Styrene copolymers column temperature

Fig. 10. Copolymer separation. Gradient elution of the mixture of seven poly(styrene-co-methyl methacrylate) samples on a silica column (150x4.6 mm d0 = 6 nm dP = 5 pm). Gradient iso-octane/(tetrahydrofuran +10% methanol), 10% B (0 min), 50% (8 min), 80% (10 min), 100% (11 min) flow rate 1 ml/min, reduced to 0.3 ml/min after 9.9 min. Methyl methacrylate content (wt %) indicated. Molar mass values 11.4 — 160 kg/mol 23.8 — 250 37.0 — 150 49.5 — 185 64.0 — 235 76.2 — 220 88.5 — 220. Column temperature 50 °C. (By courtesy of Elsevier Science Publ. [43])...

Chromatographic System Determine as directed under Chromatography, Appendix HA, but use a liquid chromatograph equipped with a differential refractometer detector and a 30-cm x 7.8-mm (id) column packed with 25-pm diameter beads of silver bonded to sulfonated divinyl benzene-styrene copolymer (Aminex HPX-42A, Bio-Rad Laboratories, or equivalent). Maintain the column at a constant temperature of 65° 10°, and the flow rate at 0.3 to 1.0 mL/min. Use deionized water as the mobile phase. 

Chromatographic System Use a liquid chromatograph equipped with a refractive index detector that is maintained at a constant temperature and a 9-mm x 30-cm column packed with a strong cation-exchange resin, about 9 pm in diameter, consisting of sulfonated cross-linked styrene-divinylbenzene copolymer in the calcium form (Aminex HPX-87c, or equivalent). Maintain the column temperature at 85° + 0.5°, and the flow rate of the Mobile Phase at about 0.5 mL/min. Chromatograph the Standard Preparation, and record the peak responses as directed under Procedure. Replicate injections show a relative standard deviation not greater than 2.0%. 

Methods of Separation. Elution Behavior. First, elution was performed by an isocratic elution mode. At a constant column temperature, the copolymers and homopolymers of polymethacrylates and polyacrylates were retained in the column with chloroform (and DCE) without ethanol. Only polystyrene could elute from the column. By adding ethanol to chloroform (and DCE), copolymers with a higher styrene content started to elute, and by increasing the ethanol content in the mobile phase, copolymers with less styrene were eluted. 

For example, at a column temperature of 10 °C, poly(styrene-methyl methacrylate) P(S-MMA) copolymer with 48.7% styrene was retained in the column with chloroform-ethanol (99.5 0.5) and eluted 100% from the column with the mobile phase containing more than 1.5% ethanol (7) (Figure 1). At the mobile phase of chloroform-ethanol (99.0 1.0), half of the copolymer was retained in the column and the... 

The copolymers tend to adsorb on the column at a higher column temperature, and copolymers with a higher methacrylate or acrylate component required a lower column temperature for elution. For example, a P(S-MMA) copolymer with 66.3% styrene eluted 100% from the column at column temperatures 10-30 °C with the mobile phase of chloroform-ethanol (99 1) and was retained in the column at 50 °C (Figure 2). The reason for the observation in Figure 2d was the same as that in Figure Ic. Lower column temperature (and/or a higher ethanol content in the mobile phase) was preferable for the elution of the copolymers having less styrene. 

Mechanisms of Retention and Elution. These results can be summarized as follows the copolymers tend to adsorb in the column at a higher column temperature and at a lower content of ethanol in the mobile phase and the copolymers with a lower styrene component require a lower column temperature or a higher content of ethanol in the mobile phase to elute from the column. The ethanol content in the mobile phase or a column temperature did not affect peak retention volume for the copolymers. All the copolymers eluted at the same retention volume. 

A - poly butadiene styrene copolymer B - polybutadiene a-methyl styrene copolymer. Sample heating rate 10 °C/min GC column SE-30 column temperature 150 °C. 

Figure 12.9 Typical pyrolysis chromatogram of fraction from a styrene-acTylonitiile copolymer sample obtained from a miciocolumn SEC system 1, acrylonitrile 2, styrene. Conditions 5 % Phenylmetliylsilicone (0.33 p.m df) column (50 m X 0.2 mm i.d.) oven temperature, 50 to 240 °C at 10 °C/min carrier, gas, helium at 60 cm/s flame-ionization detection at 320 °C make-up gas, nitrogen at a rate of 20 mL/min. P indicates tlie point at which pyrolysis was made. Reprinted from Analytical Chemistry, 61, H. J. Cortes et ai, Multidimensional cliromatography using on-line microcolumn liquid cliromatography and pyrolysis gas cliromatography for polymer characterization , pp. 961-965, copyright 1989, with permission from tlie American Chemical Society.

