Copolymer gel

Organic cross-linkers, which include glyoxal (48) and formaldehyde (qv), have also been used. Use of hypohaUte salts (49) and epichlorohydrin (50) promotes gel stabiUty. Phenol—formaldehyde cross-linking systems have been used to produce stable acrylamide copolymer gels at temperatures above 75°C and brine hardness levels above 2000 ppm (51). 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermo sets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymerized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

Shodex has a wide variety of columns for organic GPC using organic solvents. The columns are packed with porous styrene-divinylbenzene copolymer gels especially developed for GPC use. Five types of standard-size GPC columns packed with different solvents are available. Downsized GPC columns are also available. 

The Shodex GPC KF-600 series is packed with 3- im styrene-divinylbenzene copolymer gels in a column having a volume of about one-third compared to standard-types of columns, which are best suited for reducing the organie solvents eonsumption, shortening the analysis time, and lowering the detection limit (Table 6.5). 

Hadden, DA, Master of Science Thesis, Florida State University, Tallahassee, FL, 1999. Hadden, D Rill, RL McFadden, L Locke, BR, Oligonucleotide and Water Self-Diffusion in Pluronic Triblock Copolymer Gels and Solutions by Pulsed Field Gradient Nuclear Magnetic Resonance, Macromolecules 33, 4235, 2000. 

The composition of a copolymer gel may also turn out to be significantly different from that of the starting mixture if the reaction does not go to completion and if all the sol is not incorporated into the network. This results from the differences in the reactivities of different monomers only in special cases are different... 

Vinyl alcohol copolymer gel is hydrophilic and has been developed for aqueous-phase size-exclusion liquid chromatography however, it is less polar than the polysaccharides. Its specificity permits the direct injection of a biological sample without deproteinization. For example, blood serum from a patient suffering from chronic nephritis has been injected directly as a measure of the degree of dialysis (Figure 3.17). Adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate in red blood cells have also been separated directly (Figure 3.18). Theophylline in blood serum has been... 

Conditions columns, Asahipak GS320 (vinyl alcohol copolymer gel), 50 cm x 7.6 mm i.d. eluent, 0.1 M sodium phosphate containing 0.3 M sodium chloride pH 7.0 flow rate, 1 ml min-1 detection, UV 250 nm direct injection of sample. Peaks l, protein, 2, orotidine 3, creatinine, and 4, uric acid. 

The separation of basic and metal-sensitive compounds is difficult on silica-based stationary phase materials, but these separations can be performed on vinyl alcohol copolymer gels. Examples are the separation of methallothionein from dolphin kidney, a-, j8-, and y-endorphin, and nucleotide and nucleoside mixtures.8 However, an analytical-scale separation may also be performed on surface-modified wide-pore silica gels (pore size 300 A or more), using columns which showed a negative response in the heavy metal test described above. 

Column, octadecyl-bonded vinyl alcohol copolymer gel, 10 cm x 6 mm i.d. eluent, 0.05 M sodium phosphate solution in 20% acetonitrile flow rate 1 ml min-1 temperature, 30 °C. Compounds 3C1, 3-chlorobenzoic acid and 4Et, 4-ethylbenzoic acid. 

Enthalpy can be measured by liquid chromatography where enthalpy is a slope of the relationship between In k and the inverse value of the absolute temperature. A schematic diagram is shown in Figure 6.7. The slope depends upon the solutes being retained by the same liquid chromatographic mechanism. An example is given in Table 6.4. The results, measured on an octadecyl-bonded vinyl alcohol copolymer gel, did not show a simple linear relationship. This is due to a conformation change of the octadecyl-bonded vinyl alcohol copolymer gel stationary phase material, which has a phase transition point at about 33 °C. 

Several improved stationary phase materials have been synthesized for reversed-phase liquid chromatography. One material is vinyl alcohol copolymer gel. This stationary phase is quite polar and chemically very stable however, it demonstrated a strong retention capacity for polycyclic aromatic hydrocarbons.45 9 Although stable octadecyl- and octyl-bonded silica gels have been synthesized from pure silica gel50,51 and are now commercially available, such an optimization system has not yet been built. Further experiments are required to elucidate the retention mechanism, and to systematize it within the context of instrumentation. 

Yoshida, R., Sakai, K., Okano, T., and Sakurai, Y. Modulating the phase transition temperature and thermo-sensitivity in iV-isopropylacrylamide copolymer gels, J. Biomater. Set Polymer Ed., 1994, 6, 585-598. 

