Casting tetrahydrofuran

A number of studies have recently been devoted to membrane applications [8, 100-102], Yoshikawa and co-workers developed an imprinting technique by casting membranes from a mixture of a Merrifield resin containing a grafted tetrapeptide and of linear co-polymers of acrylonitrile and styrene in the presence of amino acid derivatives as templates [103], The membranes were cast from a tetrahydrofuran (THF) solution and the template, usually N-protected d- or 1-tryptophan, removed by washing in more polar nonsolvents for the polymer (Fig. 6-17). Membrane applications using free amino acids revealed that only the imprinted membranes showed detectable permeation. Enantioselective electrodialysis with a maximum selectivity factor of ca. 7 could be reached, although this factor depended inversely on the flux rate [7]. Also, the transport mechanism in imprinted membranes is still poorly understood. 

Brittle colorless films of PBPP may be cast from tetrahydrofuran solution. The insoluble portion of PBPP is swelled by the tetrahydrofuran and gives rise to free-standing films on solvent evaporation. Differential scanning calorimetry experiments on PBPP show a glass transition temperature at 40 °C, and some indication of a melting transition at 170° C. 

Tetrahydrofuran has been reported to exhibit an absorption maximum at 280 nm (52,56), but several workers have shown that this band is not produced by the purified solvent (30,41,57). Oxidation products from THF have been invoked in order to account for the appearance of the 280-nm band in PVC films that are solvent-cast from THF in air (57. 581. However, in some reported cases (56,59), this band was undoubtedly produced, at least in part, by a phenolic antioxidant (2.6-di-tert-butyl-p-cresol)(59) in the solvent. Since certain -alkylphenols have now been shown to be powerful photosensitizers for the dehydrochlorination of PVC (60), it is clear that antioxidant photosensitization might well have been responsible for some of the effects attributed previously (56) to THF alone. On the other hand, enhanced rates of photodegradation under air have also been observed for PVC films cast from purified THF (57), a result which has been ascribed to radical formation during the photooxidation of residual solvent (57,61). Rabek et al. (61) have shown that this photooxidation produces a-HOO-THF, a-HO-THF, and y-butyro-lactone, and they have found that the hydroperoxide product is an effective sensitizer for the photodehydrochlorination of PVC at X = 254 nm (61). 

Materials. PVCz (Takasago International Co. Ltd.) was purified by several reprecipitations froa benzene-methanol solution. 1-Ethylpyrene (EPy) was recrystallized and sublined in vacuo before use. PMMA was reprecipitated twice froa tetrahydrofuran solution with nethanol. PVCz films were prepared by spin-coating a 10 wtX anisole solution of the polyner on a quartz plate. PMMA and EPy were dissolved in chlorobenzene and cast on quartz or sapphire plates. 

Analysis of S-SEBS by SAXS has revealed the presence of cylindrical morphologies for a degree of sulfonation of <34%. Interestingly, different morphologies can also be observed when membranes are cast from different solvents. Membranes (27 mol% degree of sulfonation) cast from THE form lamellar morphologies, as seen in Figure 3.27, while those cast from MeOH/ THE (tetrahydrofuran) (20/80 v/v) exhibit a diffusive phase boundary with disorderly interconnections between domains. This is due to the differences... 

For example, in Figure 3 it is demonstrated that tetrahydrofuran (THF) and formamlde can be mixed AO 60 to establish a cosolvent as designated. Recognition of this fact makes it possible to explore a number of casting solutions which, because they contain a volatile component, do not require the difficult evaporation procedures discussed above. In addition, it is possible to explore a number of non-classical or novel casting solutions as will be demonstrated below. 

Polyurethane synthesis. PU films were synthesized by pre-polymerization of all starting materials in tetrahydrofuran solution at room temperature followed by solution casting as described previously (6). Dibutyltin dilaurate was used as catalyst (2% of total sample weight). The PU films obtained were cured for 35 hours at 95 1°C. 

Methods. Polyblend samples were prepared by solution casting from tetrahydrofuran (THF), or chloroform or by injection molding using a Mini-Max Molder by Custom Scientific Instruments. Specific experimental details are given elsewhere (9,10,11). 

Methods. Individual solutions of the blend components in dioxane (or tetrahydrofuran) were mixed, and stirred for about 12 hours before casting into a Teflon mold. Solvent evaporation proceeded under ambient conditions for 24 hours followed by transferral to a vacuum oven at 60°C for further removal of solvent. The dried blends were then stored in a vacuum desiccator over P2O5. 

From the solutions of polyimides in tetrahydrofuran (THF) strong, flexible and colourless films can be cast. Pressing of the polyimides carried out at temperatures 100 °C higher than Tg and 10 MPa leads to the formation of yellowish transparent moulded articles. 

The blend of poly(bisphenol A carbonate)-(poly(caprolactone) PC-PCL is particularly unusual in that both polymers are capable of crystallization and FT-IR has been used to study the state of order in these blends as a function of the method of preparation 254,255). In this case, PCL is a macromolecular plasticizer for PC. The PCL becomes progressively less crystalline as the concentration of PC increases. PC is amorphous if the blend is cast from methylene chloride but semicrystalline if cast from tetrahydrofuran. When PC in the pure form is exposed to acetone, it will not crystallize, but in the blend, exposure of acetone causes the PC to crystallize which emphasizes the additional mobility of the PC in the blend. 

