HFIP

A number of HFIP-derived polyethers are known which exhibit good mechanical, thermal, and electrical properties (112,113). Aromatic polyethers have been synthesi2ed from bisphenol A (R = H) or AF (R = F) and fluorkiated aromatics (Ar = perfluorophenyl, perfluorobiphenyl, or... 

A polyester backbone with two HFIP groups (12F aromatic polyester of 12F-APE) was derived by the polycondensation of the diacid chloride of 6FDCA with bisphenol AF or bisphenol A under phase-transfer conditions (120). These polymers show complete solubkity in THF, chloroform, ben2ene, DMAC, DMF, and NMP, and form clear, colorless, tough films the inherent viscosity in chloroform at 25°C is 0.8 dL/g. A thermal stabkity of 501°C (10% weight loss in N2) was observed. 

The first HFIP-based polycarbonate was synthesi2ed from bisphenol AF with a nonfluorkiated aromatic diol (bisphenol A) and phosgene (121,122). Incorporation of about 2—6% of bisphenol AF and bisphenol A polycarbonate improved the dimensional stabkity and heat-distortion properties over bisphenol A homopolycarbonate. Later developments in this area concern the flame-retardant properties of these polymers (123,124). 

Several classes of polymers containing the HFIP-O group have been reported. These polymers show promise as film formers, gas separation membranes, coatings, seals, and other high temperature apphcations due to the properties imparted by this function, similar in many ways to the HFIP group. 

Synthesis and Properties. Several polymers containing HFIP-O groups have been investigated, the most common beeing epoxies and polyurethanes. The development of fluorinated epoxy resins and the basic understanding of their chemistry has been reviewed (127). 

Ethylene glycol oligomer SuperH2000 THE, HFIP containing TFA-Na... 

DMF, dimethylformamide DMSO, dimethyl sulfoxide HFIP, hexafluoroisopropanol LiBr, lithium bromide ODCB, o-dichlorohenzene TFA-Na, sodium trifluoroacetate THF, tetrahydrofuran. 

Polymethylmethacrylate is used with HFIP. Figure in parenthese is estimated value. 

The Shodex GPC HFIP series is packed with a hexafluoroisopropanol (HFIP) solvent. Engineered plastics, such as polyamides (nylon) and polyethylene terephthalate, were analyzed previously at a high temperature of about 140°C. Using FIFIP as an eluent, such engineered plastics can be analyzed at ordinary temperatures (Table 6.4). 

HFIP. -----, S mM CFsCOONa/HFIP. Flow rate 1.0 mL/min. Detector Shodex Rl. Column... 

FIGURE 6.19 Polyamide. Column Shodex GPC HFIP-80S + HFIP-803, 8 mm i.d. x 300 mm x 2. Eluent S mM CFaCOONa/HFIP. Flow rate 1.0 mL/min. Detector Shodex Rl. Column temp. 40°C. Sample 0.05%. SOO /iL. Poly(hexamethylene adipamide) (Nylon 66). 

In the case of functional polymers such as nylon, the molecular size can increase because ionic functional groups contained in the molecule repel each other. To decrease ionic repulsion, sodium trifluoroacetate should be added to HFIP. 

Controlling for these forces requires variation in the amount of salt, organic solvent, and the pFI of the mobile phase. It is impractical to perform such experiments with 50 mM formic acid an alternative additive must be used that maintains its chaotropic properties independent of salt content or pFI. Fortunately, mobile phases containing 50 mM hexafluoro-2-propanol (HFIP) afford a fractionation range comparable to that of the formic acid (Fig. 8.6), permitting the effects of these variables to be studied systematically. 

FIGURE 8.6 Comparison of hexafluoro-2-propanol (HFIP) with formic acid as a denaturing agent in SEC. Eiution positions of neutral amino acids were similar with both agents. The elution positions of Lys and Asp shifted dramatically in C, as shown by the tie lines, but this was an effect of pH (see Fig. 8.7). The elution positions of a-MSH and formic acid are shown to demonstrate that the amino acids eluted within Vo and V,. Column Same as Fig. 8.1. Flow rate 1.0 ml/min. Mobile phase As noted. Detection Aiij = 0.1 AUFS. 

FIGURE 8.7 Effect of pH on retention of amino acids. Column and flow rate Same as Fig. 8.1. Mobile phase 10 mA1 potassium phosphate with SO mM HFIP pH as indicated (adjusted prior to the addition of HFIP). 

PSS columns for fluorinated eluents PSS PFG columns were developed by PSS because users worldwide were unsatisfied with the stability of conventional organic SEC columns when running solvents such as hexafluroisopropa-nol (HFIP). Because polymeric gels tend to be unstable in fluorinated media, PSS modified silica to achieve better stability while maintaining perfect chromatographic performance. 

PSS SDV columns can be used for all applications requiring organic eluents. The exception to the rule is the exclusion of lower aliphatic alcohols (e.g. methanol) from the otherwise complete list (28). For fluorinated solvents such as TFE and HFIP, PSS recommends its specially designed PFG columns (cf. Section V1I,C), which have a much longer life in this kind of demanding eluents. Figures 9.13 through 9.19 show some unusual applications that illustrate the variety of solvents and the feasibility of the columns. 

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