SEC stationary phases are usually composed of reticulated organic polymers (styrene-divinylbenzene copolymers) or minerals (hydroxylated silica) that are used as beads with diameters of 5 10 pm. Pore diameters, which can be varied during fabrication, are within the 4- 500 nm range. These materials, often called gels, must withstand the pressure drop across the column and temperatures in the order of 100 °C in order to allow their utilisation under various conditions. Standard columns have a length of approximately 30 cm (ID = 7.2 mm). 

For the method development of the SEC separation, the main attention should be focused on the suppression of analyte interactions with the surface of packing material. This usually requires a careful selection of the SEC column. In GPC, commercially available synthetic organic polymer columns are usually packed with styrene-divinylbenzene copolymer particles, which are only capable of weak dispersive interactions. Any possible analyte interactions with the surface could be suppressed by using a strong solvent, which will be preferentially adsorbed on the packing material surface. Selection of such a solvent is limited since the polymer solubility in that particular solvent needs to be considered. Tetrahydrofuran is the most common solvent used for most GPC separations, although for polyimids and other high-temperature polymers the use of special solvents such as n-methylpyrrolidone may be necessary. 

The treatment of alkaline, crude polyether polyols with strongly acidic cation exchange resins (copolymer of styrene - divinylbenzene with sulfonic acid groups) is a very efficient purification method. The treatment is performed at moderate temperatures (for example 50-70 °C) in the presence of water or, better still, in the presence of a solvent such as methanol or a methanol-water mixture. The treatment may be static (by mixing the crude polyether with cation exchange resin in a reactor, followed by filtration) or, much better, in a dynamic system, in columns with cation exchange resins. The removal of alkaline cations is very efficient, sometimes less than 1 ppm of potassium ions being obtained ... 

A 30-min 99/1->93/7 chloroform/ethanol gradient was used with a silica column (A = 254nm) to characterize styrene/methyl and ethyl methacrylate copolymers [755]. That the ethanol content was critical was shown through a series of chromatograms for a 50/50 styrene/methyl methacrylate co-polymer and a 35/65 styrene/ethyl methacrylate co-polymer. For 25 pL injections of 0.1% w/v samples, the 50/50 co-polymer completely eluted with a 97/3 chloroform/ethanol mobile phase but was completely adsorbed to the silica at 99/1. Similarly, the 35/65 copolymer eluted at 95/5 chloroform/ethanol and did not elute at 98/2. Temperature effects (40-70°C) on the level of ethanol needed for elution were tabulated for these co-polymers as well. 

Jackson and Walker [7] studied the applicability of pyrolysis combined with capillary column GC to the examination of phenyl polymers (e.g., styrene-isoprene copolymer) and phenyl ethers e.g., bis[w-(w-phenoxy phenoxy)phenyl]ether. In the procedure the polymer sample is dissolved in benzene. The pyrolysis Curie point temperature wire is dipped 6 mm into the polymer solution. The polymer-coated wires are then placed in a vacuum oven at 75-80 °C for 30 minutes to remove the solvent. Figure 6.2 shows a characteristic pyrogram of the copolymer (isoprene-styrene) resulting from a 10-second pyrolysis at 601 °C. When the polyisoprene is pyrolysed, C2, C3, C4, isoprene, and CjoHig dimers are produced. When PS is pyrolysed, styrene and aromatic hydrocarbons are the products. Figure 6.2 shows that the copolymer product distribution and relative area basis resemble the two individual polymer product distributions. 

Jackson and Walker studied the applicability of pyrolysis combined with capillary column gas chromatography mass spectrometry to the examination of phenyl polymers (eg. styrene-isoprene copolymer) and polymer like phenyl ethers (eg. bis(m-(m-phenoxy phenoxy)phenyl)ether). They examined the effect of varying parameters affecting the nature of products formed and relative product distribution in routine pyrolysis. These parameters include the effects of pyrolysis temperature rise times, pyrolysis temperatures up to 985 C and pyrolysis duration. Temperature rise time (0.1 to 1.5 s) is not a critical factor in the Curie point pyrolysis of a styrene-isoprene copolymer, either with regard to the nature of the products formed or their relative distributions. Additionally, the variation of pyrolysis duration or hold time (2.0 to 12.5 s) at a fixed Curie temperature reflected no change in the nature of components formed however changes in product distributions were observed. Variations in Curie temperature at a fixed pyrolysis duration produced drastic changes in product distributions such as a three-... 

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