small ionic radius (r(CN = 6) 0.675 A). Hence dissolution of these MOFs in water is often kinetically hindered and at the same time they are almost... 

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