A series of crosslinked copolymer gels composed of DMAEMA and AAm were prepared using methylenebisacrylamide as a crosslinker for the preparation of polymer membrane. The feed compositions for the polymer membranes are listed in Tables 1 and 2. The polymerization was carried out between two Mylar sheets separated by a rubber gasket (1-mm diameter) and backed by glass plates. After polymerization, the gel was immersed in distilled water for 3 days to remove unreacted compound. The thickness of gel membrane was 1 mm in swollen state (20°C). 

Based on the solution property of poly (DMAEMA-co-AAm) in response to temperature, the temperature dependence of equilibrium swelling of poly (DMAEMA-c6>-AAm) gel as a function of chemical composition was observed as shown in Figure 6. The transition temperature of copolymer gel between the shrunken and swollen state was shifted to the lower temperature with increases in AAm content in the gel network. This is attributed to the hydrogen bond in the copolymer gel network and its hydrophobic contribution to the LCST Copolymer II gel was selected as a model polymer network for permeation study because it showed the sharp swelling transition around 34°C. 

The molecular weight dependency of the spreading factor, in other words the restricted diffusion of the macromolecule in the pore Is much pronounced for styrene-divinylbenzene copolymer gel. 

Since the introduction of gel-permeation chromatography (GPC) in the 1960 s, there have been tremendous advances in polymer gel size-exclusion column technology. Polystyrene-divinyl benzene copolymer gels, and the techniques by which they are packed into columns, have improved to the point where commercial columns exhibit up to 50,000 plates/meter. These lO-ym gels are sufficiently rugged to permit flow rates of up to 3.0 ml/minute... 

Poly (NIPAAm) has been previously shown to have an LCST ca. 31-33 (21) while copolymers of NIPAAm and AAm have LCST s which rise as the AAm content increases (5, 7-9). At a sufficiently high content of AAm, the LCST phenomenon is no longer observed. Figure 2 illustrates the temperature dependence of relative gel water contents for copolymer gels of NIPAAm and AAm. The sharpest drop in water content with temperature is seen for the 100% NIPAAm gel. As the AAm content increases, the drop becomes flatter, and occurs at higher temperatures. 

Fig. 25. Polymerization of acrylonitrile by poly(methyl methacrylate) mastication. Analysis of products at various extent of polymerization, i free poly(methyl methacrylate) 2 soluble block copolymer 3 chloroform-insoluble block copolymer gel (78)...

Tanaka et al. studied the volume transition of IPAAm-(sodium acrylate) copolymers gel as a function of temperature for various copolymer compositions. Gels that had been swollen at lower temperatures underwent a sharp collapse at different transition temperatures, depending on the ionic composi-... 

Fig. 11. Temperature dependence of SANS intensity curves of NIPA/AAc copolymer gel (4> = 0.107)...

Annaka and Tanaka recently found the presence of several phases in polymer gels between the fully swollen and shrunken phases [46]. This interesting phenomenon was observed in a polyampholyte gel, consisting of acrylic acid (anionic constituent, AAc) and methacryl-amido-propyl-trimethyl-ammonium-chloride (cationic, M APT AC). The chemical structures of these constituents are shown in Fig. 32. A series of copolymer gels were prepared by radical copolymerization, where the total molar concentration of the constituents was kept constant at 700 mM and the molar ratio of AAc/MAPTAC was varied systematically. 

Fig. 33. Equilibrium swelling degree of d/do of copolymer gels made of various molar ratios of acrylic acid and MAPTAC in water as a function of pH at 25 °C. Acrylic add ami MAPTAC ratios of the gels are indicated in the diagram. For some gels there appear multiple phases for the same value of pH. They are reached by varying pH through different paths...

Fig. 34. Equilibrium swelling degree d/d erf copolymer gel made of 460 mM of acrylic acid and 240 mM of MAPTAC as a function of temperature at pH 7.2 (rightX and pH dependence (left) taken from Fig. 35...

Copolymer gels containing the following n-alkyl methacrylates were studied methyl (MMA), ethyl (EMA), propyl (PMA), n-butyl (BMA), and n-hexyl (HMA). Gels are identified in terms of the comonomer identities and motor contents. For example, MMA/DMA 70/30 indicates a gel consisting of 70 mol % MMA and 30 mol % DMA, with 0.1% w/w DVB. 

Swelling curves of NIPA-sodium acrylate (SA) copolymer gels have been measured [7] by the same method as applied to neutral gels using cylindrical samples. The concentration of NIPA (700-572 mM) and SA (0-128 mM) were... 

Fig. 9. Linear swelling ratio of NIPA-AA copolymer gel cylinders at 20 °C as a function of their diameter. The solid line is a guide for the eye. The dashed horizontal line denotes the value obtained on cubes and plates. (Reproduced with permission from Ref. 31)...

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