Preparative GPC instrument

GPC may be used to prepare shaip fractions of cyclic and linear PDMS with number average numbers of skeletal bonds in the range 100 < n < 1000. The preparative GPC instrument used for this purpose is described below. The cyclic and linear PDMS fractions obtained this way typically have dispersities (M / MJ of 1.05 0.05, considerably lower than those obtained using conventional fractionation techniques. 

Preparative GPC Instrument. Preparative scale GPC units typically involve the use of much larger separation columns, greater solvent volumes and relatively larger amounts of sample than conventional analytical systems. The Preparative GPC instrument used to prepare sharp fractions of polymers was designed and constructed by Mr. D. Sympson at the workshops of the University of York Chemistry Department [5]. A block diagram of the instrument is shown in Figure 5. 

The polydisperse per-deuterated cyclic PDMS recovered from the catalytic reaction was fractionated in to twelve sharp fractions using the preparative GPC instrument detailed earlier [5]. A section of the preparative trace is shown in Figure 35. The fractions were an ysed using analytical GPC calibrated with cyclic PDMS standards and the results of the analysis are shown in Table IV. 

The conformational and dynamic properties of cyclic polymers have been the subject of considerable interest over a number of years [73] [74]. The new synthetic procedure developed for the preparation of per-deuterated cyclic and linear poly(dimethylsiloxane) (PDMS) polymers [12] [13] [14] now offers unique possibilities for neutron scattering studies. For the first time, it has allowed sufficient deuterated materials to be available for fractionation using our preparative GPC instrument. The resulting narrow fractions are ideally suited for both static and dynamic studies of cyclic and linear polymers. This range incorporates the critical molar mass for entanglement in PDMS. 

Fortunately, as the complexity of macromolecules increases, the precision and sophistication of instruments designed for their characterization improve. The analytical and preparative fractionating columns of GPC used in the 1950s are transformed into automatic multicolumn, multi-detector, high-temperature SEC. Similar advance is observed for TREF and CRYSTAF, now fused into CFC. At the same time, new methods are being developed for faster and more precise characterization by means of the multi-detector liquid chromatography, HTLC or HPLC. 

GPC is now widely used both for analysis of molar-mass distributions and the preparation of sharp fractions of many polymers. There can be problems with instrumental broadening whereby sharp fractions will yield a broad curve on the chromatogram. However, with care, accurate and reliable results can be obtained for certain polymers in a short period of time (2-4 hours) using only a few milligrams of sample. 

A 3.160 mg/mL solution of PMMA in chloroform was prepared. One sample of 100 oL was injected into a Waters 150CALC GPC with an internal viscometer, Viscotek Model T60A, and an external refractive index instrument. The flow rate of the run was 1.000 mL/min. 

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