Polymer Synthesis Laboratory Equipment

THF Mobile Phase Gel Permeation Chromatograph
(GPC)

For the determination of polymer hydrodynamic volume in organic solvents, a GPC system consisting of a Waters 717 auto-injector, a Waters 515 pump working at 1 ml/min., a Waters 486 tunable absorbance detector, and a Waters 410 differential refractometer equipped with a Precision Detectors light scattering detector is used. The columns are three 60 cm Phenomenex Phenogel linear mixed bed columns with a 7.8 mm ID. The molecular weight limits are 100 to 10 million Daltons. The columns are kept at constant temperature with an Eppendorf CH-460 column heater. A solvent recycler is also in place to conserve the mobile phase.

Aqueous Mobile Phase Gel Permeation Chromatograph (GPC)

For the determination of polymer hydrodynamic volume in aqueous solvents, a GPC system consisting of a Waters manual Rheodyne injector, a Waters 510 pump working at 0.8 ml/min., and a Waters 410 differential refractometer. The columns are two Phenomenex Polysep 60 cm linear mixed bed columns with a 7.8 ID. The molecular weight cut off of these columns is 10 million Daltons. This GPC is currently running a mixture of isopropanol and water. The system also includes an Anspect degasser connected in-line to continually degas the mobile phase.

Membrane Osmometer

The instrument used for membrane osmometry is a Gonotect instrument consisting of an Osmonat 090 cell unit connected with a UIC Semi-Automatic Osmometer Control Central Unit. Membrane osmometry is based on the difference in osmotic pressure of a pure solvent and one containing a solute. A pure solvent is separated from one containing solute by a semipermeable membrane. The membrane allows solvent to flow across, but not the solute. As the pure solvent side is closed to the atmosphere, the pressure on the pure solvent side drops, and this drop is measured by a valve with a transducer attached to a thin metal diaphragm. The pressure required to equilibrate the two sides (the chemical potential difference of each side due to the presence of solute) is the osmotic pressure. Experimentally, several concentrations of solute are measured and the number average molecular weight is determined by the intercept of a plot of osmotic pressure divided by concentration vs. osmotic pressure. The molecular weight range of this technique is limited by the membranes used at the low end and the instrument's ability to measure tiny pressure changes at the high end, but is typically in the range of 10,000 to 500,000 Daltons. Membrane osmometry is an absolute method that does not require standards. It also can give information about polymer-solvent interactions derived from the second viral coefficient.

Vapor Pressure Osmometer

A UIC 070 vapor pressure Osmometer, connected with a UIC Semi-Automatic Osmometer control unit, allows the determination of molecular weights in both organic and aqueous solvents. By measuring the vapor pressure depression of sample with dissolved material as compared to the pure solvent, the number of osmotic effective particles can be determined. Combining this data with the known concentration of the sample in the solvent, the number average molecular weight (M_n) can be determined for polydisperse polymer samples. The molecular weight range in organic solvents is roughly 40 to 35,000 Daltons, and up to 10,000 Daltons in water. For biological samples, this method allows the determination of the osmolal concentration, the dissociation constants or activity coefficient.

Low Angle Laser Light Scattering Photometer

A Thermal Separation Products KMX-6 LALLS instrument is used for the determination of weight average molecular weight (M_w). This instrument measures the intensity of scattered light at a fixed angle, using a HeNe laser (632.8 nm). The scattered intensity is then compared to the intensity of the incident light. The values of this ratio at several different concentrations along with the differential refractive index of the polymer being analyzed and instrument constants are used find M_w. In practice, the light scattering intensity is measured as a function of concentration. M_w is the reciprocal of the intercept and the slope of the line is the second viral coefficient (a measure of polymer-solvent interaction). The low angle of the measurements allows the user to plot a single line and find the intercept directly. This is in contrast to techniques requiring the construction of a 2-D plot where measurements at several angles are required (Zimm plots).

Differential Refractometer

A Thermal Separation Products KMX-16 Laser Differential Refractometer is used to determine the dn/dc value of polymer solutions at 632.8 nm. The relationship of refractive index to concentration is a necessary parameter for determining weight average molecular weight from light scattering. With this instrument the value is found by using several concentrations of material, usually four, and averaging the dn/dc value of the samples. As refractive index is temperature sensitive, the sample cell is temperature controlled.

UV-Vis Spectrometer

An Agilent 8453 uv-vis spectrometer using a diode array detector. This instrument has a wavelength range of 190 nm to 1100 nm by using two different light sources. For the short wave lengths, a deuterium arc lamp is used. For the longer wave lengths, a tungsten halogen lamp is used. Due to the use of a photodiode array detector, the sample chamber does not require a cover and is left open. The instrument has a better than 2 nm resolution.

Schott Automated Viscometer

This instrument allows automated measurement of flow time for the determination of fluid viscosities. A Schott CT1450 temperature controller provides a constant temperature. The measurements are done in a thermostated bath with an Ubbelohde viscometer placed in a stand equipped with sensors to detect the passing of the liquid-air interface. A Schott AVS 360 controller monitors and controls the measurements. The system is also equipped with a ViscoDoser AVS20 capable of precisely diluting the samples being measured, allowing a series of concentrations to run automatically. There are five Ubbelohde viscometers with varying capillary sizes for measurement of a variety of viscosities.

Gas Chromatograph (GC)

A Varian Star 3400Cx GC allows for the detection of molecules in the gas phase. The instrument uses a capillary column and is equipped with a Flame Ionization Detector (FID) and thermal conductivity detector (TCD). Helium is used as the mobile phase. Samples are normally dilute solutions of volatile compounds in low boiling solvents such as diethyl ether or methanol. Peak areas of the chromatographs can then be related to the concentration of the solutes contained in the sample.