Sheets of Kraton 102 were prepared by casting from solution in benzene, cyclohexane, and tetrahydrofuran. The lower (1,4-polybutadiene) transition temperature was —88°C for all samples by differential thermal analysis (DTA) on a duPont thermal analyzer at a heating rate of 5°C/ minute. The upper transition temperature of the triblock could not be... 

The relaxation measurements on sheets cast from cyclohexane solution were made in the same way at 15 temperatures from —70° to 80°C. Two sheets were cast from tetrahydrofuran solution. Relaxation measurements were made at 4% strain at 10 temperatures between —70° and 70°C, and at 8% strain at 9 temperatures between —70° and 70°C. 

Figure 1 shows a plot of the reduced tensile relaxation modulus, Ep(t), against the time, t, in logarithmic coordinates for Kraton 102 cast from benzene. Similar plots were prepared for the results obtained on specimens cast from cyclohexane and tetrahydrofuran solution, respec-... 

Figure 2. Master curves of the tensile relaxation modulus, E0(t), of Kraton 102 cast from benzene, cyclohexane, and tetrahydrofuran solutions, as a function of time, t, at 30°C...

Figure 6 for the creep data, using 0°C as the reference temperature. The shift factors obtained from creep data on Sheets I and II are plotted on the same curve, within experimental error, although the two sets of data did not superpose well with each other. The same is true for the data at 2 and 4% strain on specimens cast from tetrahydrofuran solution. Quite generally, data could only be shifted with respect to each other when they were derived from the same sheet. 

Figure 13.6 Film cast from a 1 2 mixture of poly(styrene-co-butadiene) and poly(2-vinyl pyridine-co-butadiene) with about 15 mol% butadiene content (10 wt% solution of the copolymers in tetrahydrofuran). Dark areas, poly(styrene-co-butadiene) light areas, poly (2-vinyl pyridine-co-butadiene) [15]. Courtesy of Dr A. Schindler...

Membrane-casting Techniques. Uhtil recently, PVC membranes have been exclusively formed by solvent casting techniques but which are not well-suited to the fabrication of ISFET devices. Membrane components in tetrahydrofuran are difficult to manipulate on a micro scale and are prone to absorb atmospheric moisture, thus weakening the adhesion at the sensor-ISFET interface. Che innovation which dispenses with the tetrahydrofuran casting stage is based on an in situ photolysis of the model calciun sensor cocktail admixed with monobutyl methacrylate + benzoyl peroxide + benzoin methyl ether at 340 nm (3). Hie resultant matrix adhered well to the ISFET gate and its potentiate trie response compared favourably with the analogous P and P2-MPMA ISE (Table II). 

Braun and co-workers [46] reported that reductive dechlorination of PVC using tri-n butyl tinhydride ( -Bu3SnH) leads to vinylchloride-ethylene copolymers. Copolymers were characterised by casting film from tetrahydrofuran (THF) solution in a potassium bromide disk. It is thought that the IR absorption peak at 750 cm"1 is ascribed to the (CH2)3 sequences and the peak at 720 cm"1 is due to the (CH2)n>5 sequences. As the dechlorination starts, the peak at 750 cm"1 due to CH2 sequences appears and intensifies with reaction time. The intensity of the peaks at 690 and 615 cm"1 due to the C-Cl stretching vibration slowly decreases. If the reduced PVC contains more than 46 wt% chlorine, only the absorption peak at 750 cm"1 appears in the IR spectra. If the chlorine content is less than 46 wt%, the peak at 720 cm"1 weakens. In this case the (CH2)n>5 sequences become more prominent than the -(CH2)3-sequences [46]. 

Other Transient Interactions. The PVA/borax example dealt with the effects of surface exposure of a two-component polymer system to a wetting liquid. We discovered a practical example of this class of phenomena in a plasticized poly (vinyl chloride) (PVC) system. A peculiar plasticizer (tetraethyl methylene bisphosphonate) for PVC has been found (6) which has the unusual property of exuding out of PVC immediately upon exposure to high humidity. The plasticizer quickly re-enters the resin when the humidity is reduced. A film of 60% resin and 40% plasticizer was solvent cast from tetrahydrofuran onto an impedometer bar and was subjected to sudden high humidity exposure. 

Chen et al. (67) reported the use of trifluoroacetic acid (TFA) as a cosolvent with tetrahydrofuran (THF) to improve dispersion and processability of the nanocomposites. They prepared MWCNT-PMMA composite films with varying CNT content by solvent casting method using 10 vol % TFA as a co-solvent with tetrahydrofuran (THF). SEM and optical microscopy revealed a good dispersion of nanotubes in solvent and PMMA. The composites showed low percolation... 

The resulting HS-polymers are colorless powder solnble in tetrahydrofuran and esters as well as aromatic hydrocarbons snch as tolnene, xylene and mesitylene. The HS-polymers can be cast into a transparent and flexible fihn as seen in Fig. 5. 

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