Determination of the Molar Mass Distribution of Phenol Formaldehyde Resins Using GPC

Phenol formaldehyde resins (PFR) are used in various industrial products because of their versatile properties. Thermoplastic and thermo-reactive resin types differ in the degree of remaining reactive groups and their molar mass distribution (MMD). We compared the MMDs of two phenolic resins by gel permeation chromatography (GPC).

Phenol formaldehyde resins are condensation polymers. They are obtained by condensing phenol with formaldehyde in the presence of an acidic or alkaline catalyst. Depending on the synthesis conditions (comonomer ratio, pH), thermoplastic novolac and thermo-reactive resol types can be formed. The development of molar mass distributions in a thermo-reactive (PFR 1) and a thermoplastic (PFR 2) resin can be analyzed by GPC.

Experimental Conditions

Analysis was performed on an EcoSEC GPC System with refractive index (RI) detector using a bank of two semi-micro GPC columns (6.0 mm × 150 mm, 3 μm) with different exclusion limits. MMDs were determined for each sample using a calibration curve that was created at the same experimental conditions with Tosoh polystyrene standards. Calibration curve data were fitted with a cubic function and error values were less than 5%.

Columns: 1 × TSKgel SuperH2500 + 1 × TSKgel SuperH2000 (6.0 × 150 mm, 3 μm)
Mobile phase: THF
Flow rate:        0.35 mL/min
Temperature:  40 °C
Sample:           PFR 1, PFR 2 (5.0 mg/mL THF)
Injection volume:        30 μL
Detection:       Refractive index

Results

Figure 1 shows GPC elution curves for the two PFR samples. Molecules of PFR 1 start eluting later than those of PFR 2. The use of two semi-micro TSKgel columns in series with different exclusion limits delivered the best resolution for different molar mass distributions within each sample even at the very low molar mass range.

The GPC chromatograms show multiple MMDs for both resins. Based on the polystyrene calibration curve, MMDs were calculated (Figure 2). PFR 1 shows a lower molar mass distribution than PFR 2.

Conclusion

The MMDs of two PFR resins were determined via a dual flow RI detector using the EcoSEC GPC system and semi-micro GPC columns. The GPC analysis shows that the resol type PFR 1 resins have low MMDs compared to the thermoplastic PFR 2 resin. Highly resolved multiple MMDs were observed for both resins. This study shows that GPC is a powerful tool to study the molar mass variations of PFR resins. In addition, the semi-micro design of the EcoSEC GPC system allows the use of semi-micro columns, resulting in reduced solvent consumption and analysis time compared to conventional GPC analysis.

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